uuid.c

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/*-------------------------------------------------------------------------
 *
 * uuid.c
 *    Functions for the built-in type "uuid".
 *
 * Copyright (c) 2007-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/uuid.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <time.h>               /* for clock_gettime() */
 
#include "common/hashfn.h"
#include "lib/hyperloglog.h"
#include "libpq/pqformat.h"
#include "port/pg_bswap.h"
#include "utils/fmgrprotos.h"
#include "utils/guc.h"
#include "utils/sortsupport.h"
#include "utils/timestamp.h"
#include "utils/uuid.h"
 
/* helper macros */
#define NS_PER_S    INT64CONST(1000000000)
#define NS_PER_MS   INT64CONST(1000000)
#define NS_PER_US   INT64CONST(1000)
 
/*
 * UUID version 7 uses 12 bits in "rand_a" to store  1/4096 (or 2^12) fractions of
 * sub-millisecond. While most Unix-like platforms provide nanosecond-precision
 * timestamps, some systems only offer microsecond precision, limiting us to 10
 * bits of sub-millisecond information. For example, on macOS, real time is
 * truncated to microseconds. Additionally, MSVC uses the ported version of
 * gettimeofday() that returns microsecond precision.
 *
 * On systems with only 10 bits of sub-millisecond precision, we still use
 * 1/4096 parts of a millisecond, but fill lower 2 bits with random numbers
 * (see generate_uuidv7() for details).
 *
 * SUBMS_MINIMAL_STEP_NS defines the minimum number of nanoseconds that guarantees
 * an increase in the UUID's clock precision.
 */
#if defined(__darwin__) || defined(_MSC_VER)
#define SUBMS_MINIMAL_STEP_BITS 10
#else
#define SUBMS_MINIMAL_STEP_BITS 12
#endif
#define SUBMS_BITS  12
#define SUBMS_MINIMAL_STEP_NS ((NS_PER_MS / (1 << SUBMS_MINIMAL_STEP_BITS)) + 1)
 
/* 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, Node *escontext);
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 bool uuid_abbrev_abort(int memtupcount, SortSupport ssup);
static Datum uuid_abbrev_convert(Datum original, SortSupport ssup);
static inline void uuid_set_version(pg_uuid_t *uuid, unsigned char version);
static inline int64 get_real_time_ns_ascending();
 
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, fcinfo->context);
    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";
    char       *buf,
               *p;
    int         i;
 
    /* counts for the four hyphens and the zero-terminator */
    buf = palloc(2 * UUID_LEN + 5);
    p = 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)
            *p++ = '-';
 
        hi = uuid->data[i] >> 4;
        lo = uuid->data[i] & 0x0F;
 
        *p++ = hex_chars[hi];
        *p++ = hex_chars[lo];
    }
    *p = '\0';
 
    PG_RETURN_CSTRING(buf);
}
 
/*
 * 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, Node *escontext)
{
    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:
    ereturn(escontext,,
            (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, 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 = ssup_datum_unsigned_cmp;
        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);
}
 
/*
 * 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)
    {
        if (trace_sort)
            elog(LOG,
                 "uuid_abbrev: estimation ends at cardinality %f"
                 " after " INT64_FORMAT " values (%d rows)",
                 abbr_card, uss->input_count, memtupcount);
        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)
    {
        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);
        return true;
    }
 
    if (trace_sort)
        elog(LOG,
             "uuid_abbrev: cardinality %f after " INT64_FORMAT
             " values (%d rows)", abbr_card, uss->input_count, memtupcount);
 
    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 ssup_datum_unsigned_cmp() (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));
}
 
/*
 * Set the given UUID version and the variant bits
 */
static inline void
uuid_set_version(pg_uuid_t *uuid, unsigned char version)
{
    /* set version field, top four bits */
    uuid->data[6] = (uuid->data[6] & 0x0f) | (version << 4);
 
    /* set variant field, top two bits are 1, 0 */
    uuid->data[8] = (uuid->data[8] & 0x3f) | 0x80;
}
 
/*
 * Generate UUID version 4.
 *
 * All UUID bytes are filled with strong random numbers except version and
 * variant bits.
 */
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 and variant,
     * see https://datatracker.ietf.org/doc/html/rfc9562#name-uuid-version-4
     */
    uuid_set_version(uuid, 4);
 
