/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*-------------------------------------------------------------------------
 *
 * cdbquerydispatchingcontext.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <sys/fcntl.h>

#include "access/genam.h"
#include "access/heapam.h"
#include "access/pxfuriparser.h"
#include "access/parquetsegfiles.h"
#include "access/tuptoaster.h"
#include "catalog/aoseg.h"
#include "catalog/catalog.h"
#include "catalog/catquery.h"
#include "catalog/pg_amop.h"
#include "catalog/pg_amproc.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_language.h"
#include "catalog/pg_type.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_attrdef.h"
#include "catalog/pg_attribute_encoding.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_exttable.h"
#include "catalog/pg_magic_oid.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_tablespace.h"
#include "catalog/toasting.h"
#include "cdb/cdbdispatchedtablespaceinfo.h"
#include "cdb/cdbfilesystemcredential.h"
#include "cdb/cdbpartition.h"
#include "cdb/cdbquerycontextdispatching.h"
#include "cdb/cdbvars.h"
#include "commands/dbcommands.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "optimizer/prep.h"
#include "storage/fd.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/uri.h"

/**
 * all opened file on shared storage will be removed after transaction terminated.
 */
struct DropListItemData
{
    char *path;
    struct DropListItemData *next;
};
typedef struct DropListItemData DropListItemData;

typedef struct DropListItemData *DropListItem;

static DropListItem DropList = NULL;

int QueryContextDispatchingSizeMemoryLimit = 100 * 1024; /* KB */

/*
 * |------type id : 1 byte---------|
 * |---content length : 4 byte-----|
 * |---variable length content-----|
 */

/*
 * |------type id : 1 byte---------|
 * |-----fixed length content -----|
 */

enum QueryContextDispatchingItemType
{
    MasterXid, TablespaceLocation, TupleType, EmptyTable, FileSystemCredential, Namespace
};
typedef enum QueryContextDispatchingItemType QueryContextDispatchingItemType;

enum QueryContextDispatchingObjType
{
	RelationType,
	TablespaceType,
	NamespaceType,
	ProcType,
	AggType,
	LangType,
	TypeType,
	OpType,
	OpClassType
};
typedef enum QueryContextDispatchingObjType QueryContextDispatchingObjType;

struct QueryContextDispatchingHashKey
{
    Oid objid;
    QueryContextDispatchingObjType type;
};
typedef struct QueryContextDispatchingHashKey QueryContextDispatchingHashKey;

struct QueryContextDispatchingHashEntry
{
    QueryContextDispatchingHashKey key;
    Oid aoseg_relid;  /* pg_aoseg_* or pg_aocsseg_* relid */
   /* aoseg_index_relid in future */
};
typedef struct QueryContextDispatchingHashEntry QueryContextDispatchingHashEntry;

static void
prepareDispatchedCatalogAuthUser(QueryContextInfo *ctx, Oid userOid);

static void
prepareDispatchedCatalogFunction(QueryContextInfo *ctx, Oid procOid);

static void
prepareDispatchedCatalogLanguage(QueryContextInfo *ctx, Oid langOid);

static void
prepareDispatchedCatalogOpClassForType(QueryContextInfo *ctx, Oid typeOid);

static void
prepareDispatchedCatalogType(QueryContextInfo *ctx, Oid typeOid);

static void
prepareDispatchedCatalogOperator(QueryContextInfo *ctx, Oid opOid);

static void
prepareDispatchedCatalogOpClass(QueryContextInfo *ctx, Oid opclass);

static void
prepareDispatchedCatalogAggregate(QueryContextInfo *ctx, Oid aggfuncoid);

static void
prepareDispatchedCatalogFunctionExpr(QueryContextInfo *cxt, Expr *expr);

static void
prepareDispatchedCatalogForAoParquet(QueryContextInfo *cxt, Oid relid,
								        bool forInsert, List *segnos);
static void
prepareAllDispatchedCatalogTablespace(QueryContextInfo *ctx);

static void
prepareDispatchedCatalogExternalTable(QueryContextInfo *cxt, Oid relid);

static void
prepareDfsAddressForDispatch(QueryContextInfo* cxt);

static void
addOperatorToDispatchContext(QueryContextInfo *ctx, Oid opOid);

static void
WriteData(QueryContextInfo *cxt, const char *buffer, int size);

static void GetExtTableLocationsArray(HeapTuple tuple, TupleDesc exttab_desc, 
									  Datum **array, int *array_size);
static char* 
GetExtTableFirstLocation(Datum *array);

static void 
AddFileSystemCredentialForPxfTable();

/**
 * construct the file location for query context dispatching.
 */
static void
GetQueryContextDipsatchingFileLocation(char **buffer)
{
    int len;

    static int count = 0;

    char *path = NULL, *pos;
    Oid tablespace = get_database_dts(MyDatabaseId);

    GetFilespacePathForTablespace(tablespace, &path);

    if (NULL == path)
    {
        elog(ERROR, "cannot get distributed table space location for current database,"
                " table space oid is %u",
                tablespace);
    }

    pos = path + strlen(path) - 1;

    *pos = '\0';

    len = strlen(path);
    len += 64;

    *buffer = palloc(len);

    snprintf(*buffer, len, "%s-1/session_%d_id_%d_query_context", path, gp_session_id, ++count);

    pfree(path);

}
/*
 * create a QueryContextInfo and fill the location of file on shared storage.
 *
 * also add auxiliary information such as master's transaction into QueryContextInfo.
 */
QueryContextInfo *
CreateQueryContextInfo(void)
{
    QueryContextInfo *retval = makeNode(QueryContextInfo);

    retval->htab = createPrepareDispatchedCatalogRelationDisctinctHashTable();

    GetQueryContextDipsatchingFileLocation(&retval->sharedPath);

    AddAuxInfoToQueryContextInfo(retval);

    retval->finalized = false;

    return retval;
}

/*
 * On QE, construct a QueryContextInfo from a file on shared storage.
 */
void
InitQueryContextInfoFromFile(QueryContextInfo *cxt)
{
    Assert(NULL != cxt->sharedPath);

    cxt->file = PathNameOpenFile(cxt->sharedPath, O_RDONLY, 0);

    if (cxt->file < 0)
	{
    	ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("cannot open file %s %m", cxt->sharedPath),
					 errdetail("%s", HdfsGetLastError())));
	}

}

/*
 * close  a QueryContextInfo and close its file if it is opened.
 */
void
FinalizeQueryContextInfo(QueryContextInfo *cxt)
{
    Assert(cxt);
    Assert(!cxt->finalized);

    if (Debug_querycontext_print && Gp_role != GP_ROLE_EXECUTE)
    {
        int size = cxt->cursor;
        if (cxt->useFile)
        {
            size = FileNonVirtualTell(cxt->file);

            if (size < 0)
            {
            	ereport(ERROR,
						(errcode_for_file_access(),
								errmsg("failed to get file point position"),
										errdetail("%s", HdfsGetLastError())));
            }
        }

        elog(LOG, "query context size: %d bytes, passed by %s",
                size, (cxt->useFile? "shared storage" : "dispatching"));

    }

    if (cxt->htab)
    	hash_destroy(cxt->htab);

    if (enable_secure_filesystem && Gp_role != GP_ROLE_EXECUTE)
    {
    	int size;
    	char *credential;

        StringInfoData buffer;
        initStringInfo(&buffer);

        credential = serialize_filesystem_credentials(&size);

        if (credential && size > 0)
        {
			pq_sendint(&buffer, (int) FileSystemCredential, sizeof(char));
			pq_sendint(&buffer, size, sizeof(int));

			WriteData(cxt, buffer.data, buffer.len);
			WriteData(cxt, credential, size);
        }
    }

    if (cxt->useFile)
    {
        FileClose(cxt->file);
        cxt->file = 0;
    }

    cxt->finalized = true;
}

/*
 * cleanup and destory a QueryContextInfo
 */
void
DropQueryContextInfo(QueryContextInfo *cxt)
{
    Assert(NULL != cxt);

    if (TestFileValid(cxt->file))
        FileClose(cxt->file);

    if (cxt->sharedPath)
        pfree(cxt->sharedPath);

    if (cxt->buffer)
        pfree(cxt->buffer);

    if (cxt->errTblOid)
    	list_free(cxt->errTblOid);

    pfree(cxt);
}

/*
 * add a file to drop list.
 */
static void
AddToDropList(const char *path)
{
    MemoryContext old;
    old = MemoryContextSwitchTo(TopTransactionContext);

    DropListItem p = palloc(sizeof(DropListItemData));
    p->path = palloc(strlen(path) + 1);
    strcpy(p->path, path);

    p->next = DropList;
    DropList = p;

    MemoryContextSwitchTo(old);
}

/*
 * called when transaction commit/rollback to drop all pending files.
 */
void
AtEOXact_QueryContext(void)
{
    DropListItem p, q;
    for (p = DropList; NULL != p;)
    {
        Assert(p->path);
        RemovePath(p->path, FALSE);

        q = p;
        p = p->next;

        pfree(q->path);
        pfree(q);
    }

    DropList = NULL;
}

/*
 * read from file until get expected size of bytes or reach end of file.
 * return TRUE if read successfully, return FALSE when reach end of file.
 *
 * report error if reach end of file and errorOnEof is true.
 */
static bool
ReadFully(File file, const char *path, char *buffer, int size,
        bool errorOnEof)
{
    int done, todo = size;

    while (todo > 0)
    {
        done = FileRead(file, buffer + size - todo, todo);

        if (0 == done && errorOnEof)
        {
            ereport(ERROR,
					(errcode(ERRCODE_IO_ERROR),
							errmsg( "rebuild query context failed:" " can not read data since unexpected eof")));
        }
        else if (0 == done)
        {
            return FALSE;
        }
        else if (done < 0)
        {
            ereport(ERROR,
					(errcode(ERRCODE_IO_ERROR),
							errmsg( "rebuild query context failed:" " can not read data from %s", path),
							errdetail("%s", HdfsGetLastError())));
        }

        todo -= done;
    }

    return TRUE;
}

/*
 * read from QueryContextInfo until get expected size of bytes or reach end of file.
 * return TRUE if read successfully, return FALSE when reach end of file.
 *
 * report error if reach end of file and errorOnEof is true.
 */
static bool
ReadData(QueryContextInfo *cxt, char *buffer, int size,
        bool errorOnEof)
{
    Assert(NULL != cxt);
    Assert(NULL != buffer);
    Assert(size > 0);

    if (!cxt->useFile)
    {
        Assert(cxt->buffer);
        if (cxt->size == cxt->cursor && errorOnEof)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_IO_ERROR), errmsg( "rebuild query context failed: "
                    "can not read data since unexpected eof")));
        }
        else if (cxt->size == cxt->cursor)
        {
            return FALSE;
        }
        else if (cxt->size - cxt->cursor < size)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_IO_ERROR), errmsg( "rebuild query context failed: "
                    "can not read data since unexpected eof")));

        }

        memcpy(buffer, cxt->buffer + cxt->cursor, size);
        cxt->cursor += size;

        return TRUE;

    }
    else
    {
        Assert(TestFileValid(cxt->file));
        return ReadFully(cxt->file, cxt->sharedPath, buffer, size, errorOnEof);
    }
}

