pgstat_relation.c

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/* -------------------------------------------------------------------------
 *
 * pgstat_relation.c
 *    Implementation of relation statistics.
 *
 * This file contains the implementation of function relation. It is kept
 * separate from pgstat.c to enforce the line between the statistics access /
 * storage implementation and the details about individual types of
 * statistics.
 *
 * Copyright (c) 2001-2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/activity/pgstat_relation.c
 * -------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/twophase_rmgr.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "postmaster/autovacuum.h"
#include "utils/memutils.h"
#include "utils/pgstat_internal.h"
#include "utils/rel.h"
#include "utils/timestamp.h"
 
 
/* Record that's written to 2PC state file when pgstat state is persisted */
typedef struct TwoPhasePgStatRecord
{
    PgStat_Counter tuples_inserted; /* tuples inserted in xact */
    PgStat_Counter tuples_updated;  /* tuples updated in xact */
    PgStat_Counter tuples_deleted;  /* tuples deleted in xact */
    /* tuples i/u/d prior to truncate/drop */
    PgStat_Counter inserted_pre_truncdrop;
    PgStat_Counter updated_pre_truncdrop;
    PgStat_Counter deleted_pre_truncdrop;
    Oid         id;             /* table's OID */
    bool        shared;         /* is it a shared catalog? */
    bool        truncdropped;   /* was the relation truncated/dropped? */
} TwoPhasePgStatRecord;
 
 
static PgStat_TableStatus *pgstat_prep_relation_pending(Oid rel_id, bool isshared);
static void add_tabstat_xact_level(PgStat_TableStatus *pgstat_info, int nest_level);
static void ensure_tabstat_xact_level(PgStat_TableStatus *pgstat_info);
static void save_truncdrop_counters(PgStat_TableXactStatus *trans, bool is_drop);
static void restore_truncdrop_counters(PgStat_TableXactStatus *trans);
 
 
/*
 * Copy stats between relations. This is used for things like REINDEX
 * CONCURRENTLY.
 */
void
pgstat_copy_relation_stats(Relation dst, Relation src)
{
    PgStat_StatTabEntry *srcstats;
    PgStatShared_Relation *dstshstats;
    PgStat_EntryRef *dst_ref;
 
    srcstats = pgstat_fetch_stat_tabentry_ext(src->rd_rel->relisshared,
                                              RelationGetRelid(src));
    if (!srcstats)
        return;
 
    dst_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_RELATION,
                                          dst->rd_rel->relisshared ? InvalidOid : MyDatabaseId,
                                          RelationGetRelid(dst),
                                          false);
 
    dstshstats = (PgStatShared_Relation *) dst_ref->shared_stats;
    dstshstats->stats = *srcstats;
 
    pgstat_unlock_entry(dst_ref);
}
 
/*
 * Initialize a relcache entry to count access statistics.  Called whenever a
 * relation is opened.
 *
 * We assume that a relcache entry's pgstat_info field is zeroed by relcache.c
 * when the relcache entry is made; thereafter it is long-lived data.
 *
 * This does not create a reference to a stats entry in shared memory, nor
 * allocate memory for the pending stats. That happens in
 * pgstat_assoc_relation().
 */
void
pgstat_init_relation(Relation rel)
{
    char        relkind = rel->rd_rel->relkind;
 
    /*
     * We only count stats for relations with storage and partitioned tables
     */
    if (!RELKIND_HAS_STORAGE(relkind) && relkind != RELKIND_PARTITIONED_TABLE)
    {
        rel->pgstat_enabled = false;
        rel->pgstat_info = NULL;
        return;
    }
 
    if (!pgstat_track_counts)
    {
        if (rel->pgstat_info)
            pgstat_unlink_relation(rel);
 
        /* We're not counting at all */
        rel->pgstat_enabled = false;
        rel->pgstat_info = NULL;
        return;
    }
 
    rel->pgstat_enabled = true;
}
 
/*
 * Prepare for statistics for this relation to be collected.
 *
 * This ensures we have a reference to the stats entry before stats can be
 * generated. That is important because a relation drop in another connection
 * could otherwise lead to the stats entry being dropped, which then later
 * would get recreated when flushing stats.
 *
 * This is separate from pgstat_init_relation() as it is not uncommon for
 * relcache entries to be opened without ever getting stats reported.
 */
void
pgstat_assoc_relation(Relation rel)
{
    Assert(rel->pgstat_enabled);
    Assert(rel->pgstat_info == NULL);
 
