multixactfuncs.c

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/*-------------------------------------------------------------------------
 *
 * multixactfuncs.c
 *    Functions for accessing multixact-related data.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/multixactfuncs.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/multixact.h"
#include "access/multixact_internal.h"
#include "catalog/pg_authid_d.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "utils/acl.h"
#include "utils/builtins.h"
 
/*
 * pg_get_multixact_members
 *
 * Returns information about the MultiXactMembers of the specified
 * MultiXactId.
 */
Datum
pg_get_multixact_members(PG_FUNCTION_ARGS)
{
    typedef struct
    {
        MultiXactMember *members;
        int         nmembers;
        int         iter;
    } mxact;
    MultiXactId mxid = PG_GETARG_TRANSACTIONID(0);
    mxact      *multi;
    FuncCallContext *funccxt;
 
    if (mxid < FirstMultiXactId)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid MultiXactId: %u", mxid)));
 
    if (SRF_IS_FIRSTCALL())
    {
        MemoryContext oldcxt;
        TupleDesc   tupdesc;
 
        funccxt = SRF_FIRSTCALL_INIT();
        oldcxt = MemoryContextSwitchTo(funccxt->multi_call_memory_ctx);
 
        multi = palloc_object(mxact);
        /* no need to allow for old values here */
        multi->nmembers = GetMultiXactIdMembers(mxid, &multi->members, false,
                                                false);
        multi->iter = 0;
 
        if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
            elog(ERROR, "return type must be a row type");
        funccxt->tuple_desc = tupdesc;
        funccxt->attinmeta = TupleDescGetAttInMetadata(tupdesc);
        funccxt->user_fctx = multi;
 
        MemoryContextSwitchTo(oldcxt);
    }
 
    funccxt = SRF_PERCALL_SETUP();
    multi = (mxact *) funccxt->user_fctx;
 
    while (multi->iter < multi->nmembers)
    {
        HeapTuple   tuple;
        char       *values[2];
 
        values[0] = psprintf("%u", multi->members[multi->iter].xid);
        values[1] = mxstatus_to_string(multi->members[multi->iter].status);
 
        tuple = BuildTupleFromCStrings(funccxt->attinmeta, values);
 
        multi->iter++;
        pfree(values[0]);
        SRF_RETURN_NEXT(funccxt, HeapTupleGetDatum(tuple));
    }
 
    SRF_RETURN_DONE(funccxt);
}
 
/*
 * pg_get_multixact_stats
 *
 * Returns statistics about current multixact usage.
 */
Datum
pg_get_multixact_stats(PG_FUNCTION_ARGS)
{
    TupleDesc   tupdesc;
    Datum       values[4];
    bool        nulls[4];
    uint64      members;
    MultiXactId oldestMultiXactId;
    uint32      multixacts;
    MultiXactOffset oldestOffset;
    MultiXactOffset nextOffset;
    uint64      membersBytes;
 
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("return type must be a row type")));
 
    GetMultiXactInfo(&multixacts, &nextOffset, &oldestMultiXactId, &oldestOffset);
    members = nextOffset - oldestOffset;
 
    membersBytes = MultiXactOffsetStorageSize(nextOffset, oldestOffset);
 
    if (!has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
    {
        /*
         * Only superusers and roles with privileges of pg_read_all_stats can
         * see details.
         */
        memset(nulls, true, sizeof(bool) * tupdesc->natts);
    }
    else
    {
        values[0] = UInt32GetDatum(multixacts);
        values[1] = Int64GetDatum(members);
        values[2] = Int64GetDatum(membersBytes);
        values[3] = UInt32GetDatum(oldestMultiXactId);
        memset(nulls, false, sizeof(nulls));
    }
 
    return HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls));
}