/*
 * write data into QueryContextInfo
 */
static void
WriteData(QueryContextInfo *cxt, const char *buffer, int size)
{

    Assert(NULL != cxt);
    Assert(NULL != buffer);
    Assert(size > 0);

    if (cxt->useFile)
    {
        Assert(TestFileValid(cxt->file));

        if (size != FileWrite(cxt->file, buffer, size))
        {
            ereport(ERROR,
					(errcode(ERRCODE_IO_ERROR),
							errmsg( "prepare query context failed: " "can not write data into file: %s", cxt->sharedPath),
							errdetail("%s", HdfsGetLastError())));
        }

        return;
    }

    /* switch to file*/
    if (false /*disable this feature*/ && cxt->cursor + size > QueryContextDispatchingSizeMemoryLimit *1024)
    {
        elog(LOG, "Switch to use file on shared storage : %s "
                "instead of dispatching the query context "
                    "since memory usage exceed the gp_query_context_mem_limit", cxt->sharedPath);

        cxt->useFile = TRUE;

        char *p;
        char *dir = palloc(strlen(cxt->sharedPath) + 1);
        strcpy(dir, cxt->sharedPath);
        p = strrchr(dir, '/');

        if (NULL == p)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_INTERNAL_ERROR), errmsg("failed to construct"
                    " query context directory, file path: %s", cxt->sharedPath)));

        }
        *p = 0;

        MakeDirectory(dir, 0700);

        cxt->file = PathNameOpenFile(cxt->sharedPath, O_CREAT | O_WRONLY, 0500);

        if (cxt->file < 0)
        {
        	ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("cannot create file %s %m", cxt->sharedPath),
					 errdetail("%s", HdfsGetLastError())));
        }

        AddToDropList(cxt->sharedPath);

        if (cxt->cursor > 0)
        {
            if (cxt->cursor != FileWrite(cxt->file, cxt->buffer, cxt->cursor))
            {
                ereport(ERROR,
						(errcode(ERRCODE_IO_ERROR),
								errmsg( "prepare query context failed: " "can not write data into file: %s", cxt->sharedPath),
								errdetail("%s", HdfsGetLastError())));
            }
        }
        if (cxt->buffer)
            pfree(cxt->buffer);
        cxt->buffer = NULL;
        cxt->size = cxt->cursor = 0;

        WriteData(cxt, buffer, size);
    }
    else
    {
        if (cxt->cursor + size > cxt->size)
        {
            cxt->size = (1 + cxt->size) * 2;

			if (cxt->size < cxt->cursor + size)
				cxt->size = cxt->cursor + size;

            if (cxt->buffer)
                cxt->buffer = repalloc(cxt->buffer, cxt->size);
            else
                cxt->buffer = palloc(cxt->size);
        }
        memcpy(cxt->buffer + cxt->cursor, buffer, size);
        cxt->cursor += size;
    }
}

/*
 * get and set master's transaction on QE
 */
static void
RebuildMasterTransactionId(QueryContextInfo *cxt)
{
    Assert(Gp_role == GP_ROLE_EXECUTE);

    TransactionId masterXid;

    char buffer[4];
    ReadData(cxt, buffer, sizeof(buffer), TRUE);

    masterXid = (TransactionId) ntohl(*(uint32 *)buffer);

    SetMasterTransactionId(masterXid);
}

static void
RebuildFilesystemCredentials(QueryContextInfo *cxt, HTAB ** currentFilesystemCredentials,
        MemoryContext *currentFilesystemCredentialsMemoryContext)
{
	Assert(Gp_role == GP_ROLE_EXECUTE);

	int len;
	char buffer[4], *binary;

	Insist(enable_secure_filesystem);

	ReadData(cxt, buffer, sizeof(buffer), TRUE);

	len = (int) ntohl(*(uint32 *)buffer);

	binary = palloc(len);
	ReadData(cxt, binary, len, TRUE);
	deserialize_filesystem_credentials(binary, len, currentFilesystemCredentials,
	        currentFilesystemCredentialsMemoryContext);

	pfree(binary);
}

/*
 * build a new empty in-memory table with given relid.
 */
static void
RebuildEmptyTable(QueryContextInfo *cxt)
{
    Oid relid;
    char buffer[4];

    Relation rel;
    InMemHeapRelation inmemrel;

    ReadData(cxt, buffer, sizeof(buffer), TRUE);

    relid = (Oid) ntohl(*(uint32 *)buffer);

    inmemrel = OidGetInMemHeapRelation(relid, INMEM_HEAP_MAPPING);
    Assert(NULL == inmemrel);

    rel = heap_open(relid, AccessShareLock);
    inmemrel = InMemHeap_Create(relid, rel, TRUE, 10, AccessShareLock,
            RelationGetRelationName(rel), FALSE, 0, INMEM_HEAP_MAPPING);
    Assert(NULL != inmemrel);

}

/*
 * get and set a tablespace location on QE.
 */
static void
RebuildTablespaceLocation(QueryContextInfo *cxt)
{
    Assert(Gp_role == GP_ROLE_EXECUTE);

    int32 len;
    Oid tspoid;
    char location[FilespaceLocationBlankPaddedWithNullTermLen];

    char *buffer, *loc;
    buffer = palloc(sizeof(int32));

    ReadData(cxt, buffer, sizeof(int32), TRUE);

    len = (TransactionId) ntohl(*(uint32 *)buffer);
    buffer = repalloc(buffer, len);

    ReadData(cxt, buffer, len, TRUE);
    tspoid = (Oid) ntohl(*(uint32 *)buffer);

    loc = buffer + sizeof(Oid);

    snprintf(location, FilespaceLocationBlankPaddedWithNullTermLen,
            buffer + sizeof(Oid), 0);

    DispatchedFilespace_AddForTablespace(tspoid, location);

    pfree(buffer);

}

static void
EnableInMemHeapWithIndexScan(Oid relid, bool *enable, int *attrno)
{
    Assert(NULL != enable && NULL != attrno);

    switch(relid)
    {
        case AttributeRelationId:
            *enable = true;
            *attrno = Anum_pg_attribute_attrelid;
            break;
        default:
            *enable = false;
            *attrno = 0;
    }
}


/*
 * get and insert a tuple into in-memory table.
 */
static void
RebuildTupleForRelation(QueryContextInfo *cxt)
{
    Assert(Gp_role == GP_ROLE_EXECUTE);

    Oid relid;
    int32 len, contentid, tuplen;

    char *buffer;
    Relation rel;
    InMemHeapRelation inmemrel;

    HeapTuple tuple;

    buffer = palloc(sizeof(int32));

    ReadData(cxt, buffer, sizeof(int32), TRUE);
    len = (int32) ntohl(*(uint32*)buffer);

    ReadData(cxt, buffer, sizeof(int32), TRUE);
    relid = (Oid) ntohl(*(uint32*)buffer);

    ReadData(cxt, buffer, sizeof(int32), TRUE);
    contentid = (int32) ntohl(*(uint32*)buffer);

    tuplen = len - sizeof(Oid) - sizeof(int32);
    Assert(tuplen > 0);

    buffer = repalloc(buffer, tuplen);
    ReadData(cxt, buffer, tuplen, TRUE);

    if (contentid == MASTER_CONTENT_ID || contentid == GpIdentity.segindex)
    {
        tuple = (HeapTuple) buffer;
        tuple->t_data = (HeapTupleHeader) ((char *) tuple
                + sizeof(HeapTupleData));

        inmemrel = OidGetInMemHeapRelation(relid, INMEM_HEAP_MAPPING);

        if (NULL == inmemrel)
        {
            bool indexOk;
            int attrno;

            rel = heap_open(relid, AccessShareLock);

            EnableInMemHeapWithIndexScan(relid, &indexOk, &attrno);

            inmemrel = InMemHeap_Create(relid, rel, TRUE, 10, AccessShareLock,
                    RelationGetRelationName(rel), indexOk, attrno, INMEM_HEAP_MAPPING);
            Assert(NULL != inmemrel);
        }

        InMemHeap_Insert(inmemrel, tuple, contentid);

        if (Debug_querycontext_print)
        {
            elog( LOG, "Query Context: rebuild tuple for relation %s, relid %u:",
                    inmemrel->relname, inmemrel->relid);
        }

        if (Debug_querycontext_print_tuple)
        {
            elog( LOG, "rebuild query context tuple for relation:"
                    " %s, total bytes: %d",inmemrel->relname,
                    (int)(len + sizeof(char) + sizeof(int32)));
        }

        pfree(buffer);
    }
}

/*
 * Deserialize the Namespace data
 */
static void
RebuildNamespace(QueryContextInfo *cxt)
{

	MemoryContext oldContext;
	int len;
	char buffer[4], *binary;
	oldContext = MemoryContextSwitchTo(MessageContext);
	ReadData(cxt, buffer, sizeof(buffer), TRUE);

	len = (int) ntohl(*(uint32 *) buffer);
	binary = palloc(len);
	if(ReadData(cxt, binary, len, TRUE))
	{
		dfs_address = pstrdup(binary);
	} else {
		pfree(binary);
		MemoryContextSwitchTo(oldContext);
		elog(ERROR, "Couldn't rebuild Namespace");
	}
	pfree(binary);
	MemoryContextSwitchTo(oldContext);
}

/*
 * rebuild execute context
 */
void
RebuildQueryContext(QueryContextInfo *cxt, HTAB **currentFilesystemCredentials,
        MemoryContext *currentFilesystemCredentialsMemoryContext)
{
    char type;

    while (TRUE)
    {
        if (!ReadData(cxt, &type, sizeof(char), FALSE))
            break;

        switch (type)
        {
        case MasterXid:
            RebuildMasterTransactionId(cxt);
            break;
        case TablespaceLocation:
            RebuildTablespaceLocation(cxt);
            break;
        case TupleType:
            RebuildTupleForRelation(cxt);
            break;
        case EmptyTable:
            RebuildEmptyTable(cxt);
            break;
        case FileSystemCredential:
        	RebuildFilesystemCredentials(cxt, currentFilesystemCredentials,
        	        currentFilesystemCredentialsMemoryContext);
        	break;
        case Namespace:
            RebuildNamespace(cxt);
            break;
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_GP_INTERNAL_ERROR), errmsg( "unrecognized "
                    "QueryContextDispatchingItemType %d", (int) type)));
        }
    }

    cxt->finalized = false;
	/*
	 * This is a bit overkill, but since we don't yet have a decent way to
	 * determine individual cache entries affected by the dispatched
	 * metadata, we should release all the system cache here.  Our good-old
	 * shared invalidation message is not necessarily applicable here;
	 * backends in segments never change the metadata and we care the
	 * metadata changes only within the session.
	 */
	ResetSystemCaches();
}

/*
 * collect QD's transaction id and other global variables
 */
void
AddAuxInfoToQueryContextInfo(QueryContextInfo *cxt)
{
    Assert(NULL != cxt);
    Assert(!cxt->finalized);

    StringInfoData buffer;
    initStringInfo(&buffer);

    /*
     * add master's transaction id. It will be used in external table
     */
    pq_sendint(&buffer, (int) MasterXid, sizeof(char));
    pq_sendint(&buffer, GetMasterTransactionId(), sizeof(TransactionId));