    /* Else find or make the PgStat_TableStatus entry, and update link */
    rel->pgstat_info = pgstat_prep_relation_pending(RelationGetRelid(rel),
                                                    rel->rd_rel->relisshared);
 
    /* don't allow link a stats to multiple relcache entries */
    Assert(rel->pgstat_info->relation == NULL);
 
    /* mark this relation as the owner */
    rel->pgstat_info->relation = rel;
}
 
/*
 * Break the mutual link between a relcache entry and pending stats entry.
 * This must be called whenever one end of the link is removed.
 */
void
pgstat_unlink_relation(Relation rel)
{
    /* remove the link to stats info if any */
    if (rel->pgstat_info == NULL)
        return;
 
    /* link sanity check */
    Assert(rel->pgstat_info->relation == rel);
    rel->pgstat_info->relation = NULL;
    rel->pgstat_info = NULL;
}
 
/*
 * Ensure that stats are dropped if transaction aborts.
 */
void
pgstat_create_relation(Relation rel)
{
    pgstat_create_transactional(PGSTAT_KIND_RELATION,
                                rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId,
                                RelationGetRelid(rel));
}
 
/*
 * Ensure that stats are dropped if transaction commits.
 */
void
pgstat_drop_relation(Relation rel)
{
    int         nest_level = GetCurrentTransactionNestLevel();
    PgStat_TableStatus *pgstat_info;
 
    pgstat_drop_transactional(PGSTAT_KIND_RELATION,
                              rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId,
                              RelationGetRelid(rel));
 
    if (!pgstat_should_count_relation(rel))
        return;
 
    /*
     * Transactionally set counters to 0. That ensures that accesses to
     * pg_stat_xact_all_tables inside the transaction show 0.
     */
    pgstat_info = rel->pgstat_info;
    if (pgstat_info->trans &&
        pgstat_info->trans->nest_level == nest_level)
    {
        save_truncdrop_counters(pgstat_info->trans, true);
        pgstat_info->trans->tuples_inserted = 0;
        pgstat_info->trans->tuples_updated = 0;
        pgstat_info->trans->tuples_deleted = 0;
    }
}
 
/*
 * Report that the table was just vacuumed and flush IO statistics.
 */
void
pgstat_report_vacuum(Oid tableoid, bool shared,
                     PgStat_Counter livetuples, PgStat_Counter deadtuples)
{
    PgStat_EntryRef *entry_ref;
    PgStatShared_Relation *shtabentry;
    PgStat_StatTabEntry *tabentry;
    Oid         dboid = (shared ? InvalidOid : MyDatabaseId);
    TimestampTz ts;
 
    if (!pgstat_track_counts)
        return;
 
    /* Store the data in the table's hash table entry. */
    ts = GetCurrentTimestamp();
 
    /* block acquiring lock for the same reason as pgstat_report_autovac() */
    entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_RELATION,
                                            dboid, tableoid, false);
 
    shtabentry = (PgStatShared_Relation *) entry_ref->shared_stats;
    tabentry = &shtabentry->stats;
 
    tabentry->live_tuples = livetuples;
    tabentry->dead_tuples = deadtuples;
 
    /*
     * It is quite possible that a non-aggressive VACUUM ended up skipping
     * various pages, however, we'll zero the insert counter here regardless.
     * It's currently used only to track when we need to perform an "insert"
     * autovacuum, which are mainly intended to freeze newly inserted tuples.
     * Zeroing this may just mean we'll not try to vacuum the table again
     * until enough tuples have been inserted to trigger another insert
     * autovacuum.  An anti-wraparound autovacuum will catch any persistent
     * stragglers.
     */
    tabentry->ins_since_vacuum = 0;
 
    if (AmAutoVacuumWorkerProcess())
    {
        tabentry->last_autovacuum_time = ts;
        tabentry->autovacuum_count++;
    }
    else
    {
        tabentry->last_vacuum_time = ts;
        tabentry->vacuum_count++;
    }
 
    pgstat_unlock_entry(entry_ref);
 
    /*
     * Flush IO statistics now. pgstat_report_stat() will flush IO stats,
     * however this will not be called until after an entire autovacuum cycle
     * is done -- which will likely vacuum many relations -- or until the
     * VACUUM command has processed all tables and committed.
     */
    pgstat_flush_io(false);
}
 
