xid.c

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/*-------------------------------------------------------------------------
 *
 * xid.c
 *    POSTGRES transaction identifier and command identifier datatypes.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/xid.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <limits.h>
 
#include "access/multixact.h"
#include "access/transam.h"
#include "access/xact.h"
#include "common/hashfn.h"
#include "common/int.h"
#include "libpq/pqformat.h"
#include "utils/builtins.h"
#include "utils/xid8.h"
 
#define PG_GETARG_COMMANDID(n)      DatumGetCommandId(PG_GETARG_DATUM(n))
#define PG_RETURN_COMMANDID(x)      return CommandIdGetDatum(x)
 
 
Datum
xidin(PG_FUNCTION_ARGS)
{
    char       *str = PG_GETARG_CSTRING(0);
    TransactionId result;
 
    result = uint32in_subr(str, NULL, "xid", fcinfo->context);
    PG_RETURN_TRANSACTIONID(result);
}
 
Datum
xidout(PG_FUNCTION_ARGS)
{
    TransactionId transactionId = PG_GETARG_TRANSACTIONID(0);
    char       *result = (char *) palloc(16);
 
    snprintf(result, 16, "%u", transactionId);
    PG_RETURN_CSTRING(result);
}
 
/*
 *      xidrecv         - converts external binary format to xid
 */
Datum
xidrecv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
 
    PG_RETURN_TRANSACTIONID((TransactionId) pq_getmsgint(buf, sizeof(TransactionId)));
}
 
/*
 *      xidsend         - converts xid to binary format
 */
Datum
xidsend(PG_FUNCTION_ARGS)
{
    TransactionId arg1 = PG_GETARG_TRANSACTIONID(0);
    StringInfoData buf;
 
    pq_begintypsend(&buf);
    pq_sendint32(&buf, arg1);
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}
 
/*
 *      xideq           - are two xids equal?
 */
Datum
xideq(PG_FUNCTION_ARGS)
{
    TransactionId xid1 = PG_GETARG_TRANSACTIONID(0);
    TransactionId xid2 = PG_GETARG_TRANSACTIONID(1);
 
    PG_RETURN_BOOL(TransactionIdEquals(xid1, xid2));
}
 
/*
 *      xidneq          - are two xids different?
 */
Datum
xidneq(PG_FUNCTION_ARGS)
{
    TransactionId xid1 = PG_GETARG_TRANSACTIONID(0);
    TransactionId xid2 = PG_GETARG_TRANSACTIONID(1);
 
    PG_RETURN_BOOL(!TransactionIdEquals(xid1, xid2));
}
 
Datum
hashxid(PG_FUNCTION_ARGS)
{
    return hash_uint32(PG_GETARG_TRANSACTIONID(0));
}
 
Datum
hashxidextended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended(PG_GETARG_TRANSACTIONID(0), PG_GETARG_INT64(1));
}
 
/*
 *      xid_age         - compute age of an XID (relative to latest stable xid)
 */
Datum
xid_age(PG_FUNCTION_ARGS)
{
    TransactionId xid = PG_GETARG_TRANSACTIONID(0);
    TransactionId now = GetStableLatestTransactionId();
 
    /* Permanent XIDs are always infinitely old */
    if (!TransactionIdIsNormal(xid))
        PG_RETURN_INT32(INT_MAX);
 
    PG_RETURN_INT32((int32) (now - xid));
}
 
/*
 *      mxid_age            - compute age of a multi XID (relative to latest stable mxid)
 */
Datum
mxid_age(PG_FUNCTION_ARGS)
{
    TransactionId xid = PG_GETARG_TRANSACTIONID(0);
    MultiXactId now = ReadNextMultiXactId();
 
    if (!MultiXactIdIsValid(xid))
        PG_RETURN_INT32(INT_MAX);
 
    PG_RETURN_INT32((int32) (now - xid));
}
 
/*
 * xidComparator
 *      qsort comparison function for XIDs
 *
 * We can't use wraparound comparison for XIDs because that does not respect
 * the triangle inequality!  Any old sort order will do.
 */
int
xidComparator(const void *arg1, const void *arg2)
{
    TransactionId xid1 = *(const TransactionId *) arg1;
    TransactionId xid2 = *(const TransactionId *) arg2;
 
    return pg_cmp_u32(xid1, xid2);
}
 
/*
 * xidLogicalComparator
 *      qsort comparison function for XIDs
 *
 * This is used to compare only XIDs from the same epoch (e.g. for backends
 * running at the same time). So there must be only normal XIDs, so there's
 * no issue with triangle inequality.
 */
int
xidLogicalComparator(const void *arg1, const void *arg2)
{
    TransactionId xid1 = *(const TransactionId *) arg1;
    TransactionId xid2 = *(const TransactionId *) arg2;
 
    Assert(TransactionIdIsNormal(xid1));
    Assert(TransactionIdIsNormal(xid2));
 
    if (TransactionIdPrecedes(xid1, xid2))
        return -1;
 
    if (TransactionIdPrecedes(xid2, xid1))
        return 1;
 
    return 0;
}
 
Datum
xid8toxid(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid = PG_GETARG_FULLTRANSACTIONID(0);
 