    /*
     * may add other here
     */
    WriteData(cxt, buffer.data, buffer.len);

    pfree(buffer.data);
}

/*
 * in some special case such as pg_aoseg_xxx,
 * it is a heap relation but act as a catalog.
 * and it can be empty.
 *
 * if it is empty, send this flag to QE to build a empty in-memory table.
 */
void
AddEmptyTableFlagToContextInfo(QueryContextInfo *cxt, Oid relid)
{
    StringInfoData buffer;
    initStringInfo(&buffer);

    pq_sendint(&buffer, EmptyTable, sizeof(char));
    pq_sendint(&buffer, relid, sizeof(Oid));

    WriteData(cxt, buffer.data, buffer.len);

    pfree(buffer.data);
}

/*
 * collect tuples for one catalog table
 */
void
AddTupleToContextInfo(QueryContextInfo *cxt, Oid relid,
        const char *relname, HeapTuple tuple, int32 contentid)
{
    Assert(NULL != cxt);
    Assert(!cxt->finalized);

    StringInfoData header;
    initStringInfo(&header);

    int32 tuplen = sizeof(HeapTupleData) + tuple->t_len;

    /* send one byte flag */
    pq_sendint(&header, TupleType, sizeof(char));

    /* send content length, sizeof(relid) + sizeof(contentid) + tuple */
    int32 len = sizeof(Oid) + sizeof(int32) + tuplen;
    pq_sendint(&header, len, sizeof(int32));

    /* send relid */
    pq_sendint(&header, relid, sizeof(Oid));
    pq_sendint(&header, contentid, sizeof(int32));

    WriteData(cxt, header.data, header.len);
    WriteData(cxt, (const char *) tuple, sizeof(HeapTupleData));
    WriteData(cxt, (const char *) tuple->t_data, tuple->t_len);

    pfree(header.data);

    if (Debug_querycontext_print_tuple)
    {
        elog(LOG, "query context dispatching tuple for relation: %s, "
        "total bytes: %d", relname, (int)(len + sizeof(char) + sizeof(int32)));
    }
}

/*
 * collect tuple and related toasted tuples for one catalog table
 */
void
AddTupleWithToastsToContextInfo(QueryContextInfo *cxt, Oid relid,
        const char *relname, HeapTuple tuple, int32 contentid)
{
    Relation rel, toastrel, toastidx;
    ScanKeyData toastkey;
    IndexScanDesc toastscan;
    HeapTuple ttup;
    TupleDesc	tupdesc, toasttupDesc;
    Form_pg_attribute *att;
    Datum *d;
    bool * null;
    int32  nextidx, numchunks;
    char toast_relname[NAMEDATALEN];

    Assert(NULL != cxt);
    // first add this tuple
    AddTupleToContextInfo(cxt, relid, relname, tuple, contentid);
    // add related toast tuples
    rel = heap_open(relid, AccessShareLock);
    Assert(NULL != rel);

    tupdesc = rel->rd_att;
    att = tupdesc->attrs;
    d = (Datum *)palloc(sizeof(Datum)*tupdesc->natts);
    null = (bool *)palloc(sizeof(bool)*tupdesc->natts);
    heap_deform_tuple(tuple, tupdesc, d, null);
    snprintf(toast_relname, sizeof(toast_relname), "pg_toast_%u", relid);

    for (uint i = 0; i < tupdesc->natts; i++)
    {
        if (att[i]->attisdropped)
            continue;
        if (att[i]->attlen == -1)
        {
            if(!null[i]){
                struct varlena *v=(struct varlena *) DatumGetPointer(d[i]);
                if(VARATT_IS_EXTENDED(v) && VARATT_IS_EXTERNAL(v)){
                    struct varatt_external *va_ext = copy_varatt_external(v);

                    numchunks = ((va_ext->va_extsize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
                    /*
                     * Open the toast relation and its index
                     */
                    toastrel = heap_open(va_ext->va_toastrelid, AccessShareLock);
                    toasttupDesc = toastrel->rd_att;
                    toastidx = index_open(toastrel->rd_rel->reltoastidxid, AccessShareLock);

                    /*
                     * Setup a scan key to fetch from the index by va_valueid
                     */
                    ScanKeyInit(&toastkey,
                            (AttrNumber) 1,
                            BTEqualStrategyNumber, F_OIDEQ,
                            ObjectIdGetDatum(va_ext->va_valueid));

                    /*
                     * Read the chunks by index
                     *
                     * Note that because the index is actually on (valueid, chunkidx) we will
                     * see the chunks in chunkidx order, even though we didn't explicitly ask
                     * for it.
                     */
                    nextidx = 0;
                    toastscan = index_beginscan(toastrel, toastidx,
                            SnapshotToast, 1, &toastkey);
                    while ((ttup = index_getnext(toastscan, ForwardScanDirection)) != NULL)
                    {
                        AddTupleToContextInfo(cxt, va_ext->va_toastrelid, toast_relname, ttup, contentid);
                        nextidx ++;
                    }                    
                    /*
                     * Final checks that we successfully fetched the datum
                     */
                    if (nextidx != numchunks)
                        elog(ERROR, "missing chunk number %d for toast value %u",
                                nextidx, va_ext->va_valueid);

                    /*
                     * End scan and close relations
                     */
                    index_endscan(toastscan);
                    index_close(toastidx, AccessShareLock);
                    heap_close(toastrel, AccessShareLock);
                    pfree(va_ext);
                }
            }
        }
    }
    pfree(d);
    pfree(null);

    heap_close(rel, AccessShareLock);
}
/*
 * collect tablespace location.
 */
void
AddTablespaceLocationToContextInfo(QueryContextInfo *cxt, Oid tspoid,
        const char *fmt)
{
    Assert(NULL != cxt);
    Assert(!cxt->finalized);

    StringInfoData header;
    initStringInfo(&header);

    int len = strlen(fmt);

    pq_sendint(&header, TablespaceLocation, sizeof(char));
    pq_sendint(&header, sizeof(Oid) + len + 1, sizeof(int32));
    pq_sendint(&header, tspoid, sizeof(Oid));

    WriteData(cxt, header.data, header.len);
    WriteData(cxt, fmt, len + 1);

    pfree(header.data);
}

static bool
alreadyAddedForDispatching(HTAB *rels, Oid objid, QueryContextDispatchingObjType type) {
    bool found = false;

    Assert(NULL != rels);

    QueryContextDispatchingHashKey item;

    item.objid = objid;
    item.type = type;

    hash_search(rels, &item, HASH_ENTER, &found);

    return found;
}


/*
 * collect pg_namespace tuples for oid.
 * add them to in-memory heap table for dispatcher
 */
void
prepareDispatchedCatalogNamespace(QueryContextInfo *cxt, Oid namespace)
{
    HeapTuple tuple;

    if (namespace == PG_CATALOG_NAMESPACE || namespace == PG_TOAST_NAMESPACE
            || namespace == PG_BITMAPINDEX_NAMESPACE
            || namespace == PG_PUBLIC_NAMESPACE
            || namespace == PG_AOSEGMENT_NAMESPACE)
        return;

    if (alreadyAddedForDispatching(cxt->htab, namespace, NamespaceType))
        return;

    tuple = SearchSysCache(NAMESPACEOID, ObjectIdGetDatum(namespace), 0, 0, 0);

    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for namespace %u", namespace);

    AddTupleWithToastsToContextInfo(cxt, NamespaceRelationId, "pg_namespace", tuple,
            MASTER_CONTENT_ID);

    ReleaseSysCache(tuple);
}

static void
prepareDispatchedCatalogFileSystemCredential(const char *path)
{
	if (!enable_secure_filesystem)
		return;

	Insist(Gp_role != GP_ROLE_EXECUTE);

	add_filesystem_credential(path);
}

/*
 * collect pg_tablespace tuples for oid.
 * add them to in-memory heap table for dispatcher
 */
void
prepareDispatchedCatalogTablespace(QueryContextInfo *cxt, Oid tablespace)
{

    char *path = NULL, *pos;
    char location[FilespaceLocationBlankPaddedWithNullTermLen];

    if (IsBuiltinTablespace(tablespace) || tablespace == InvalidOid )
        return;

    if (alreadyAddedForDispatching(cxt->htab, tablespace, TablespaceType))
        return;

    GetFilespacePathForTablespace(tablespace, &path);

    Assert(NULL != path);
    Assert(strlen(path) < FilespaceLocationBlankPaddedWithNullTermLen);

    prepareDispatchedCatalogFileSystemCredential(path);

    pos = path + strlen(path) - 1;
//    Assert('0' == *pos);

    *(pos+1) = '\0';
    snprintf(location, FilespaceLocationBlankPaddedWithNullTermLen,
            "%s", path);

    pfree(path);

    AddTablespaceLocationToContextInfo(cxt, tablespace, location);
}

/*
 * collect all pg_tablespace tuples for oid.
 * add them to in-memory heap table for dispatcher.
 */
static void
prepareAllDispatchedCatalogTablespace(QueryContextInfo *ctx)
{
	Relation rel;
	HeapScanDesc scandesc;
	HeapTuple tuple;

	/* Scan through all tablespaces */
	rel = heap_open(TableSpaceRelationId, AccessShareLock);
	scandesc = heap_beginscan(rel, SnapshotNow, 0, NULL);
	tuple = heap_getnext(scandesc, ForwardScanDirection);
	while (HeapTupleIsValid(tuple))
	{
		Oid tsOid;

		tsOid = HeapTupleGetOid(tuple);
		/*Don't include shared relations */
		if (!IsBuiltinTablespace(tsOid))
		{
			prepareDispatchedCatalogTablespace(ctx, tsOid);
		}
		tuple = heap_getnext(scandesc, ForwardScanDirection);
	}
	heap_endscan(scandesc);
	heap_close(rel, AccessShareLock);

	return;
}

/*
 * to check if a type is a composite type,
 * dispatching type info if it is.
 */
static void
prepareDispatchedCatalogCompositeType(QueryContextInfo *cxt,
        Oid typeid)
{
    HeapTuple tuple;

    Form_pg_type attr;

    Assert(OidIsValid(typeid));

    tuple = SearchSysCache(TYPEOID, ObjectIdGetDatum(typeid), 0, 0, 0);

    if (!HeapTupleIsValid(tuple))
        return;

    attr = (Form_pg_type) GETSTRUCT(tuple);

    if (attr->typtype == TYPTYPE_COMPOSITE)
        prepareDispatchedCatalogSingleRelation(cxt, attr->typrelid, FALSE, 0);

    ReleaseSysCache(tuple);
}

/*
 * collect relation's attribute info for dispatching
 */
static void
prepareDispatchedCatalogAttribute(QueryContextInfo *cxt,
        Oid reloid)
{
    Relation rel;
    HeapTuple attrtuple;

    ScanKeyData skey;
    SysScanDesc scandesc;

    Form_pg_attribute attr;

    rel = heap_open(AttributeRelationId, AccessShareLock);
    Assert(NULL != rel);

