pgstat_xact.c

Go to the documentation of this file.

/* -------------------------------------------------------------------------
 *
 * pgstat_xact.c
 *    Transactional integration for the cumulative statistics system.
 *
 * Copyright (c) 2001-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/activity/pgstat_xact.c
 * -------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/xact.h"
#include "pgstat.h"
#include "utils/memutils.h"
#include "utils/pgstat_internal.h"
 
 
typedef struct PgStat_PendingDroppedStatsItem
{
    xl_xact_stats_item item;
    bool        is_create;
    dlist_node  node;
} PgStat_PendingDroppedStatsItem;
 
 
static void AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit);
static void AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
                                            bool isCommit, int nestDepth);
 
static PgStat_SubXactStatus *pgStatXactStack = NULL;
 
 
/*
 * Called from access/transam/xact.c at top-level transaction commit/abort.
 */
void
AtEOXact_PgStat(bool isCommit, bool parallel)
{
    PgStat_SubXactStatus *xact_state;
 
    AtEOXact_PgStat_Database(isCommit, parallel);
 
    /* handle transactional stats information */
    xact_state = pgStatXactStack;
    if (xact_state != NULL)
    {
        Assert(xact_state->nest_level == 1);
        Assert(xact_state->prev == NULL);
 
        AtEOXact_PgStat_Relations(xact_state, isCommit);
        AtEOXact_PgStat_DroppedStats(xact_state, isCommit);
    }
    pgStatXactStack = NULL;
 
    /* Make sure any stats snapshot is thrown away */
    pgstat_clear_snapshot();
}
 
/*
 * When committing, drop stats for objects dropped in the transaction. When
 * aborting, drop stats for objects created in the transaction.
 */
static void
AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit)
{
    dlist_mutable_iter iter;
    int         not_freed_count = 0;
 
    if (dclist_count(&xact_state->pending_drops) == 0)
        return;
 
    dclist_foreach_modify(iter, &xact_state->pending_drops)
    {
        PgStat_PendingDroppedStatsItem *pending =
            dclist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
        xl_xact_stats_item *it = &pending->item;
        uint64      objid = ((uint64) it->objid_hi) << 32 | it->objid_lo;
 
        if (isCommit && !pending->is_create)
        {
            /*
             * Transaction that dropped an object committed. Drop the stats
             * too.
             */
            if (!pgstat_drop_entry(it->kind, it->dboid, objid))
                not_freed_count++;
        }
        else if (!isCommit && pending->is_create)
        {
            /*
             * Transaction that created an object aborted. Drop the stats
             * associated with the object.
             */
            if (!pgstat_drop_entry(it->kind, it->dboid, objid))
                not_freed_count++;
        }
 
        dclist_delete_from(&xact_state->pending_drops, &pending->node);
        pfree(pending);
    }
 
    if (not_freed_count > 0)
        pgstat_request_entry_refs_gc();
}
 
/*
 * Called from access/transam/xact.c at subtransaction commit/abort.
 */
void
AtEOSubXact_PgStat(bool isCommit, int nestDepth)
{
    PgStat_SubXactStatus *xact_state;
 
    /* merge the sub-transaction's transactional stats into the parent */
    xact_state = pgStatXactStack;
    if (xact_state != NULL &&
        xact_state->nest_level >= nestDepth)
    {
        /* delink xact_state from stack immediately to simplify reuse case */
        pgStatXactStack = xact_state->prev;
 