/*
 * Report that the table was just analyzed and flush IO statistics.
 *
 * Caller must provide new live- and dead-tuples estimates, as well as a
 * flag indicating whether to reset the mod_since_analyze counter.
 */
void
pgstat_report_analyze(Relation rel,
                      PgStat_Counter livetuples, PgStat_Counter deadtuples,
                      bool resetcounter)
{
    PgStat_EntryRef *entry_ref;
    PgStatShared_Relation *shtabentry;
    PgStat_StatTabEntry *tabentry;
    Oid         dboid = (rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId);
 
    if (!pgstat_track_counts)
        return;
 
    /*
     * Unlike VACUUM, ANALYZE might be running inside a transaction that has
     * already inserted and/or deleted rows in the target table. ANALYZE will
     * have counted such rows as live or dead respectively. Because we will
     * report our counts of such rows at transaction end, we should subtract
     * off these counts from the update we're making now, else they'll be
     * double-counted after commit.  (This approach also ensures that the
     * shared stats entry ends up with the right numbers if we abort instead
     * of committing.)
     *
     * Waste no time on partitioned tables, though.
     */
    if (pgstat_should_count_relation(rel) &&
        rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
    {
        PgStat_TableXactStatus *trans;
 
        for (trans = rel->pgstat_info->trans; trans; trans = trans->upper)
        {
            livetuples -= trans->tuples_inserted - trans->tuples_deleted;
            deadtuples -= trans->tuples_updated + trans->tuples_deleted;
        }
        /* count stuff inserted by already-aborted subxacts, too */
        deadtuples -= rel->pgstat_info->counts.delta_dead_tuples;
        /* Since ANALYZE's counts are estimates, we could have underflowed */
        livetuples = Max(livetuples, 0);
        deadtuples = Max(deadtuples, 0);
    }
 
    /* block acquiring lock for the same reason as pgstat_report_autovac() */
    entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_RELATION, dboid,
                                            RelationGetRelid(rel),
                                            false);
    /* can't get dropped while accessed */
    Assert(entry_ref != NULL && entry_ref->shared_stats != NULL);
 
    shtabentry = (PgStatShared_Relation *) entry_ref->shared_stats;
    tabentry = &shtabentry->stats;
 
    tabentry->live_tuples = livetuples;
    tabentry->dead_tuples = deadtuples;
 
    /*
     * If commanded, reset mod_since_analyze to zero.  This forgets any
     * changes that were committed while the ANALYZE was in progress, but we
     * have no good way to estimate how many of those there were.
     */
    if (resetcounter)
        tabentry->mod_since_analyze = 0;
 
    if (AmAutoVacuumWorkerProcess())
    {
        tabentry->last_autoanalyze_time = GetCurrentTimestamp();
        tabentry->autoanalyze_count++;
    }
    else
    {
        tabentry->last_analyze_time = GetCurrentTimestamp();
        tabentry->analyze_count++;
    }
 
    pgstat_unlock_entry(entry_ref);
 
    /* see pgstat_report_vacuum() */
    pgstat_flush_io(false);
}
 
/*
 * count a tuple insertion of n tuples
 */
void
pgstat_count_heap_insert(Relation rel, PgStat_Counter n)
{
    if (pgstat_should_count_relation(rel))
    {
        PgStat_TableStatus *pgstat_info = rel->pgstat_info;
 
        ensure_tabstat_xact_level(pgstat_info);
        pgstat_info->trans->tuples_inserted += n;
    }
}
 
/*
 * count a tuple update
 */
void
pgstat_count_heap_update(Relation rel, bool hot, bool newpage)
{
    Assert(!(hot && newpage));
 
    if (pgstat_should_count_relation(rel))
    {
        PgStat_TableStatus *pgstat_info = rel->pgstat_info;
 
        ensure_tabstat_xact_level(pgstat_info);
        pgstat_info->trans->tuples_updated++;
 
        /*
         * tuples_hot_updated and tuples_newpage_updated counters are
         * nontransactional, so just advance them
         */
        if (hot)
            pgstat_info->counts.tuples_hot_updated++;
        else if (newpage)
            pgstat_info->counts.tuples_newpage_updated++;
    }
}
 
/*
 * count a tuple deletion
 */
void
pgstat_count_heap_delete(Relation rel)
{
    if (pgstat_should_count_relation(rel))
    {
        PgStat_TableStatus *pgstat_info = rel->pgstat_info;
 
        ensure_tabstat_xact_level(pgstat_info);
        pgstat_info->trans->tuples_deleted++;
    }
}
 