    ScanKeyInit(&skey, Anum_pg_attribute_attrelid, BTEqualStrategyNumber,
            F_OIDEQ, ObjectIdGetDatum(reloid));
    scandesc = systable_beginscan(rel, AttributeAttrelidIndexId, TRUE, SnapshotNow, 1,
            &skey);
    attrtuple = systable_getnext(scandesc);
    while (HeapTupleIsValid(attrtuple))
    {
        attr = (Form_pg_attribute) GETSTRUCT(attrtuple);

        if (attr->attnum > 0)
        {
            /* check attribute type */
            if (OidIsValid(attr->atttypid))
                prepareDispatchedCatalogCompositeType(cxt, attr->atttypid);
        }

        AddTupleToContextInfo(cxt, AttributeRelationId, "pg_attribute",
                attrtuple, MASTER_CONTENT_ID);

        attrtuple = systable_getnext(scandesc);
    }
    systable_endscan(scandesc);

    heap_close(rel, AccessShareLock);
}

/*
 * collect relation's defalut values for dispatching
 */
static void
prepareDispatchedCatalogAttributeDefault(QueryContextInfo *cxt,
        Oid reloid)
{
    Relation rel;
    Datum value;
    HeapTuple attrdeftuple;

    ScanKeyData skey;
    SysScanDesc scandesc;

    rel = heap_open(AttrDefaultRelationId, AccessShareLock);

    ScanKeyInit(&skey, Anum_pg_attrdef_adrelid, BTEqualStrategyNumber, F_OIDEQ,
            ObjectIdGetDatum(reloid));
    scandesc = systable_beginscan(rel, InvalidOid, FALSE, SnapshotNow, 1,
            &skey);
    attrdeftuple = systable_getnext(scandesc);
    while (HeapTupleIsValid(attrdeftuple))
    {
        /*
         * check for sequence
         */
        Expr *expr = NULL;
        bool isNull;

        value = fastgetattr(attrdeftuple, Anum_pg_attrdef_adbin,
                RelationGetDescr(rel), &isNull);

        Assert(FALSE == isNull);

        expr = stringToNode(TextDatumGetCString(value));
        if (expr)
        {
            prepareDispatchedCatalogFunctionExpr(cxt, expr);
            pfree(expr);
        }

        AddTupleWithToastsToContextInfo(cxt, AttrDefaultRelationId, "pg_attrdef",
                attrdeftuple, MASTER_CONTENT_ID);
        attrdeftuple = systable_getnext(scandesc);
    }
    systable_endscan(scandesc);

    heap_close(rel, AccessShareLock);

}

/*
 * collect relation's attribute encoding for dispatching
 */
static void
prepareDispatchedCatalogAttributeEncoding(QueryContextInfo *cxt,
		Oid reloid)
{
    Relation rel;
    HeapTuple tuple;

    ScanKeyData skey;
    SysScanDesc scandesc;

    Form_pg_attribute_encoding attr;

    rel = heap_open(AttributeEncodingRelationId, AccessShareLock);
    Assert(NULL != rel);

    ScanKeyInit(&skey, Anum_pg_attribute_encoding_attrelid, BTEqualStrategyNumber,
            F_OIDEQ, ObjectIdGetDatum(reloid));
    scandesc = systable_beginscan(rel, AttributeEncodingAttrelidIndexId, TRUE, SnapshotNow, 1,
            &skey);
    tuple = systable_getnext(scandesc);
    while (HeapTupleIsValid(tuple))
    {
        attr = (Form_pg_attribute_encoding) GETSTRUCT(tuple);

        AddTupleWithToastsToContextInfo(cxt, AttributeEncodingRelationId, "pg_attribute_encoding",
                tuple, MASTER_CONTENT_ID);

        tuple = systable_getnext(scandesc);
    }
    systable_endscan(scandesc);

    heap_close(rel, AccessShareLock);

}

/*
 * collect relation's type info for dispatching
 */
static void
prepareDispatchedCatalogTypeByRelation(QueryContextInfo *cxt,
        Oid relid, HeapTuple classtuple)
{
    Datum typeid;
    HeapTuple typetuple;

    typeid = SysCacheGetAttr(RELOID, classtuple, Anum_pg_class_reltype, NULL );

    if (InvalidOid == DatumGetObjectId(typeid))
        elog(ERROR, "reltype in pg_class for %u is invalid", relid);

    typetuple = SearchSysCache(TYPEOID, typeid, 0, 0, 0);

    AddTupleWithToastsToContextInfo(cxt, TypeRelationId, "pg_type", typetuple,
            MASTER_CONTENT_ID);

    /*
     * TODO:
     * 1) to check typelem for array type
     * 2) to check referenced tuple in pg_proc
     * 3) to check text type attributes
     */
    ReleaseSysCache(typetuple);
}

/*
 * collect pg_constraint for metadata dispatching
 */
static void
prepareDispatchedCatalogConstraint(QueryContextInfo *cxt,
        Oid relid)
{
    Relation rel;

    ScanKeyData skey;
    SysScanDesc scandesc;

    HeapTuple constuple;

    rel = heap_open(ConstraintRelationId, AccessShareLock);

    ScanKeyInit(&skey, Anum_pg_constraint_conrelid, BTEqualStrategyNumber,
            F_OIDEQ, ObjectIdGetDatum(relid));
    scandesc = systable_beginscan(rel, InvalidOid, FALSE, SnapshotNow, 1,
            &skey);
    constuple = systable_getnext(scandesc);
    while (constuple)
    {
        AddTupleWithToastsToContextInfo(cxt, ConstraintRelationId, "pg_constraint",
                constuple, MASTER_CONTENT_ID);
        constuple = systable_getnext(scandesc);
    }
    systable_endscan(scandesc);

    heap_close(rel, AccessShareLock);
}

/*
 * parse fast_sequence for dispatch
 */
static void
prepareDispatchedCatalogFastSequence(QueryContextInfo *cxt, Oid relid,
									 List *segnos)
{
}

/*
 * collect pg_class/pg_type/pg_attribute tuples for oid.
 * add them to in-memory heap table for dispatcher.
 */
void
prepareDispatchedCatalogSingleRelation(QueryContextInfo *cxt, Oid relid,
        bool forInsert, List *segnos)
{
    HeapTuple classtuple;

    Datum namespace, tablespace, toastrelid, relkind, relstorage, relname;

    Assert(relid != InvalidOid);

    /*
     * buildin object, dispatch nothing
     */
    if (relid < FirstNormalObjectId)
        return;

    if (alreadyAddedForDispatching(cxt->htab, relid, RelationType))
	{
        if (forInsert)
        {
            /*
             * We will be here whenever the same relation is used in
             * an INSERT clause and a FROM clause (GPSQL-872).
             */
            prepareDispatchedCatalogFastSequence(cxt, relid, segnos);
        }
        return;
    }

    /* find relid in pg_class */
    classtuple = SearchSysCache(RELOID, ObjectIdGetDatum(relid), 0, 0, 0);

    if (!HeapTupleIsValid(classtuple))
        elog(ERROR, "cache lookup failed for relation %u", relid);

    if (Debug_querycontext_print)
    {
        Form_pg_class tup = (Form_pg_class) GETSTRUCT(classtuple);

        elog(LOG, "Query Context: prepare object: relid = %u, relname = %s, "
                "relnamespace = %u, relfilenode = %u, relkind = %c",
                relid, tup->relname.data, tup->relnamespace,
                tup->relfilenode, tup->relkind);
    }

    AddTupleWithToastsToContextInfo(cxt, RelationRelationId, "pg_class", classtuple,
            MASTER_CONTENT_ID);

    /* collect pg_namespace info */
    namespace = SysCacheGetAttr(RELOID, classtuple, Anum_pg_class_relnamespace,
            NULL );

    if (InvalidOid == DatumGetObjectId(namespace))
        elog(ERROR, "relnamespace field in pg_class of %u is invalid", relid);

    prepareDispatchedCatalogNamespace(cxt, DatumGetObjectId(namespace));

    /* collect pg_tablespace info */
    tablespace = SysCacheGetAttr(RELOID, classtuple,
            Anum_pg_class_reltablespace, NULL );

    /* collect toast info */
    toastrelid = SysCacheGetAttr(RELOID, classtuple,
            Anum_pg_class_reltoastrelid, NULL );

    if (InvalidOid != DatumGetObjectId(toastrelid))
    {
        /*TODO*/
        Insist(!"cannot handle toast table right now!");
    }

    /* collect pg_type info */
    prepareDispatchedCatalogTypeByRelation(cxt, relid, classtuple);

    /* collect pg_attribute info */
    prepareDispatchedCatalogAttribute(cxt, relid);

    /* collect pg_attrdef info */
    /* Only INSERT statement will use column default value*/
    if(forInsert){
		prepareDispatchedCatalogAttributeDefault(cxt, relid);
    }
    /* collect pg_attribute_encoding info */
    prepareDispatchedCatalogAttributeEncoding(cxt, relid);

    /* collect pg_constraint info */
    prepareDispatchedCatalogConstraint(cxt, relid);

    relkind = SysCacheGetAttr(RELOID, classtuple, Anum_pg_class_relkind, NULL);

    relstorage = SysCacheGetAttr(RELOID, classtuple, Anum_pg_class_relstorage,
            NULL);

    relname = SysCacheGetAttr(RELOID, classtuple, Anum_pg_class_relname,
            NULL);

	/* The dfs tablespace oid must be dispatched. */
	if (DatumGetObjectId(tablespace) == InvalidOid && relstorage_is_ao(relstorage))
		prepareDispatchedCatalogTablespace(cxt, get_database_dts(MyDatabaseId));
	else
		prepareDispatchedCatalogTablespace(cxt, DatumGetObjectId(tablespace));

	switch (DatumGetChar(relstorage))
	{
	case RELSTORAGE_AOROWS:
	case RELSTORAGE_PARQUET:
		prepareDispatchedCatalogForAoParquet(cxt, relid, forInsert, segnos);
		break;
	case RELSTORAGE_EXTERNAL:
	    prepareDispatchedCatalogExternalTable(cxt, relid);
	    break;
	case RELSTORAGE_VIRTUAL:
	    break;
	case RELSTORAGE_HEAP:
	    /* support catalog tables (gp_dist_random et al.) */
	    break;

	case RELSTORAGE_FOREIGN:
	    /* TODO */
	    elog(ERROR, "not implemented relstorage: %c, relname: %s",
	            DatumGetChar(relstorage), DatumGetCString(relname));
	    break;
	default:
	    Insist(!"never get here");
	    break;
	}

    ReleaseSysCache(classtuple);
}

static Oid
getActiveSegrelid(Oid relid)
{
    Relation pg_appendonly_rel;
    TupleDesc pg_appendonly_dsc;
    HeapTuple tuple;
    ScanKeyData key;
    SysScanDesc aoscan;

    Oid retval;
    Datum temp;


    Snapshot saveSnapshot = ActiveSnapshot;
	ActiveSnapshot = CopySnapshot(ActiveSnapshot);
	ActiveSnapshot->curcid = GetCurrentCommandId();

    pg_appendonly_rel = heap_open(AppendOnlyRelationId, AccessShareLock);
    pg_appendonly_dsc = RelationGetDescr(pg_appendonly_rel);