    PG_RETURN_UUID_P(uuid);
}
 
/*
 * Get the current timestamp with nanosecond precision for UUID generation.
 * The returned timestamp is ensured to be at least SUBMS_MINIMAL_STEP greater
 * than the previous returned timestamp (on this backend).
 */
static inline int64
get_real_time_ns_ascending()
{
    static int64 previous_ns = 0;
    int64       ns;
 
    /* Get the current real timestamp */
 
#ifdef  _MSC_VER
    struct timeval tmp;
 
    gettimeofday(&tmp, NULL);
    ns = tmp.tv_sec * NS_PER_S + tmp.tv_usec * NS_PER_US;
#else
    struct timespec tmp;
 
    /*
     * We don't use gettimeofday(), instead use clock_gettime() with
     * CLOCK_REALTIME where available in order to get a high-precision
     * (nanoseconds) real timestamp.
     *
     * Note while a timestamp returned by clock_gettime() with CLOCK_REALTIME
     * is nanosecond-precision on most Unix-like platforms, on some platforms
     * such as macOS it's restricted to microsecond-precision.
     */
    clock_gettime(CLOCK_REALTIME, &tmp);
    ns = tmp.tv_sec * NS_PER_S + tmp.tv_nsec;
#endif
 
    /* Guarantee the minimal step advancement of the timestamp */
    if (previous_ns + SUBMS_MINIMAL_STEP_NS >= ns)
        ns = previous_ns + SUBMS_MINIMAL_STEP_NS;
    previous_ns = ns;
 
    return ns;
}
 
/*
 * Generate UUID version 7 per RFC 9562, with the given timestamp.
 *
 * UUID version 7 consists of a Unix timestamp in milliseconds (48 bits) and
 * 74 random bits, excluding the required version and variant bits. To ensure
 * monotonicity in scenarios of high-frequency UUID generation, we employ the
 * method "Replace Leftmost Random Bits with Increased Clock Precision (Method 3)",
 * described in the RFC. This method utilizes 12 bits from the "rand_a" bits
 * to store a 1/4096 (or 2^12) fraction of sub-millisecond precision.
 *
 * ns is a number of nanoseconds since start of the UNIX epoch. This value is
 * used for time-dependent bits of UUID.
 */
static pg_uuid_t *
generate_uuidv7(int64 ns)
{
    pg_uuid_t  *uuid = palloc(UUID_LEN);
    int64       unix_ts_ms;
    int32       increased_clock_precision;
 
    unix_ts_ms = ns / NS_PER_MS;
 
    /* Fill in time part */
    uuid->data[0] = (unsigned char) (unix_ts_ms >> 40);
    uuid->data[1] = (unsigned char) (unix_ts_ms >> 32);
    uuid->data[2] = (unsigned char) (unix_ts_ms >> 24);
    uuid->data[3] = (unsigned char) (unix_ts_ms >> 16);
    uuid->data[4] = (unsigned char) (unix_ts_ms >> 8);
    uuid->data[5] = (unsigned char) unix_ts_ms;
 
    /*
     * sub-millisecond timestamp fraction (SUBMS_BITS bits, not
     * SUBMS_MINIMAL_STEP_BITS)
     */
    increased_clock_precision = ((ns % NS_PER_MS) * (1 << SUBMS_BITS)) / NS_PER_MS;
 
    /* Fill the increased clock precision to "rand_a" bits */
    uuid->data[6] = (unsigned char) (increased_clock_precision >> 8);
    uuid->data[7] = (unsigned char) (increased_clock_precision);
 
    /* fill everything after the increased clock precision with random bytes */
    if (!pg_strong_random(&uuid->data[8], UUID_LEN - 8))
        ereport(ERROR,
                (errcode(ERRCODE_INTERNAL_ERROR),
                 errmsg("could not generate random values")));
 
#if SUBMS_MINIMAL_STEP_BITS == 10
 
    /*
     * On systems that have only 10 bits of sub-ms precision,  2 least
     * significant are dependent on other time-specific bits, and they do not
     * contribute to uniqueness. To make these bit random we mix in two bits
     * from CSPRNG. SUBMS_MINIMAL_STEP is chosen so that we still guarantee
     * monotonicity despite altering these bits.
     */
    uuid->data[7] = uuid->data[7] ^ (uuid->data[8] >> 6);
#endif
 
    /*
     * Set magic numbers for a "version 7" (pseudorandom) UUID and variant,
     * see https://www.rfc-editor.org/rfc/rfc9562#name-version-field
     */
    uuid_set_version(uuid, 7);
 
    return uuid;
}
 
/*
 * Generate UUID version 7 with the current timestamp.
 */
Datum
uuidv7(PG_FUNCTION_ARGS)
{
    pg_uuid_t  *uuid = generate_uuidv7(get_real_time_ns_ascending());
 
