src/backend/utils/adt/uuid.c

/*-------------------------------------------------------------------------
 *
 * uuid.c
 *	  Functions for the built-in type "uuid".
 *
 * Copyright (c) 2007-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/backend/utils/adt/uuid.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "common/hashfn.h"
#include "lib/hyperloglog.h"
#include "libpq/pqformat.h"
#include "port/pg_bswap.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/sortsupport.h"
#include "utils/uuid.h"

/* sortsupport for uuid */
typedef struct
{
	int64		input_count;	/* number of non-null values seen */
	bool		estimating;		/* true if estimating cardinality */

	hyperLogLogState abbr_card; /* cardinality estimator */
} uuid_sortsupport_state;

static void string_to_uuid(const char *source, pg_uuid_t *uuid);
static int	uuid_internal_cmp(const pg_uuid_t *arg1, const pg_uuid_t *arg2);
static int	uuid_fast_cmp(Datum x, Datum y, SortSupport ssup);
static int	uuid_cmp_abbrev(Datum x, Datum y, SortSupport ssup);
static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup);
static Datum uuid_abbrev_convert(Datum original, SortSupport ssup);

Datum
uuid_in(PG_FUNCTION_ARGS)
{
	char	   *uuid_str = PG_GETARG_CSTRING(0);
	pg_uuid_t  *uuid;

	uuid = (pg_uuid_t *) palloc(sizeof(*uuid));
	string_to_uuid(uuid_str, uuid);
	PG_RETURN_UUID_P(uuid);
}

Datum
uuid_out(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *uuid = PG_GETARG_UUID_P(0);
	static const char hex_chars[] = "0123456789abcdef";
	StringInfoData buf;
	int			i;

	initStringInfo(&buf);
	for (i = 0; i < UUID_LEN; i++)
	{
		int			hi;
		int			lo;

		/*
		 * We print uuid values as a string of 8, 4, 4, 4, and then 12
		 * hexadecimal characters, with each group is separated by a hyphen
		 * ("-"). Therefore, add the hyphens at the appropriate places here.
		 */
		if (i == 4 || i == 6 || i == 8 || i == 10)
			appendStringInfoChar(&buf, '-');

		hi = uuid->data[i] >> 4;
		lo = uuid->data[i] & 0x0F;

		appendStringInfoChar(&buf, hex_chars[hi]);
		appendStringInfoChar(&buf, hex_chars[lo]);
	}

	PG_RETURN_CSTRING(buf.data);
}

/*
 * We allow UUIDs as a series of 32 hexadecimal digits with an optional dash
 * after each group of 4 hexadecimal digits, and optionally surrounded by {}.
 * (The canonical format 8x-4x-4x-4x-12x, where "nx" means n hexadecimal
 * digits, is the only one used for output.)
 */
static void
string_to_uuid(const char *source, pg_uuid_t *uuid)
{
	const char *src = source;
	bool		braces = false;
	int			i;

	if (src[0] == '{')
	{
		src++;
		braces = true;
	}

	for (i = 0; i < UUID_LEN; i++)
	{
		char		str_buf[3];

		if (src[0] == '\0' || src[1] == '\0')
			goto syntax_error;
		memcpy(str_buf, src, 2);
		if (!isxdigit((unsigned char) str_buf[0]) ||
			!isxdigit((unsigned char) str_buf[1]))
			goto syntax_error;

		str_buf[2] = '\0';
		uuid->data[i] = (unsigned char) strtoul(str_buf, NULL, 16);
		src += 2;
		if (src[0] == '-' && (i % 2) == 1 && i < UUID_LEN - 1)
			src++;
	}

	if (braces)
	{
		if (*src != '}')
			goto syntax_error;
		src++;
	}

	if (*src != '\0')
		goto syntax_error;

	return;

syntax_error:
	ereport(ERROR,
			(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
			 errmsg("invalid input syntax for type %s: \"%s\"",
					"uuid", source)));
}