    ScanKeyInit(&key, Anum_pg_appendonly_relid, BTEqualStrategyNumber, F_OIDEQ,
            ObjectIdGetDatum(relid));

    aoscan = systable_beginscan(pg_appendonly_rel, AppendOnlyRelidIndexId, TRUE,
            ActiveSnapshot, 1, &key);

    tuple = systable_getnext(aoscan);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT), errmsg("missing pg_appendonly"
                " entry for relation \"%s\"", get_rel_name(relid))));

    temp = heap_getattr(tuple, Anum_pg_appendonly_segrelid, pg_appendonly_dsc,
            NULL );

    retval = DatumGetObjectId(temp);

    /* Finish up scan and close pg_appendonly catalog. */
    systable_endscan(aoscan);

    heap_close(pg_appendonly_rel, AccessShareLock);

    /* Restore the old snapshot */
	ActiveSnapshot = saveSnapshot;

    return retval;
}

/*
 * parse pg_appendonly for dispatch
 */
static void
prepareDispatchedCatalogGpAppendOnly(QueryContextInfo *cxt,
        Oid relid, Oid *segrelid, Oid *segidxid)
{
    Relation pg_appendonly_rel;
    TupleDesc pg_appendonly_dsc;
    HeapTuple tuple;
    ScanKeyData key;
    SysScanDesc aoscan;

    Datum temp;

    /*
     * used to check if currently transaction can be serialized
     */
    Oid activeSegrelid = getActiveSegrelid(relid);

    /*
     * Check the pg_appendonly relation to be certain the ao table
     * is there.
     */
    pg_appendonly_rel = heap_open(AppendOnlyRelationId, AccessShareLock);
    pg_appendonly_dsc = RelationGetDescr(pg_appendonly_rel);

    ScanKeyInit(&key, Anum_pg_appendonly_relid, BTEqualStrategyNumber, F_OIDEQ,
            ObjectIdGetDatum(relid));

    aoscan = systable_beginscan(pg_appendonly_rel, AppendOnlyRelidIndexId, TRUE,
            SnapshotNow, 1, &key);

    tuple = systable_getnext(aoscan);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT), errmsg("missing pg_appendonly"
                " entry for relation \"%s\"", get_rel_name(relid))));

    AddTupleWithToastsToContextInfo(cxt, AppendOnlyRelationId, "pg_appendonly", tuple,
            MASTER_CONTENT_ID);

    temp = heap_getattr(tuple, Anum_pg_appendonly_segrelid, pg_appendonly_dsc,
            NULL );

    *segrelid = DatumGetObjectId(temp);

    if (*segrelid != activeSegrelid)
    {
    	/*
    	 * the pg_aoseg table for this relation is changed in other concurrent transaction,
    	 * it usually happened with a concurrent alter statement.
    	 * abort this transaction
    	 */
    	elog(ERROR, "could not serialize access due to read/write/alter dependencies among transactions");
    }

    temp = heap_getattr(tuple, Anum_pg_appendonly_segidxid, pg_appendonly_dsc,
            NULL );

    *segidxid = DatumGetObjectId(temp);

    if (Debug_querycontext_print)
    {
        elog(LOG, "Query Context: prepare pg_appendonly for rel = %u, "
                "segrelid = %u", relid, *segrelid);
    }

    /* Finish up scan and close pg_appendonly catalog. */
    systable_endscan(aoscan);

    heap_close(pg_appendonly_rel, AccessShareLock);

}

/*
 * parse AO relation range table and collect metadata used for QE
 * add them to in-memory heap table for dispatcher.
 */
static void
prepareDispatchedCatalogForAoParquet(QueryContextInfo *cxt, Oid relid,
        bool forInsert, List *segnos)
{

    Relation rel;
    Oid segrelid, segidxid;
    QueryContextDispatchingHashKey hkey;
    QueryContextDispatchingHashEntry *hentry = NULL;
    bool found;

    rel = heap_open(relid, AccessShareLock);

    Assert((RelationIsAoRows(rel) || RelationIsParquet(rel)));

    /*
     * add tuple in pg_appendonly
     */
    prepareDispatchedCatalogGpAppendOnly(cxt, RelationGetRelid(rel), &segrelid,
            &segidxid);

    Assert(segrelid != InvalidOid);

    hkey.objid = relid;
    hkey.type = RelationType;
    hentry = hash_search(cxt->htab, &hkey, HASH_FIND, &found);

    Assert(found);
    Assert(hentry);
    /*
     * Save pg_aoseg_* / pg_aocsseg_* relid in HTAB.  We may need it
     * later, e.g. to add gp_fastsequence tuple to dispatch context.
     * HTAB lookups are much faster than scanning pg_appendonly
     * catalog table.
     */
    hentry->aoseg_relid = segrelid;

    /*
     * add pg_aoseg_XXX/pg_paqseg_XXX's metadata
     */
    prepareDispatchedCatalogSingleRelation(cxt, segrelid, FALSE, 0);

	/*
	 * Although we have segrelid available here, we do not pass it to
	 * prepareDispatchedCatalogFastSequence().  We record it in hash
	 * table instead and look it up from the hash table inside the
	 * function.  This is redundant but necessary to be able to call
	 * this function from elsewhere.  This change is made as part of
	 * fix for GPSQL-872.
	 */
    if (forInsert)
        prepareDispatchedCatalogFastSequence(cxt, relid, segnos);

    heap_close(rel, AccessShareLock);
}

/*
 * parse AO/CO relation range table and collect metadata used for QE
 * add them to in-memory heap table for dispatcher.
 */
static void
prepareDispatchedCatalogExternalTable(QueryContextInfo *cxt,
        Oid relid)
{
    Relation pg_exttable_rel;
    TupleDesc pg_exttable_dsc;
    HeapTuple tuple;
    ScanKeyData key;
    SysScanDesc extscan;
	Datum *array;
	int array_size;
	char *location = NULL;

    Relation rel;

    rel = heap_open(relid, AccessShareLock);

    pg_exttable_rel = heap_open(ExtTableRelationId, RowExclusiveLock);
    pg_exttable_dsc = RelationGetDescr(pg_exttable_rel);

    ScanKeyInit(&key, Anum_pg_exttable_reloid, BTEqualStrategyNumber, F_OIDEQ,
            ObjectIdGetDatum(rel->rd_id));

    extscan = systable_beginscan(pg_exttable_rel, ExtTableReloidIndexId, true,
            SnapshotNow, 1, &key);

    tuple = systable_getnext(extscan);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT), errmsg("missing "
                "pg_exttable entry for relation \"%s\"", RelationGetRelationName(rel))));

	GetExtTableLocationsArray(tuple, pg_exttable_dsc,
							  &array, &array_size);

	location = GetExtTableFirstLocation(array);
	Insist(location != NULL);

	if (IS_PXF_URI(location))
	{
		Insist(array_size == 1);
		AddFileSystemCredentialForPxfTable();
		prepareDfsAddressForDispatch(cxt);
	}

	AddTupleWithToastsToContextInfo(cxt, ExtTableRelationId, "pg_exttable", tuple,
						  MASTER_CONTENT_ID);

    systable_endscan(extscan);

    heap_close(pg_exttable_rel, RowExclusiveLock);

    heap_close(rel, AccessShareLock);
}

static bool collect_func_walker(Node *node, QueryContextInfo *context)
{
	if (node == NULL)
		return false;

	if(IsA(node, SubPlan))
	{
		SubPlan *subplan = (SubPlan *) node;
		if (subplan->testexpr)
		{
			return expression_tree_walker(subplan->testexpr, collect_func_walker, context);
		}

		if (subplan->args)
		{
			expression_tree_walker((Node*) subplan->args, collect_func_walker, context);
		}
		
		return false;
	}

	if (IsA(node, Const))
	{
		/*
		 *When constants are part of the expression we should dispacth
		 *the type of the constant.
		 */
		Const *var = (Const *) node;
		prepareDispatchedCatalogType(context, var->consttype);
	}
 
	if (IsA(node, Var))
	{
		/*
		 * This handler is for user defined types.
		 * prepareDispatchedCatalogType() checks if the oid of this type
		 * is greater than FirstNormalObjectId so we do not need to test
		 * that here.
		 */
		Var *var = (Var *) node;
		prepareDispatchedCatalogType(context, var->vartype);
	}
	if (IsA(node, RowExpr))
	{
		/*
		 * RowExpr is ROW(x,y, ...).  It may appear as argument to a UDF
		 * in place of a composite type value.  E.g.
		 *
		 *    SELECT foo(ROW(x,y,z), ...) FROM ...
		 *
		 * Assumption: By the time we reach here, ROW() is mapped to the
		 * correct composite type given by RowExpr->row_typeid.
		 */  
		RowExpr *rowexpr = (RowExpr *) node;
		prepareDispatchedCatalogType(context, rowexpr->row_typeid);
		/* TODO: Should we return false from here? */
	}

	if (IsA(node, FuncExpr))
	{
		FuncExpr *func = (FuncExpr *) node;
		AclMode needAcl = ACL_NO_RIGHTS;
		switch (func->funcid)
		{
		case SETVAL_FUNC_OID:
			needAcl = ACL_UPDATE;
		case NEXTVAL_FUNC_OID:
			needAcl |= ACL_USAGE;
		{
			Const *arg;
			Oid seqoid;

			arg = (Const *) linitial(func->args);
			if (arg->xpr.type == T_Const && arg->consttype == REGCLASSOID)
			{
				seqoid = DatumGetObjectId(arg->constvalue);
            
				/* 
				 * aclchecks for nextval are done on the segments. But in HAWQ
				 * we are executing as bootstrap user on the segments. So any
				 * aclchecks on segments defeats the purpose.  Do the aclchecks
				 * on the master, prior to dispatch
				 */
				if (pg_class_aclcheck(seqoid, GetUserId(), needAcl) != ACLCHECK_OK)
					ereport(ERROR,
							(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
							 errmsg("permission denied for sequence %s",
									get_rel_name(seqoid))));
				prepareDispatchedCatalogSingleRelation(context,
													   seqoid, FALSE, 0);
			}
			else
			{
				ereport(ERROR, (errcode(ERRCODE_CDB_FEATURE_NOT_YET),
								errmsg("Non const argument in function "
								"\"NEXTVAL\" is not support yet.")));
			}
		}
        break;
		default:
			/* Check if this is a UDF*/
			if(func->funcid > FirstNormalObjectId)
			{
				/* do aclcheck on master, because HAWQ segments lacks user knowledge */
				AclResult aclresult;
				aclresult = pg_proc_aclcheck(func->funcid, GetUserId(), ACL_EXECUTE);
				if (aclresult != ACLCHECK_OK)
					aclcheck_error(aclresult, ACL_KIND_PROC, get_func_name(func->funcid));

