src/include/access/appendonlytid.h

/*-------------------------------------------------------------------------
 *
 * appendonlystoragetid.h
 *
 * 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.
 *
 *-------------------------------------------------------------------------
 */
#ifndef APPENDONLYTID_H
#define APPENDONLYTID_H

#include "c.h"

/* 
 * AOTupleId is a unique tuple id, specific to AO 
 * relation tuples, of the form (segfile#, row#)
 * 
 * *** WARNING *** Some code interprets AOTIDs as HEAPTIDs, and would like
 * AOTIDs has the same ordering as HEAPTIDs.
 *
 * Begin mischief.  Want to make sure the last 16 bits (uint16) are non-zero so that when
 * the executor asserts the item number is non-zero our AOTID will pass the test.
 * So, we create a reserved bit that is always on.  So, in the case that the segment file
 * number is 0 (utility mode) and the lower part (15 bits) of the row number is 0, our AOTID's
 * last 16 bits will be non-zero because of the always on reserved bit.
 *
 * Out of the following 48 bits, the 7 leftmost bits stand for which segment file the
 * tuple is in (Limit: 128 (2^8)), the 16th rightmost bit is reserved and always 1, 
 * the remaining 40 bits stand for the row within the  segment file
 * (Limit: 1099 trillion (2^40 - 1)).
 *
 *
 * ***WARNING*** STRUCT PACKING ISSUE.
 *
 *       Previously, we had the uint16 first and the uint32 second.  But on some compliers
 *       the second uint32 would get packed on a 32-bit boundary and the struct would end
 *       up with a hole between the fields...  Arranging the uint16 second is known to work
 *       correctly since the ItemPointerData has the same layout.  And, apparently putting
 *       small fields after big ones is a policy in system catalog struct layouts.
 */
typedef struct AOTupleId
{
	uint16      bytes_0_1;
	uint16		bytes_2_3;
	uint16		bytes_4_5;

} AOTupleId;

#define AOTUPLEID_INIT {0,0}
   
#define AOTupleIdGet_segmentFileNum(h)        ((((h)->bytes_0_1&0xFE00)>>9)) // 7 bits
#define AOTupleIdGet_makeHeapExecutorHappy(h) (((h)->bytes_4_5&0x8000)) // 1 bit
#define AOTupleIdGet_rowNum(h) \
	((((uint64)((h)->bytes_0_1&0x01FF))<<31)|(((uint64)((h)->bytes_2_3))<<15)|(((uint64)((h)->bytes_4_5&0x7FFF))))
         /* top most 25 bits */           /* 15 bits from bytes_4_5 */

/* ~_Init zeroes the 2 regular fields and sets the always on field to 1. */
#define AOTupleIdInit_Init(h)                {(h)->bytes_0_1=0;(h)->bytes_2_3=0;(h)->bytes_4_5=0x8000;}
#define AOTupleIdInit_segmentFileNum(h,e)    {(h)->bytes_0_1|=(((uint16)(0x007F&((uint16)(e))))<<9);}
#define AOTupleIdInit_rowNum(h,e)            {(h)->bytes_0_1|=((uint16)((INT64CONST(0x000000FFFFFFFFFF)&(e))>>31));\
											  (h)->bytes_2_3|=((uint16)((INT64CONST(0x000000007FFFFFFF)&(e))>>15));\
											  (h)->bytes_4_5|=((0x7FFF&((uint16)(e))));}

#define AOTupleId_MaxRowNum            INT64CONST(1099511627775) 		// 40 bits, or 1099511627775 (1099 trillion).
#define AOTupleId_MaxRowNum_CommaStr  "1,099,511,627,775"

#define AOTupleId_MaxSegmentFileNum    			127
#define AOTupleId_MultiplierSegmentFileNum    	128	// Next up power of 2 as multiplier.

extern char* AOTupleIdToString(AOTupleId * aoTupleId);

#endif   /* APPENDONLYTID_H */