    PG_RETURN_TRANSACTIONID(XidFromFullTransactionId(fxid));
}
 
Datum
xid8in(PG_FUNCTION_ARGS)
{
    char       *str = PG_GETARG_CSTRING(0);
    uint64      result;
 
    result = uint64in_subr(str, NULL, "xid8", fcinfo->context);
    PG_RETURN_FULLTRANSACTIONID(FullTransactionIdFromU64(result));
}
 
Datum
xid8out(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid = PG_GETARG_FULLTRANSACTIONID(0);
    char       *result = (char *) palloc(21);
 
    snprintf(result, 21, UINT64_FORMAT, U64FromFullTransactionId(fxid));
    PG_RETURN_CSTRING(result);
}
 
Datum
xid8recv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
    uint64      value;
 
    value = (uint64) pq_getmsgint64(buf);
    PG_RETURN_FULLTRANSACTIONID(FullTransactionIdFromU64(value));
}
 
Datum
xid8send(PG_FUNCTION_ARGS)
{
    FullTransactionId arg1 = PG_GETARG_FULLTRANSACTIONID(0);
    StringInfoData buf;
 
    pq_begintypsend(&buf);
    pq_sendint64(&buf, (uint64) U64FromFullTransactionId(arg1));
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}
 
Datum
xid8eq(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    PG_RETURN_BOOL(FullTransactionIdEquals(fxid1, fxid2));
}
 
Datum
xid8ne(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    PG_RETURN_BOOL(!FullTransactionIdEquals(fxid1, fxid2));
}
 
Datum
xid8lt(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    PG_RETURN_BOOL(FullTransactionIdPrecedes(fxid1, fxid2));
}
 
Datum
xid8gt(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    PG_RETURN_BOOL(FullTransactionIdFollows(fxid1, fxid2));
}
 
Datum
xid8le(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    PG_RETURN_BOOL(FullTransactionIdPrecedesOrEquals(fxid1, fxid2));
}
 
Datum
xid8ge(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    PG_RETURN_BOOL(FullTransactionIdFollowsOrEquals(fxid1, fxid2));
}
 
Datum
xid8cmp(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    if (FullTransactionIdFollows(fxid1, fxid2))
        PG_RETURN_INT32(1);
    else if (FullTransactionIdEquals(fxid1, fxid2))
        PG_RETURN_INT32(0);
    else
        PG_RETURN_INT32(-1);
}
 
Datum
hashxid8(PG_FUNCTION_ARGS)
{
    return hashint8(fcinfo);
}
 
Datum
hashxid8extended(PG_FUNCTION_ARGS)
{
    return hashint8extended(fcinfo);
}
 
Datum
xid8_larger(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    if (FullTransactionIdFollows(fxid1, fxid2))
        PG_RETURN_FULLTRANSACTIONID(fxid1);
    else
        PG_RETURN_FULLTRANSACTIONID(fxid2);
}
 
Datum
xid8_smaller(PG_FUNCTION_ARGS)
{
    FullTransactionId fxid1 = PG_GETARG_FULLTRANSACTIONID(0);
    FullTransactionId fxid2 = PG_GETARG_FULLTRANSACTIONID(1);
 
    if (FullTransactionIdPrecedes(fxid1, fxid2))
        PG_RETURN_FULLTRANSACTIONID(fxid1);
    else
        PG_RETURN_FULLTRANSACTIONID(fxid2);
}
 
/*****************************************************************************
 *   COMMAND IDENTIFIER ROUTINES                                             *
 *****************************************************************************/
 
/*
 *      cidin   - converts CommandId to internal representation.
 */
Datum
cidin(PG_FUNCTION_ARGS)
{
    char       *str = PG_GETARG_CSTRING(0);
    CommandId   result;
 
    result = uint32in_subr(str, NULL, "cid", fcinfo->context);
    PG_RETURN_COMMANDID(result);
}
 
/*
 *      cidout  - converts a cid to external representation.
 */
Datum
cidout(PG_FUNCTION_ARGS)
{
    CommandId   c = PG_GETARG_COMMANDID(0);
    char       *result = (char *) palloc(16);
 
    snprintf(result, 16, "%u", c);
    PG_RETURN_CSTRING(result);
}
 
/*
 *      cidrecv         - converts external binary format to cid
 */
Datum
cidrecv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
 
    PG_RETURN_COMMANDID((CommandId) pq_getmsgint(buf, sizeof(CommandId)));
}
 
/*
 *      cidsend         - converts cid to binary format
 */
Datum
cidsend(PG_FUNCTION_ARGS)
{
    CommandId   arg1 = PG_GETARG_COMMANDID(0);
    StringInfoData buf;
 
    pq_begintypsend(&buf);
    pq_sendint32(&buf, arg1);
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}
 
Datum
cideq(PG_FUNCTION_ARGS)
{
    CommandId   arg1 = PG_GETARG_COMMANDID(0);
    CommandId   arg2 = PG_GETARG_COMMANDID(1);
 
    PG_RETURN_BOOL(arg1 == arg2);
}
 
Datum
hashcid(PG_FUNCTION_ARGS)
{
    return hash_uint32(PG_GETARG_COMMANDID(0));
}
 
Datum
hashcidextended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended(PG_GETARG_COMMANDID(0), PG_GETARG_INT64(1));
}