				/* build the dispacth for the function itself */
				prepareDispatchedCatalogFunction(context, func->funcid);
			}
			/* Treat pg_database_size specially */
			else if (PgDatabaseSizeOidProcId == func->funcid || PgDatabaseSizeNameProcId == func->funcid)
			{
				/* dispatch all the table space information for calculating database size */
				prepareAllDispatchedCatalogTablespace(context);
			}
			break;
		}
		/* 
		 * Continue recursion in expression_tree_walker as arguments subtree may
		 * have FuncExpr's.  E.g. f(g() + h())
		 */
		return expression_tree_walker((Node *)func->args,
									  collect_func_walker, context);
	}
	if (IsA(node, Aggref))
	{
		Aggref *aggnode = (Aggref *) node;

		if (aggnode->aggorder != NULL)
		{
			ListCell	   *lc;

			foreach (lc, aggnode->aggorder->sortClause)
			{
				SortClause	   *sc = (SortClause *) lfirst(lc);

				prepareDispatchedCatalogOperator(context, sc->sortop);
			}
		}
		/*
		 * An aggregate has two catalog entries, one in pg_aggregate
		 * and the other in pg_proc.  Both need to be dispatched to
		 * segments.
		 */
		prepareDispatchedCatalogAggregate(context, aggnode->aggfnoid);
		prepareDispatchedCatalogFunction(context, aggnode->aggfnoid);
		return expression_tree_walker((Node *)aggnode->args,
									  collect_func_walker, context);
	}
	if (IsA(node, WindowRef))
	{
		/* 
		 * Window functions are nothing but aggregate functions
		 * invoked with "OVER(...)" clause.  Therefore, treat them as
		 * aggregates.
		 */
		WindowRef * wnode = (WindowRef *) node;
		prepareDispatchedCatalogAggregate(context, wnode->winfnoid);
		prepareDispatchedCatalogFunction(context, wnode->winfnoid);
		/*
		 * Should return type of the aggregate (window) function be
		 * included explicity?
		 */
		return expression_tree_walker((Node *)wnode->args,
									  collect_func_walker, context);
	}
	if (IsA(node, OpExpr))
	{
		OpExpr	   *op = (OpExpr *) node;

		if (OidIsValid(op->opfuncid))
			prepareDispatchedCatalogFunction(context, op->opfuncid);
		if (OidIsValid(op->opno))
			prepareDispatchedCatalogOperator(context, op->opno);
	}
	else if (IsA(node, RelabelType))
	{
		RelabelType	   *relable = (RelabelType *) node;

		prepareDispatchedCatalogType(context, relable->resulttype);
	}
	else if (IsA(node, ConvertRowtypeExpr))
	{
		ConvertRowtypeExpr	   *expr = (ConvertRowtypeExpr *) node;

		prepareDispatchedCatalogType(context, expr->resulttype);
	}
	else if (IsA(node, Sort))
	{
		Sort	   *sort = (Sort *) node;
		int			i;

		for (i = 0; i < sort->numCols; i++)
		{
			prepareDispatchedCatalogOperator(context, sort->sortOperators[i]);
		}
	}
	else if (IsA(node, SortClause))
	{
		SortClause	   *sc = (SortClause *) node;

		prepareDispatchedCatalogOperator(context, sc->sortop);
	}
	else if (IsA(node, GroupClause))
	{
		GroupClause	   *gc = (GroupClause *) node;

		prepareDispatchedCatalogOperator(context, gc->sortop);
	}

	return plan_tree_walker(node, collect_func_walker, context);
}

/*
Add the pg_authid tuple for the current user to the QueryContext
*/

static void
prepareDispatchedCatalogAuthUser(QueryContextInfo *cxt, Oid userOid)
{	
	HeapTuple authtuple;
	Assert(userOid != InvalidOid);

	/*
	* builtin object, dispatch nothing
	*/
	if (userOid < FirstNormalObjectId)
		return;

	if (alreadyAddedForDispatching(cxt->htab, userOid, ProcType))
		return;

	/* find user oid in pg_authid */
	cqContext  *pcqCtx;
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_authid "
								"WHERE oid = :1 ",
								ObjectIdGetDatum(userOid)));
	authtuple = caql_getnext(pcqCtx);
	if (!HeapTupleIsValid(authtuple))
		elog(ERROR, "pg_authid lookup failed for user %u", userOid);


	AddTupleToContextInfo(cxt, AuthIdRelationId, "pg_authid", authtuple, MASTER_CONTENT_ID);

	caql_endscan(pcqCtx);
}

/*
 * recursively scan the expression chain and collect function information
 */
static void
prepareDispatchedCatalogFunctionExpr(QueryContextInfo *cxt, Expr *expr)
{
    Assert(NULL != cxt && NULL != expr);
	collect_func_walker((Node *)expr, cxt);
}

static void
prepareDispatchedCatalogFunction(QueryContextInfo *cxt, Oid procOid)
{
	HeapTuple proctuple;
	Datum datum;
	Oid oidval;
	bool isNull = false;

    Assert(procOid != InvalidOid);

    /*   
     * buildin object, dispatch nothing
     */
    if (procOid < FirstNormalObjectId)
        return;

    if (alreadyAddedForDispatching(cxt->htab, procOid, ProcType))
        return;

    /* find relid in pg_class */
    cqContext  *pcqCtx;
    pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_proc "
								" WHERE oid = :1 ",
								ObjectIdGetDatum(procOid)));
	proctuple = caql_getnext(pcqCtx);
    if (!HeapTupleIsValid(proctuple))
        elog(ERROR, "cache lookup failed for proc %u", procOid);

	datum = caql_getattr(pcqCtx, Anum_pg_proc_prolang, &isNull);
	if (!isNull && datum)
	{
		oidval = DatumGetObjectId(datum);
		prepareDispatchedCatalogLanguage(cxt, oidval);
	}

	datum = caql_getattr(pcqCtx, Anum_pg_proc_pronamespace, &isNull);
	if (!isNull && datum)
	{
		oidval = DatumGetObjectId(datum);
		prepareDispatchedCatalogNamespace(cxt, oidval);
	}

	datum = caql_getattr(pcqCtx, Anum_pg_proc_prorettype, &isNull);
	if (!isNull && datum)
	{
		oidval = DatumGetObjectId(datum);
		prepareDispatchedCatalogType(cxt, oidval);
	}

	AddTupleWithToastsToContextInfo(cxt, ProcedureRelationId, "pg_proc", proctuple, MASTER_CONTENT_ID);

	caql_endscan(pcqCtx);
}

static void
prepareDispatchedCatalogLanguage(QueryContextInfo *ctx, Oid langOid)
{
	HeapTuple langtuple;

	Assert(langOid != InvalidOid);

	/*   
	 * buildin object, dispatch nothing
	 */
	if (langOid < FirstNormalObjectId)
		return;

	if (alreadyAddedForDispatching(ctx->htab, langOid, LangType))
		return;

	/* look up the tuple in pg_language */
	cqContext  *pcqCtx;
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_language "
								" WHERE oid = :1 ",
								ObjectIdGetDatum(langOid)));											
	langtuple = caql_getnext(pcqCtx);

	if (!HeapTupleIsValid(langtuple))
		elog(ERROR, "cache lookup failed for lang %u", langOid);				

	AddTupleWithToastsToContextInfo(ctx, LanguageRelationId, "pg_language", langtuple, MASTER_CONTENT_ID);	

	/* dispatch the language handler function*/
	bool lang_handler_isNull = false;
	Datum lang_handler_Datum = caql_getattr(pcqCtx, Anum_pg_language_lanplcallfoid, &lang_handler_isNull);
	if (!lang_handler_isNull && lang_handler_Datum)	
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(lang_handler_Datum));
	}


	caql_endscan(pcqCtx);			
}

static void
prepareDispatchedCatalogType(QueryContextInfo *ctx, Oid typeOid)
{
	HeapTuple typetuple;
	bool isNull = false;
	Datum typeDatum = 0;

	Assert(typeOid != InvalidOid);

	/*
	 * buildin object, dispatch nothing
	 */
	if (typeOid < FirstNormalObjectId)
		return;

	if (alreadyAddedForDispatching(ctx->htab, typeOid, TypeType))
		return;

	/* look up the tuple in pg_type */
	cqContext  *pcqCtx;
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_type "
								" WHERE oid = :1 ",
								ObjectIdGetDatum(typeOid)));
	typetuple = caql_getnext(pcqCtx);

	if (!HeapTupleIsValid(typetuple))
		elog(ERROR, "cache lookup failed for type %u", typeOid);

	/*
	 * In case of arrays of user defined types we should also
	 * dispatch the underlying type defined by typelem attribute
	 * if it is also a user defined type.
	 */
	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typelem, &isNull);
	if (!isNull && OidIsValid(DatumGetObjectId(typeDatum)))
	{
		prepareDispatchedCatalogType(ctx, DatumGetObjectId(typeDatum));
	}

	/*
	 * We need to dispatch all the accompanying functions for user defined types.
	 */
	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typinput, &isNull);
	if (!isNull && OidIsValid(DatumGetObjectId(typeDatum)))
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(typeDatum));
	}

	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typoutput, &isNull);
	if (!isNull && OidIsValid(DatumGetObjectId(typeDatum)))
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(typeDatum));
	}

	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typreceive, &isNull);
	if (!isNull && OidIsValid(DatumGetObjectId(typeDatum)))
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(typeDatum));
	}

	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typsend, &isNull);
	if (!isNull && OidIsValid(DatumGetObjectId(typeDatum)))
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(typeDatum));
	}

	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typreceive, &isNull);
	if (!isNull && typeDatum)
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(typeDatum));
	}

	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typsend, &isNull);
	if (!isNull && typeDatum)
	{
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(typeDatum));
	}

	AddTupleWithToastsToContextInfo(ctx, TypeRelationId, "pg_type", typetuple,
						  MASTER_CONTENT_ID);

	/*
	 * ROW(f1, f2, ...) expression may not have corresponding pg_type
	 * tuple and related metadata included in the context.  If it is
	 * already included, the following is a no-op.
	 */
	typeDatum = caql_getattr(pcqCtx, Anum_pg_type_typrelid, &isNull);
    if (!isNull && OidIsValid(DatumGetObjectId(typeDatum)))
	{
		prepareDispatchedCatalogSingleRelation(ctx, DatumGetObjectId(typeDatum),
											   FALSE, 0);
	}

	caql_endscan(pcqCtx);

	/*
	 * For user defined types we also dispatch associated operator classes.
	 * This is to safe guard against certain cases like Sort Operator and
	 * Hash Aggregates where the plan tree does not explicitly contain all the
	 * operators that might be needed by the executor on the segments.
	 */
	prepareDispatchedCatalogOpClassForType(ctx, typeOid);
}

/* For user defined type dispatch the operator class. */
static void
prepareDispatchedCatalogOpClassForType(QueryContextInfo *ctx, Oid typeOid)
{
	cqContext      *pcqCtx;
	HeapTuple       tuple;
	Datum           value;

	if (!OidIsValid(typeOid))
		return;

	/*
	 * builtin object, dispatch nothing.
	 */
	if (typeOid < FirstNormalObjectId)
		return;

	pcqCtx = caql_beginscan(NULL,
							cql("SELECT oid FROM pg_opclass"
								" WHERE opcintype = :1",
								ObjectIdGetDatum(typeOid)));

	while (HeapTupleIsValid(tuple = caql_getnext(pcqCtx)))
	{
		value = HeapTupleGetOid(tuple);
		if (OidIsValid(DatumGetObjectId(value)))
			prepareDispatchedCatalogOpClass(ctx, DatumGetObjectId(value));
	}

	caql_endscan(pcqCtx);
}

/*
 * This function does not do the actual work. It checks if
 * there is an operator class associated with this operator and
 * if found delegates the work to prepareDispatchedOpClass else
 * delegates work to addOperatorToDispatchContext.
 */
static void
prepareDispatchedCatalogOperator(QueryContextInfo *ctx, Oid opOid)
{
	cqContext	   *pcqCtx;
	bool			isnull;
	bool			foundOperatorClass = false;