/*
 * update tuple counters due to truncate
 */
void
pgstat_count_truncate(Relation rel)
{
    if (pgstat_should_count_relation(rel))
    {
        PgStat_TableStatus *pgstat_info = rel->pgstat_info;
 
        ensure_tabstat_xact_level(pgstat_info);
        save_truncdrop_counters(pgstat_info->trans, false);
        pgstat_info->trans->tuples_inserted = 0;
        pgstat_info->trans->tuples_updated = 0;
        pgstat_info->trans->tuples_deleted = 0;
    }
}
 
/*
 * update dead-tuples count
 *
 * The semantics of this are that we are reporting the nontransactional
 * recovery of "delta" dead tuples; so delta_dead_tuples decreases
 * rather than increasing, and the change goes straight into the per-table
 * counter, not into transactional state.
 */
void
pgstat_update_heap_dead_tuples(Relation rel, int delta)
{
    if (pgstat_should_count_relation(rel))
    {
        PgStat_TableStatus *pgstat_info = rel->pgstat_info;
 
        pgstat_info->counts.delta_dead_tuples -= delta;
    }
}
 
/*
 * Support function for the SQL-callable pgstat* functions. Returns
 * the collected statistics for one table or NULL. NULL doesn't mean
 * that the table doesn't exist, just that there are no statistics, so the
 * caller is better off to report ZERO instead.
 */
PgStat_StatTabEntry *
pgstat_fetch_stat_tabentry(Oid relid)
{
    return pgstat_fetch_stat_tabentry_ext(IsSharedRelation(relid), relid);
}
 
/*
 * More efficient version of pgstat_fetch_stat_tabentry(), allowing to specify
 * whether the to-be-accessed table is a shared relation or not.
 */
PgStat_StatTabEntry *
pgstat_fetch_stat_tabentry_ext(bool shared, Oid reloid)
{
    Oid         dboid = (shared ? InvalidOid : MyDatabaseId);
 
    return (PgStat_StatTabEntry *)
        pgstat_fetch_entry(PGSTAT_KIND_RELATION, dboid, reloid);
}
 
/*
 * find any existing PgStat_TableStatus entry for rel
 *
 * Find any existing PgStat_TableStatus entry for rel_id in the current
 * database. If not found, try finding from shared tables.
 *
 * If an entry is found, copy it and increment the copy's counters with their
 * subtransaction counterparts, then return the copy.  The caller may need to
 * pfree() the copy.
 *
 * If no entry found, return NULL, don't create a new one.
 */
PgStat_TableStatus *
find_tabstat_entry(Oid rel_id)
{
    PgStat_EntryRef *entry_ref;
    PgStat_TableXactStatus *trans;
    PgStat_TableStatus *tabentry = NULL;
    PgStat_TableStatus *tablestatus = NULL;
 
    entry_ref = pgstat_fetch_pending_entry(PGSTAT_KIND_RELATION, MyDatabaseId, rel_id);
    if (!entry_ref)
    {
        entry_ref = pgstat_fetch_pending_entry(PGSTAT_KIND_RELATION, InvalidOid, rel_id);
        if (!entry_ref)
            return tablestatus;
    }
 
    tabentry = (PgStat_TableStatus *) entry_ref->pending;
    tablestatus = palloc(sizeof(PgStat_TableStatus));
    *tablestatus = *tabentry;
 
    /*
     * Reset tablestatus->trans in the copy of PgStat_TableStatus as it may
     * point to a shared memory area.  Its data is saved below, so removing it
     * does not matter.
     */
    tablestatus->trans = NULL;
 
    /*
     * Live subtransaction counts are not included yet.  This is not a hot
     * code path so reconcile tuples_inserted, tuples_updated and
     * tuples_deleted even if the caller may not be interested in this data.
     */
    for (trans = tabentry->trans; trans != NULL; trans = trans->upper)
    {
        tablestatus->counts.tuples_inserted += trans->tuples_inserted;
        tablestatus->counts.tuples_updated += trans->tuples_updated;
        tablestatus->counts.tuples_deleted += trans->tuples_deleted;
    }
 
    return tablestatus;
}
 
/*
 * Perform relation stats specific end-of-transaction work. Helper for
 * AtEOXact_PgStat.
 *
 * Transfer transactional insert/update counts into the base tabstat entries.
 * We don't bother to free any of the transactional state, since it's all in
 * TopTransactionContext and will go away anyway.
 */
void
AtEOXact_PgStat_Relations(PgStat_SubXactStatus *xact_state, bool isCommit)
{
    PgStat_TableXactStatus *trans;
 
    for (trans = xact_state->first; trans != NULL; trans = trans->next)
    {
        PgStat_TableStatus *tabstat;
 