        AtEOSubXact_PgStat_Relations(xact_state, isCommit, nestDepth);
        AtEOSubXact_PgStat_DroppedStats(xact_state, isCommit, nestDepth);
 
        pfree(xact_state);
    }
}
 
/*
 * Like AtEOXact_PgStat_DroppedStats(), but for subtransactions.
 */
static void
AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
                                bool isCommit, int nestDepth)
{
    PgStat_SubXactStatus *parent_xact_state;
    dlist_mutable_iter iter;
    int         not_freed_count = 0;
 
    if (dclist_count(&xact_state->pending_drops) == 0)
        return;
 
    parent_xact_state = pgstat_get_xact_stack_level(nestDepth - 1);
 
    dclist_foreach_modify(iter, &xact_state->pending_drops)
    {
        PgStat_PendingDroppedStatsItem *pending =
            dclist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
        xl_xact_stats_item *it = &pending->item;
        uint64      objid = ((uint64) it->objid_hi) << 32 | it->objid_lo;
 
        dclist_delete_from(&xact_state->pending_drops, &pending->node);
 
        if (!isCommit && pending->is_create)
        {
            /*
             * Subtransaction creating a new stats object aborted. Drop the
             * stats object.
             */
            if (!pgstat_drop_entry(it->kind, it->dboid, objid))
                not_freed_count++;
            pfree(pending);
        }
        else if (isCommit)
        {
            /*
             * Subtransaction dropping a stats object committed. Can't yet
             * remove the stats object, the surrounding transaction might
             * still abort. Pass it on to the parent.
             */
            dclist_push_tail(&parent_xact_state->pending_drops, &pending->node);
        }
        else
        {
            pfree(pending);
        }
    }
 
    Assert(dclist_count(&xact_state->pending_drops) == 0);
    if (not_freed_count > 0)
        pgstat_request_entry_refs_gc();
}
 
/*
 * Save the transactional stats state at 2PC transaction prepare.
 */
void
AtPrepare_PgStat(void)
{
    PgStat_SubXactStatus *xact_state;
 
    xact_state = pgStatXactStack;
    if (xact_state != NULL)
    {
        Assert(xact_state->nest_level == 1);
        Assert(xact_state->prev == NULL);
 
        AtPrepare_PgStat_Relations(xact_state);
    }
}
 
/*
 * Clean up after successful PREPARE.
 *
 * Note: AtEOXact_PgStat is not called during PREPARE.
 */
void
PostPrepare_PgStat(void)
{
    PgStat_SubXactStatus *xact_state;
 
    /*
     * We don't bother to free any of the transactional state, since it's all
     * in TopTransactionContext and will go away anyway.
     */
    xact_state = pgStatXactStack;
    if (xact_state != NULL)
    {
        Assert(xact_state->nest_level == 1);
        Assert(xact_state->prev == NULL);
 
        PostPrepare_PgStat_Relations(xact_state);
    }
    pgStatXactStack = NULL;
 
    /* Make sure any stats snapshot is thrown away */
    pgstat_clear_snapshot();
}
 
/*
 * Ensure (sub)transaction stack entry for the given nest_level exists, adding
 * it if needed.
 */
PgStat_SubXactStatus *
pgstat_get_xact_stack_level(int nest_level)
{
    PgStat_SubXactStatus *xact_state;
 
    xact_state = pgStatXactStack;
    if (xact_state == NULL || xact_state->nest_level != nest_level)
    {
        xact_state = (PgStat_SubXactStatus *)
            MemoryContextAlloc(TopTransactionContext,
                               sizeof(PgStat_SubXactStatus));
        dclist_init(&xact_state->pending_drops);
        xact_state->nest_level = nest_level;
        xact_state->prev = pgStatXactStack;
        xact_state->first = NULL;
        pgStatXactStack = xact_state;
    }
    return xact_state;
}
 
/*
 * Get stat items that need to be dropped at commit / abort.
 *
 * When committing, stats for objects that have been dropped in the
 * transaction are returned. When aborting, stats for newly created objects are
 * returned.
 *
 * Used by COMMIT / ABORT and 2PC PREPARE processing when building their
 * respective WAL records, to ensure stats are dropped in case of a crash / on
 * standbys.
 *
 * The list of items is allocated in CurrentMemoryContext and must be freed by
 * the caller (directly or via memory context reset).
 */
int
pgstat_get_transactional_drops(bool isCommit, xl_xact_stats_item **items)
{
    PgStat_SubXactStatus *xact_state = pgStatXactStack;
    int         nitems = 0;
    dlist_iter  iter;
 
    if (xact_state == NULL)
        return 0;
 