    PG_RETURN_UUID_P(uuid);
}
 
/*
 * Similar to uuidv7() but with the timestamp adjusted by the given interval.
 */
Datum
uuidv7_interval(PG_FUNCTION_ARGS)
{
    Interval   *shift = PG_GETARG_INTERVAL_P(0);
    TimestampTz ts;
    pg_uuid_t  *uuid;
    int64       ns = get_real_time_ns_ascending();
 
    /*
     * Shift the current timestamp by the given interval. To calculate time
     * shift correctly, we convert the UNIX epoch to TimestampTz and use
     * timestamptz_pl_interval(). Since this calculation is done with
     * microsecond precision, we carry nanoseconds from original ns value to
     * shifted ns value.
     */
 
    ts = (TimestampTz) (ns / NS_PER_US) -
        (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY * USECS_PER_SEC;
 
    /* Compute time shift */
    ts = DatumGetTimestampTz(DirectFunctionCall2(timestamptz_pl_interval,
                                                 TimestampTzGetDatum(ts),
                                                 IntervalPGetDatum(shift)));
 
    /*
     * Convert a TimestampTz value back to an UNIX epoch and back nanoseconds.
     */
    ns = (ts + (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY * USECS_PER_SEC)
        * NS_PER_US + ns % NS_PER_US;
 
    /* Generate an UUIDv7 */
    uuid = generate_uuidv7(ns);
 
    PG_RETURN_UUID_P(uuid);
}
 
/*
 * Start of a Gregorian epoch == date2j(1582,10,15)
 * We cast it to 64-bit because it's used in overflow-prone computations
 */
#define GREGORIAN_EPOCH_JDATE  INT64CONST(2299161)
 
/*
 * Extract timestamp from UUID.
 *
 * Returns null if not RFC 9562 variant or not a version that has a timestamp.
 */
Datum
uuid_extract_timestamp(PG_FUNCTION_ARGS)
{
    pg_uuid_t  *uuid = PG_GETARG_UUID_P(0);
    int         version;
    uint64      tms;
    TimestampTz ts;
 
    /* check if RFC 9562 variant */
    if ((uuid->data[8] & 0xc0) != 0x80)
        PG_RETURN_NULL();
 
    version = uuid->data[6] >> 4;
 
    if (version == 1)
    {
        tms = ((uint64) uuid->data[0] << 24)
            + ((uint64) uuid->data[1] << 16)
            + ((uint64) uuid->data[2] << 8)
            + ((uint64) uuid->data[3])
            + ((uint64) uuid->data[4] << 40)
            + ((uint64) uuid->data[5] << 32)
            + (((uint64) uuid->data[6] & 0xf) << 56)
            + ((uint64) uuid->data[7] << 48);
 
        /* convert 100-ns intervals to us, then adjust */
        ts = (TimestampTz) (tms / 10) -
            ((uint64) POSTGRES_EPOCH_JDATE - GREGORIAN_EPOCH_JDATE) * SECS_PER_DAY * USECS_PER_SEC;
        PG_RETURN_TIMESTAMPTZ(ts);
    }
 
    if (version == 7)
    {
        tms = (uuid->data[5])
            + (((uint64) uuid->data[4]) << 8)
            + (((uint64) uuid->data[3]) << 16)
            + (((uint64) uuid->data[2]) << 24)
            + (((uint64) uuid->data[1]) << 32)
            + (((uint64) uuid->data[0]) << 40);
 
        /* convert ms to us, then adjust */
        ts = (TimestampTz) (tms * NS_PER_US) -
            (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY * USECS_PER_SEC;
 
        PG_RETURN_TIMESTAMPTZ(ts);
    }
 
    /* not a timestamp-containing UUID version */
    PG_RETURN_NULL();
}
 
/*
 * Extract UUID version.
 *
 * Returns null if not RFC 9562 variant.
 */
Datum
uuid_extract_version(PG_FUNCTION_ARGS)
{
    pg_uuid_t  *uuid = PG_GETARG_UUID_P(0);
    uint16      version;
 
    /* check if RFC 9562 variant */
    if ((uuid->data[8] & 0xc0) != 0x80)
        PG_RETURN_NULL();
 
    version = uuid->data[6] >> 4;
 
    PG_RETURN_UINT16(version);
}