Datum
uuid_recv(PG_FUNCTION_ARGS)
{
	StringInfo	buffer = (StringInfo) PG_GETARG_POINTER(0);
	pg_uuid_t  *uuid;

	uuid = (pg_uuid_t *) palloc(UUID_LEN);
	memcpy(uuid->data, pq_getmsgbytes(buffer, UUID_LEN), UUID_LEN);
	PG_RETURN_POINTER(uuid);
}

Datum
uuid_send(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *uuid = PG_GETARG_UUID_P(0);
	StringInfoData buffer;

	pq_begintypsend(&buffer);
	pq_sendbytes(&buffer, (char *) uuid->data, UUID_LEN);
	PG_RETURN_BYTEA_P(pq_endtypsend(&buffer));
}

/* internal uuid compare function */
static int
uuid_internal_cmp(const pg_uuid_t *arg1, const pg_uuid_t *arg2)
{
	return memcmp(arg1->data, arg2->data, UUID_LEN);
}

Datum
uuid_lt(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_BOOL(uuid_internal_cmp(arg1, arg2) < 0);
}

Datum
uuid_le(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_BOOL(uuid_internal_cmp(arg1, arg2) <= 0);
}

Datum
uuid_eq(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_BOOL(uuid_internal_cmp(arg1, arg2) == 0);
}

Datum
uuid_ge(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_BOOL(uuid_internal_cmp(arg1, arg2) >= 0);
}

Datum
uuid_gt(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_BOOL(uuid_internal_cmp(arg1, arg2) > 0);
}

Datum
uuid_ne(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_BOOL(uuid_internal_cmp(arg1, arg2) != 0);
}

/* handler for btree index operator */
Datum
uuid_cmp(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *arg1 = PG_GETARG_UUID_P(0);
	pg_uuid_t  *arg2 = PG_GETARG_UUID_P(1);

	PG_RETURN_INT32(uuid_internal_cmp(arg1, arg2));
}

/*
 * Sort support strategy routine
 */
Datum
uuid_sortsupport(PG_FUNCTION_ARGS)
{
	SortSupport ssup = (SortSupport) PG_GETARG_POINTER(0);

	ssup->comparator = uuid_fast_cmp;
	ssup->ssup_extra = NULL;

	if (ssup->abbreviate)
	{
		uuid_sortsupport_state *uss;
		MemoryContext oldcontext;

		oldcontext = MemoryContextSwitchTo(ssup->ssup_cxt);

		uss = palloc(sizeof(uuid_sortsupport_state));
		uss->input_count = 0;
		uss->estimating = true;
		initHyperLogLog(&uss->abbr_card, 10);

		ssup->ssup_extra = uss;

		ssup->comparator = uuid_cmp_abbrev;
		ssup->abbrev_converter = uuid_abbrev_convert;
		ssup->abbrev_abort = uuid_abbrev_abort;
		ssup->abbrev_full_comparator = uuid_fast_cmp;

		MemoryContextSwitchTo(oldcontext);
	}

	PG_RETURN_VOID();
}

/*
 * SortSupport comparison func
 */
static int
uuid_fast_cmp(Datum x, Datum y, SortSupport ssup)
{
	pg_uuid_t  *arg1 = DatumGetUUIDP(x);
	pg_uuid_t  *arg2 = DatumGetUUIDP(y);

	return uuid_internal_cmp(arg1, arg2);
}

/*
 * Abbreviated key comparison func
 */
static int
uuid_cmp_abbrev(Datum x, Datum y, SortSupport ssup)
{
	if (x > y)
		return 1;
	else if (x == y)
		return 0;
	else
		return -1;
}

/*
 * Callback for estimating effectiveness of abbreviated key optimization.
 *
 * We pay no attention to the cardinality of the non-abbreviated data, because
 * there is no equality fast-path within authoritative uuid comparator.
 */
static bool
uuid_abbrev_abort(int memtupcount, SortSupport ssup)
{
	uuid_sortsupport_state *uss = ssup->ssup_extra;
	double		abbr_card;

	if (memtupcount < 10000 || uss->input_count < 10000 || !uss->estimating)
		return false;

	abbr_card = estimateHyperLogLog(&uss->abbr_card);