	/*
	 * builtin object, dispatch nothing.
	 */
	if (opOid < FirstNormalObjectId)
		return;

	if (alreadyAddedForDispatching(ctx->htab, opOid, OpType))
		return;

	/*
	 * Check if we have an operator class associated with this operator.
	 * If yes, the prepareDispatchedOpClass will handle adding this operator
	 * to the context.
	 */
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_amop"
								" WHERE amopopr = :1",
								ObjectIdGetDatum(opOid)));
	while (HeapTupleIsValid(caql_getnext(pcqCtx)))
	{
		foundOperatorClass = true;
		Oid		opclass;
		opclass = DatumGetObjectId(
				caql_getattr(pcqCtx, Anum_pg_amop_amopclaid, &isnull));

		prepareDispatchedCatalogOpClass(ctx, opclass);
	}

	caql_endscan(pcqCtx);

	/*
	 * Otherwise, call addOperatorToDispatchContext to add this operator from
	 * here and bail out.
	 */
	if (!foundOperatorClass)
	{
		addOperatorToDispatchContext(ctx, opOid);
	}
}

/* just add the pg_operator tuple and associated operator functions */
static void
addOperatorToDispatchContext(QueryContextInfo *ctx, Oid opOid)
{
	cqContext	   *pcqCtx;
	HeapTuple		tuple;
	Datum			value;
	bool			isnull;

	/*
	 * builtin object, dispatch nothing.
	 */
	if (opOid < FirstNormalObjectId)
		return;

	if (alreadyAddedForDispatching(ctx->htab, opOid, OpType))
		return;

	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_operator"
								" WHERE oid = :1",
								ObjectIdGetDatum(opOid)));
	tuple = caql_getnext(pcqCtx);
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for operator %u", opOid);

	AddTupleToContextInfo(ctx, OperatorRelationId, "pg_operator", tuple,
						  MASTER_CONTENT_ID);

	value = caql_getattr(pcqCtx, Anum_pg_operator_oprcode, &isnull);
	if (!isnull && OidIsValid(DatumGetObjectId(value)))
		prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(value));

	/* sort operators */
	value = caql_getattr(pcqCtx, Anum_pg_operator_oprlsortop, &isnull);
	if (!isnull && OidIsValid(DatumGetObjectId(value)))
		addOperatorToDispatchContext(ctx, DatumGetObjectId(value));

	value = caql_getattr(pcqCtx, Anum_pg_operator_oprrsortop, &isnull);
	if (!isnull && OidIsValid(DatumGetObjectId(value)))
		addOperatorToDispatchContext(ctx, DatumGetObjectId(value));

	/* merge join LT compare operator */
	value = caql_getattr(pcqCtx, Anum_pg_operator_oprltcmpop, &isnull);
	if (!isnull && OidIsValid(DatumGetObjectId(value)))
	{
		Oid		ltproc;

		ltproc = get_opcode(DatumGetObjectId(value));
		if (OidIsValid(ltproc))
			prepareDispatchedCatalogFunction(ctx, ltproc);
	}

	/* merge join GT compare operator */
	value = caql_getattr(pcqCtx, Anum_pg_operator_oprgtcmpop, &isnull);
	if (!isnull && OidIsValid(DatumGetObjectId(value)))
	{
		Oid		gtproc;

		gtproc = get_opcode(DatumGetObjectId(value));
		if (OidIsValid(gtproc))
			prepareDispatchedCatalogFunction(ctx, gtproc);
	}

	caql_endscan(pcqCtx);
}

/*
 * For opclass, we dispatch pg_opclass, pg_amproc, and pg_amop tuples.
 * Loop through all the underlying operators and dispatch them too.
 */
static void
prepareDispatchedCatalogOpClass(QueryContextInfo *ctx, Oid opclass)
{
	cqContext	   *pcqCtx;
	HeapTuple		tuple;
	Datum			value;
	bool			isnull;

	/*
	 * builtin object, dispatch nothing.
	 */
	if (!OidIsValid(opclass))
		return;

	if (opclass < FirstNormalObjectId)
		return;

	if (alreadyAddedForDispatching(ctx->htab, opclass, OpClassType))
		return;

	/* pg_opclass */
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_opclass"
								" WHERE oid = :1",
								ObjectIdGetDatum(opclass)));
	tuple = caql_getnext(pcqCtx);
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for operator class %u", opclass);

	AddTupleToContextInfo(ctx, OperatorClassRelationId, "pg_opclass",
						  tuple, MASTER_CONTENT_ID);

	caql_endscan(pcqCtx);

	/* pg_amproc */
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_amproc"
								" WHERE amopclaid = :1",
								ObjectIdGetDatum(opclass)));

	while (HeapTupleIsValid(tuple = caql_getnext(pcqCtx)))
	{
		AddTupleToContextInfo(ctx, AccessMethodProcedureRelationId,
							  "pg_amproc", tuple, MASTER_CONTENT_ID);

		value = caql_getattr(pcqCtx, Anum_pg_amproc_amproc, &isnull);
		if (!isnull && OidIsValid(DatumGetObjectId(value)))
			prepareDispatchedCatalogFunction(ctx, DatumGetObjectId(value));
	}

	caql_endscan(pcqCtx);

	/* pg_amop and dispatch all underlying operators */
	/*
	 * Ordinary operator expression does not need anything than underlying
	 * function, but in case of HJ, we need hash function information too.
	 * Since it's almost impossible to know if this operator is used for HJ
	 * or others, we just send everything that might be needed.
	 */
	pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_amop"
								" WHERE amopclaid = :1",
								ObjectIdGetDatum(opclass)));

	while (HeapTupleIsValid(tuple = caql_getnext(pcqCtx)))
	{
		AddTupleToContextInfo(ctx, AccessMethodOperatorRelationId, "pg_amop",
							  tuple, MASTER_CONTENT_ID);
		value = caql_getattr(pcqCtx, Anum_pg_amop_amopopr, &isnull);
		if (!isnull && OidIsValid(DatumGetObjectId(value)))
		{
			addOperatorToDispatchContext(ctx, DatumGetObjectId(value));
		}
	}

	caql_endscan(pcqCtx);
}

static void
prepareDispatchedCatalogAggregate(QueryContextInfo *cxt, Oid aggfuncoid)
{
	HeapTuple aggtuple;
	bool isNull = false;
	Datum procDatum = 0;

    Assert(aggfuncoid != InvalidOid);

    /*
     * buildin object, dispatch nothing
     */
    if (aggfuncoid < FirstNormalObjectId)
        return;

    if (alreadyAddedForDispatching(cxt->htab, aggfuncoid, AggType))
        return;

    /* find relid in pg_class */
    cqContext  *pcqCtx;
    pcqCtx = caql_beginscan(NULL,
							cql("SELECT * FROM pg_aggregate "
								" WHERE aggfnoid = :1 ",
								ObjectIdGetDatum(aggfuncoid)));
	aggtuple = caql_getnext(pcqCtx);
    if (!HeapTupleIsValid(aggtuple))
        elog(ERROR, "cache lookup failed for aggregate %u", aggfuncoid);

	/*
	 * Include all possible pg_proc tuples in query context this
	 * aggregate may refer to.  Excluding agginvtransfn and
	 * agginvprelimfn because they are not put to any use anywhere in
	 * the codebase.
	 */
	procDatum = caql_getattr(pcqCtx, Anum_pg_aggregate_aggtransfn, &isNull);
	if (!isNull && procDatum)
	{
		prepareDispatchedCatalogFunction(cxt, DatumGetObjectId(procDatum));
	}
	procDatum = caql_getattr(pcqCtx, Anum_pg_aggregate_aggprelimfn, &isNull);
	if (!isNull && procDatum)
	{
		prepareDispatchedCatalogFunction(cxt, DatumGetObjectId(procDatum));
	}
	procDatum = caql_getattr(pcqCtx, Anum_pg_aggregate_aggfinalfn, &isNull);
	if (!isNull && procDatum)
	{
		prepareDispatchedCatalogFunction(cxt, DatumGetObjectId(procDatum));
	}

	AddTupleWithToastsToContextInfo(cxt, AggregateRelationId, "pg_aggregate",
						  aggtuple, MASTER_CONTENT_ID);
	caql_endscan(pcqCtx);
}

static List *
findSegnofromMap(Oid relid, List *segnoMaps)
{
	ListCell *relid_to_segno;
	List *mysegnos = NIL;

	foreach(relid_to_segno, segnoMaps)
	{
		SegfileMapNode *n = (SegfileMapNode *) lfirst(relid_to_segno);

		if (n->relid == relid)
		{
			Assert(n->segnos != NIL);
			mysegnos = n->segnos;
			break;
		}
	}
	return mysegnos;
}

/*
 * parse Relation and collect metadata used for QE add them to in-memory heap
 * table for dispatcher.
 */
void
prepareDispatchedCatalogRelation(QueryContextInfo *cxt, Oid relid,
        bool forInsert, List *segnoMaps)
{
    List *children = NIL;
    ListCell *child;

    if (rel_is_partitioned(relid))
    {
        children = find_all_inheritors(relid);
        foreach(child, children)
        {
            Oid myrelid = lfirst_oid(child);
            if (forInsert)
            {
				List *mysegnos = findSegnofromMap(myrelid, segnoMaps);
                Assert(mysegnos != NIL);
                prepareDispatchedCatalogSingleRelation(cxt, myrelid, TRUE,
                        mysegnos);

            }
            else
            {
                prepareDispatchedCatalogSingleRelation(cxt, myrelid, FALSE, 0);
            }
        }
        list_free(children);
    }
    else
    {
        if (forInsert && NULL != segnoMaps)
        {
            List *mysegnos = findSegnofromMap(relid, segnoMaps);

            Assert(mysegnos != NIL);
            prepareDispatchedCatalogSingleRelation(cxt, relid, TRUE, mysegnos);
        }
        else
        {
            prepareDispatchedCatalogSingleRelation(cxt, relid, FALSE, 0);
        }
    }
}

/*
 * parse target list to handle function.
 */
void
prepareDispatchedCatalogTargets(QueryContextInfo *cxt, List *targets)
{
    ListCell *lc;
    Assert(NULL != targets);
    Assert(NULL != cxt);

    foreach(lc, targets)
    {
        TargetEntry *te = lfirst(lc);

        if (te->resjunk)
            continue;

        if (te->expr)
            prepareDispatchedCatalogFunctionExpr(cxt, te->expr);
    }
}

/*
 * parse plan for some functions in plan's targets.
 */
void
prepareDispatchedCatalogPlan(QueryContextInfo *cxt, Plan *plan)
{
    if (!plan)
        return;

    Assert(NULL != cxt);
	/*
	Add session user pg_authid tuple to the context
	*/
	prepareDispatchedCatalogAuthUser(cxt, GetSessionUserId());

    collect_func_walker((Node *)plan, cxt);
}

/*
 * parse range table and collect metadata used for QE,
 * add them to in-memory heap table for dispatcher.
 */
void
prepareDispatchedCatalog(QueryContextInfo *cxt, List *rtable)
{
    ListCell *lc;

