/*-------------------------------------------------------------------------

 *

 * 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 "access/xlog.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];

  if (RecoveryInProgress())

    ereport(ERROR,

        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),

         errmsg("recovery is in progress"),

         errhint("%s cannot be executed during recovery.",

             "pg_get_multixact_stats()")));

  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")));

  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

  {

    uint64    members;

    MultiXactId oldestMultiXactId;

    uint32    multixacts;

    MultiXactOffset oldestOffset;

    MultiXactOffset nextOffset;

    uint64    membersBytes;

    GetMultiXactInfo(&multixacts, &nextOffset, &oldestMultiXactId, &oldestOffset);

    members = nextOffset - oldestOffset;

    membersBytes = MultiXactOffsetStorageSize(nextOffset, oldestOffset);

    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));

}