    /*
     * We expect to be called for subtransaction abort (which logs a WAL
     * record), but not for subtransaction commit (which doesn't).
     */
    Assert(!isCommit || xact_state->nest_level == 1);
    Assert(!isCommit || xact_state->prev == NULL);
 
    *items = palloc(dclist_count(&xact_state->pending_drops)
                    * sizeof(xl_xact_stats_item));
 
    dclist_foreach(iter, &xact_state->pending_drops)
    {
        PgStat_PendingDroppedStatsItem *pending =
            dclist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
 
        if (isCommit && pending->is_create)
            continue;
        if (!isCommit && !pending->is_create)
            continue;
 
        Assert(nitems < dclist_count(&xact_state->pending_drops));
        (*items)[nitems++] = pending->item;
    }
 
    return nitems;
}
 
/*
 * Execute scheduled drops post-commit. Called from xact_redo_commit() /
 * xact_redo_abort() during recovery, and from FinishPreparedTransaction()
 * during normal 2PC COMMIT/ABORT PREPARED processing.
 */
void
pgstat_execute_transactional_drops(int ndrops, struct xl_xact_stats_item *items, bool is_redo)
{
    int         not_freed_count = 0;
 
    if (ndrops == 0)
        return;
 
    for (int i = 0; i < ndrops; i++)
    {
        xl_xact_stats_item *it = &items[i];
        uint64      objid = ((uint64) it->objid_hi) << 32 | it->objid_lo;
 
        if (!pgstat_drop_entry(it->kind, it->dboid, objid))
            not_freed_count++;
    }
 
    if (not_freed_count > 0)
        pgstat_request_entry_refs_gc();
}
 
static void
create_drop_transactional_internal(PgStat_Kind kind, Oid dboid, uint64 objid, bool is_create)
{
    int         nest_level = GetCurrentTransactionNestLevel();
    PgStat_SubXactStatus *xact_state;
    PgStat_PendingDroppedStatsItem *drop = (PgStat_PendingDroppedStatsItem *)
        MemoryContextAlloc(TopTransactionContext, sizeof(PgStat_PendingDroppedStatsItem));
 
    xact_state = pgstat_get_xact_stack_level(nest_level);
 
    drop->is_create = is_create;
    drop->item.kind = kind;
    drop->item.dboid = dboid;
    drop->item.objid_lo = (uint32) objid;
    drop->item.objid_hi = (uint32) (objid >> 32);
 
    dclist_push_tail(&xact_state->pending_drops, &drop->node);
}
 
/*
 * Create a stats entry for a newly created database object in a transactional
 * manner.
 *
 * I.e. if the current (sub-)transaction aborts, the stats entry will also be
 * dropped.
 */
void
pgstat_create_transactional(PgStat_Kind kind, Oid dboid, uint64 objid)
{
    if (pgstat_get_entry_ref(kind, dboid, objid, false, NULL))
    {
        ereport(WARNING,
                errmsg("resetting existing statistics for kind %s, db=%u, oid=%" PRIu64,
                       (pgstat_get_kind_info(kind))->name, dboid,
                       objid));
 
        pgstat_reset(kind, dboid, objid);
    }
 
    create_drop_transactional_internal(kind, dboid, objid, /* create */ true);
}
 
/*
 * Drop a stats entry for a just dropped database object in a transactional
 * manner.
 *
 * I.e. if the current (sub-)transaction aborts, the stats entry will stay
 * alive.
 */
void
pgstat_drop_transactional(PgStat_Kind kind, Oid dboid, uint64 objid)
{
    create_drop_transactional_internal(kind, dboid, objid, /* create */ false);
}