    Assert(NULL != rtable);
    Assert(NULL != cxt);

    foreach(lc, rtable)
    {
        RangeTblEntry *rte = lfirst(lc);
        switch (rte->rtekind)
        {
        case RTE_RELATION:             /*ordinary relation reference */
            /*
             * Relations in range table are already included by calls to
             * prepareDispatchedCatalogRelation from ExecutorStart().
             */
            break;

        case RTE_FUNCTION:             /*function in FROM */
            if (rte->funcexpr)
                    prepareDispatchedCatalogFunctionExpr(cxt, (Expr *)rte->funcexpr);
            break;

        case RTE_SUBQUERY:             /*subquery in FROM */
            if (rte->subquery)
            {
                List *sub_rtable = rte->subquery->rtable;
                List *sub_targets = rte->subquery->targetList;
                if (sub_rtable)
                    prepareDispatchedCatalog(cxt, sub_rtable);
                if (sub_targets)
                    prepareDispatchedCatalogTargets(cxt, sub_targets);
            }
            break;

        case RTE_VALUES:               /*VALUES (<exprlist>), (<exprlist>): ... */
            if (rte->values_lists)
            {
                ListCell *lc;

                foreach(lc, rte->values_lists)
                {
                    List *exprs = lfirst(lc);

                    if (exprs)
                    {
                        ListCell *cell;

                        foreach(cell, rte->values_lists)
                        {
                            Expr *expr = lfirst(cell);

                            prepareDispatchedCatalogFunctionExpr(cxt, expr);
                        }
                    }
                }
            }
            break;

        case RTE_JOIN:                 /*join */
        case RTE_VOID:                 /*CDB: deleted RTE */
            break;

        case RTE_SPECIAL:              /*special rule relation (NEW or OLD) */
            elog(ERROR, "dispatch metedata for RTE_SPECIAL node is not implemented");
            break;
        case RTE_CTE:                   /*CommonTableExpr in FROM */
            /* nothing to do for cte */
            break;
        case RTE_TABLEFUNCTION:        /*CDB: Functions over multiset input */
            /*TODO */
            elog(ERROR, "dispatch metedata for RTE_TABLEFUNCTION node is not implemented");
            break;
        default:
            Insist(!"never get here");
            break;
        }
    }
}

/*
 * create a hash table used to filter out the duplicated table
 */
HTAB *
createPrepareDispatchedCatalogRelationDisctinctHashTable(void)
{
    HASHCTL info;
    HTAB *rels = NULL;

    MemSet(&info, 0, sizeof(info));

    info.hash = tag_hash;
    info.keysize = sizeof(QueryContextDispatchingHashKey);
    info.entrysize = sizeof(QueryContextDispatchingHashEntry);

    rels = hash_create("all relations", 10, &info, HASH_FUNCTION | HASH_ELEM);

    return rels;
}

QueryContextDispatchingSendBack
CreateQueryContextDispatchingSendBack(int nfile)
{
	QueryContextDispatchingSendBack rc =
			palloc0(sizeof(struct QueryContextDispatchingSendBackData));
	rc->numfiles = nfile;
	rc->eof = palloc0(nfile * sizeof(int64));
	rc->uncompressed_eof = palloc0(nfile * sizeof(int64));

	return rc;
}

void
DropQueryContextDispatchingSendBack(QueryContextDispatchingSendBack sendback)
{
	if (sendback)
	{
		if (sendback->eof)
			pfree(sendback->eof);
		if (sendback->uncompressed_eof)
			pfree(sendback->uncompressed_eof);
		pfree(sendback);
	}
}


void
UpdateCatalogModifiedOnSegments(QueryContextDispatchingSendBack sendback)
{
	Assert(NULL != sendback);

	AppendOnlyEntry *aoEntry = GetAppendOnlyEntry(sendback->relid, SnapshotNow);
	Assert(aoEntry != NULL);

	Relation rel = heap_open(sendback->relid, AccessShareLock);
	if (RelationIsAoRows(rel))
	{
		Insist(sendback->numfiles == 1);
		UpdateFileSegInfo(rel, aoEntry, sendback->segno,
				sendback->eof[0], sendback->uncompressed_eof[0], sendback->insertCount,
				sendback->varblock);
	}
	else if (RelationIsParquet(rel))
	{
		Insist(sendback->numfiles == 1);
		UpdateParquetFileSegInfo(rel, aoEntry, sendback->segno,
				sendback->eof[0], sendback->uncompressed_eof[0], sendback->insertCount);
	}

	heap_close(rel, AccessShareLock);

	/*
	 * make the change available
	 */
	CommandCounterIncrement();
}

StringInfo
PreSendbackChangedCatalog(int aocount)
{
	StringInfo buf = makeStringInfo();

	pq_beginmessage(buf, 'h');

	/*
	 * 2, send number of relations
	 */
	pq_sendint(buf, aocount, 4);

	return buf;
}

void
AddSendbackChangedCatalogContent(StringInfo buf,
		QueryContextDispatchingSendBack sendback)
{
	int i;

	/*
	 * 3, send relation id
	 */
	pq_sendint(buf, sendback->relid, 4);
	/*
	 * 4, send insertCount
	 */
	pq_sendint64(buf, sendback->insertCount);

	/*
	 * 5, send segment file no.
	 */
	pq_sendint(buf, sendback->segno, 4);
	/*
	 * 6, send varblock count
	 */
	pq_sendint64(buf, sendback->varblock);

	/*
	 * 7, send number of files
	 */
	pq_sendint(buf, sendback->numfiles, 4);

	for (i = 0; i < sendback->numfiles; ++i)
	{
		/*
		 * 8, send eof
		 */
		pq_sendint64(buf, sendback->eof[i]);
		/*
		 * 9 send uncompressed eof
		 */
		pq_sendint64(buf, sendback->uncompressed_eof[i]);
	}

}


void
FinishSendbackChangedCatalog(StringInfo buf)
{
	pq_endmessage(buf);
	pfree(buf);
}

static void GetExtTableLocationsArray(HeapTuple tuple,
									  TupleDesc exttab_desc,
									  Datum **array,
									  int *array_size)
{
	Datum locations;
	bool isNull = false;

	locations = heap_getattr(tuple,
							 Anum_pg_exttable_location,
							 exttab_desc,
							 &isNull);
	Insist(!isNull);

	deconstruct_array(DatumGetArrayTypeP(locations),
					  TEXTOID, -1, false, 'i',
					  array, NULL, array_size);
	Insist(*array_size > 0);
}

static char* GetExtTableFirstLocation(Datum *array)
{
	return DatumGetCString(DirectFunctionCall1(textout, array[0]));
}

/* 
 * Using HAWQ's HDFS location, dispatch HDFS credentials to
 * segments.
 *
 * The function uses a hdfs uri in the form hdfs://host:port/path
 * or hdfs://nameservice/path where
 * this value is taken from pg_filespace_entry which is populated
 * based on hawq-site.xml's hawq_dfs_url entry.
 *
 * prepareDispatchedCatalogFileSystemCredential will store the token
 * using port == 0 in HA case (otherwise the supplied port).
 */
static void AddFileSystemCredentialForPxfTable()
{
	char* dfs_address = NULL;

	if (!enable_secure_filesystem)
		return;

	get_hdfs_location_from_filespace(&dfs_address);

    elog(DEBUG2, "about to acquire delegation token for %s", dfs_address);

	prepareDispatchedCatalogFileSystemCredential(dfs_address);

	pfree(dfs_address);
}

List *
fetchSegFileInfos(Oid relid, List *segnos)
{
	List *result = NIL;
	if ((segnos != NIL) && (list_length(segnos) > 0))
	{
		ListCell *lc;
		char storageChar;
		AppendOnlyEntry *aoEntry = NULL;

		foreach (lc, segnos)
		{
			int segno = lfirst_int(lc);
			ResultRelSegFileInfo *segfileinfo = makeNode(ResultRelSegFileInfo);
			segfileinfo->segno = segno;
			result = lappend(result, segfileinfo);
		}

		storageChar = get_relation_storage_type(relid);
		/*
		 * Get pg_appendonly information for this table.
		 */
		aoEntry = GetAppendOnlyEntry(relid, SnapshotNow);

		/*
		 * Based on the pg_appendonly information, fetch
		 * the segment file information associated with
		 * this relation and this segno.
		 */
		if (RELSTORAGE_AOROWS == storageChar)
		{
			AOFetchSegFileInfo(aoEntry, result, SnapshotNow);
		}
		else
		{
			Assert(RELSTORAGE_PARQUET == storageChar);
			ParquetFetchSegFileInfo(aoEntry, result, SnapshotNow);
		}
	}
	return result;
}

static ResultRelSegFileInfoMapNode *
fetchSegFileInfoMapNode(Oid relid, List *segnos)
{
	ResultRelSegFileInfoMapNode *result = makeNode(ResultRelSegFileInfoMapNode);

	result->relid = relid;
	result->segfileinfos = fetchSegFileInfos(relid, segnos);

	return result;
}

/*
 * GetResultRelSegFileInfos
 *
 * Given the relid and its segnos for the result relation,
 * fetch the segment file infomation associated those
 * segment number.
 */
List *
GetResultRelSegFileInfos(Oid relid, List *segnomaps, List *existing_seginfomaps)
{
	ResultRelSegFileInfoMapNode *result = NULL;

	if (rel_is_partitioned(relid))
	{
		List *children = NIL;
		ListCell *child;
		children = find_all_inheritors(relid);
		foreach (child, children)
		{
			Oid myrelid = lfirst_oid(child);
			List *mysegnos = findSegnofromMap(myrelid, segnomaps);
			result = fetchSegFileInfoMapNode(myrelid, mysegnos);
			existing_seginfomaps = lappend(existing_seginfomaps, result);
		}
		list_free(children);
	}
	else
	{
		List *mysegnos = findSegnofromMap(relid, segnomaps);
		result = fetchSegFileInfoMapNode(relid, mysegnos);
		existing_seginfomaps = lappend(existing_seginfomaps, result);
	}

	return existing_seginfomaps;
}

/*
 * prepareDfsAddressForDispatch
 *
 * Given the cxt use the currently set value of cxt->sharedPath
 * and add it to cxt->buffer so that it is dispatched from
 * master to segment. This is only required in the case of
 * a secure filesystem.
 */

static void
prepareDfsAddressForDispatch(QueryContextInfo* cxt)
{
	if (!enable_secure_filesystem)
		return;
	const char *namespace = cxt->sharedPath;
	elog(DEBUG2, "*********************** MASTER SHARED PATH VALUE %s *********************", cxt->sharedPath);
	/*
	 * Need to account for '\0' when dispatching length
	 */
	int size = strlen(namespace) + 1;
	StringInfoData buffer;
	initStringInfo(&buffer);

	pq_sendint(&buffer, (int) Namespace, sizeof(char));
	pq_sendint(&buffer, size, sizeof(int));

	WriteData(cxt, buffer.data, buffer.len);
	WriteData(cxt, namespace, size);
	pfree(buffer.data);
}