	/*
	 * If we have >100k distinct values, then even if we were sorting many
	 * billion rows we'd likely still break even, and the penalty of undoing
	 * that many rows of abbrevs would probably not be worth it.  Stop even
	 * counting at that point.
	 */
	if (abbr_card > 100000.0)
	{
#ifdef TRACE_SORT
		if (trace_sort)
			elog(LOG,
				 "uuid_abbrev: estimation ends at cardinality %f"
				 " after " INT64_FORMAT " values (%d rows)",
				 abbr_card, uss->input_count, memtupcount);
#endif
		uss->estimating = false;
		return false;
	}

	/*
	 * Target minimum cardinality is 1 per ~2k of non-null inputs.  0.5 row
	 * fudge factor allows us to abort earlier on genuinely pathological data
	 * where we've had exactly one abbreviated value in the first 2k
	 * (non-null) rows.
	 */
	if (abbr_card < uss->input_count / 2000.0 + 0.5)
	{
#ifdef TRACE_SORT
		if (trace_sort)
			elog(LOG,
				 "uuid_abbrev: aborting abbreviation at cardinality %f"
				 " below threshold %f after " INT64_FORMAT " values (%d rows)",
				 abbr_card, uss->input_count / 2000.0 + 0.5, uss->input_count,
				 memtupcount);
#endif
		return true;
	}

#ifdef TRACE_SORT
	if (trace_sort)
		elog(LOG,
			 "uuid_abbrev: cardinality %f after " INT64_FORMAT
			 " values (%d rows)", abbr_card, uss->input_count, memtupcount);
#endif

	return false;
}

/*
 * Conversion routine for sortsupport.  Converts original uuid representation
 * to abbreviated key representation.  Our encoding strategy is simple -- pack
 * the first `sizeof(Datum)` bytes of uuid data into a Datum (on little-endian
 * machines, the bytes are stored in reverse order), and treat it as an
 * unsigned integer.
 */
static Datum
uuid_abbrev_convert(Datum original, SortSupport ssup)
{
	uuid_sortsupport_state *uss = ssup->ssup_extra;
	pg_uuid_t  *authoritative = DatumGetUUIDP(original);
	Datum		res;

	memcpy(&res, authoritative->data, sizeof(Datum));
	uss->input_count += 1;

	if (uss->estimating)
	{
		uint32		tmp;

#if SIZEOF_DATUM == 8
		tmp = (uint32) res ^ (uint32) ((uint64) res >> 32);
#else							/* SIZEOF_DATUM != 8 */
		tmp = (uint32) res;
#endif

		addHyperLogLog(&uss->abbr_card, DatumGetUInt32(hash_uint32(tmp)));
	}

	/*
	 * Byteswap on little-endian machines.
	 *
	 * This is needed so that uuid_cmp_abbrev() (an unsigned integer 3-way
	 * comparator) works correctly on all platforms.  If we didn't do this,
	 * the comparator would have to call memcmp() with a pair of pointers to
	 * the first byte of each abbreviated key, which is slower.
	 */
	res = DatumBigEndianToNative(res);

	return res;
}

/* hash index support */
Datum
uuid_hash(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *key = PG_GETARG_UUID_P(0);

	return hash_any(key->data, UUID_LEN);
}

Datum
uuid_hash_extended(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *key = PG_GETARG_UUID_P(0);

	return hash_any_extended(key->data, UUID_LEN, PG_GETARG_INT64(1));
}

Datum
gen_random_uuid(PG_FUNCTION_ARGS)
{
	pg_uuid_t  *uuid = palloc(UUID_LEN);

	if (!pg_strong_random(uuid, UUID_LEN))
		ereport(ERROR,
				(errcode(ERRCODE_INTERNAL_ERROR),
				 errmsg("could not generate random values")));

	/*
	 * Set magic numbers for a "version 4" (pseudorandom) UUID, see
	 * http://tools.ietf.org/html/rfc4122#section-4.4
	 */
	uuid->data[6] = (uuid->data[6] & 0x0f) | 0x40;	/* time_hi_and_version */
	uuid->data[8] = (uuid->data[8] & 0x3f) | 0x80;	/* clock_seq_hi_and_reserved */

	PG_RETURN_UUID_P(uuid);
}