        Assert(trans->nest_level == 1);
        Assert(trans->upper == NULL);
        tabstat = trans->parent;
        Assert(tabstat->trans == trans);
        /* restore pre-truncate/drop stats (if any) in case of aborted xact */
        if (!isCommit)
            restore_truncdrop_counters(trans);
        /* count attempted actions regardless of commit/abort */
        tabstat->counts.tuples_inserted += trans->tuples_inserted;
        tabstat->counts.tuples_updated += trans->tuples_updated;
        tabstat->counts.tuples_deleted += trans->tuples_deleted;
        if (isCommit)
        {
            tabstat->counts.truncdropped = trans->truncdropped;
            if (trans->truncdropped)
            {
                /* forget live/dead stats seen by backend thus far */
                tabstat->counts.delta_live_tuples = 0;
                tabstat->counts.delta_dead_tuples = 0;
            }
            /* insert adds a live tuple, delete removes one */
            tabstat->counts.delta_live_tuples +=
                trans->tuples_inserted - trans->tuples_deleted;
            /* update and delete each create a dead tuple */
            tabstat->counts.delta_dead_tuples +=
                trans->tuples_updated + trans->tuples_deleted;
            /* insert, update, delete each count as one change event */
            tabstat->counts.changed_tuples +=
                trans->tuples_inserted + trans->tuples_updated +
                trans->tuples_deleted;
        }
        else
        {
            /* inserted tuples are dead, deleted tuples are unaffected */
            tabstat->counts.delta_dead_tuples +=
                trans->tuples_inserted + trans->tuples_updated;
            /* an aborted xact generates no changed_tuple events */
        }
        tabstat->trans = NULL;
    }
}
 
/*
 * Perform relation stats specific end-of-sub-transaction work. Helper for
 * AtEOSubXact_PgStat.
 *
 * Transfer transactional insert/update counts into the next higher
 * subtransaction state.
 */
void
AtEOSubXact_PgStat_Relations(PgStat_SubXactStatus *xact_state, bool isCommit, int nestDepth)
{
    PgStat_TableXactStatus *trans;
    PgStat_TableXactStatus *next_trans;
 
    for (trans = xact_state->first; trans != NULL; trans = next_trans)
    {
        PgStat_TableStatus *tabstat;
 
        next_trans = trans->next;
        Assert(trans->nest_level == nestDepth);
        tabstat = trans->parent;
        Assert(tabstat->trans == trans);
 
        if (isCommit)
        {
            if (trans->upper && trans->upper->nest_level == nestDepth - 1)
            {
                if (trans->truncdropped)
                {
                    /* propagate the truncate/drop status one level up */
                    save_truncdrop_counters(trans->upper, false);
                    /* replace upper xact stats with ours */
                    trans->upper->tuples_inserted = trans->tuples_inserted;
                    trans->upper->tuples_updated = trans->tuples_updated;
                    trans->upper->tuples_deleted = trans->tuples_deleted;
                }
                else
                {
                    trans->upper->tuples_inserted += trans->tuples_inserted;
                    trans->upper->tuples_updated += trans->tuples_updated;
                    trans->upper->tuples_deleted += trans->tuples_deleted;
                }
                tabstat->trans = trans->upper;
                pfree(trans);
            }
            else
            {
                /*
                 * When there isn't an immediate parent state, we can just
                 * reuse the record instead of going through a palloc/pfree
                 * pushup (this works since it's all in TopTransactionContext
                 * anyway).  We have to re-link it into the parent level,
                 * though, and that might mean pushing a new entry into the
                 * pgStatXactStack.
                 */
                PgStat_SubXactStatus *upper_xact_state;
 
                upper_xact_state = pgstat_get_xact_stack_level(nestDepth - 1);
                trans->next = upper_xact_state->first;
                upper_xact_state->first = trans;
                trans->nest_level = nestDepth - 1;
            }
        }
        else
        {
            /*
             * On abort, update top-level tabstat counts, then forget the
             * subtransaction
             */
 
            /* first restore values obliterated by truncate/drop */
            restore_truncdrop_counters(trans);
            /* count attempted actions regardless of commit/abort */
            tabstat->counts.tuples_inserted += trans->tuples_inserted;
            tabstat->counts.tuples_updated += trans->tuples_updated;
            tabstat->counts.tuples_deleted += trans->tuples_deleted;
            /* inserted tuples are dead, deleted tuples are unaffected */
            tabstat->counts.delta_dead_tuples +=
                trans->tuples_inserted + trans->tuples_updated;
            tabstat->trans = trans->upper;
            pfree(trans);
        }
    }
}
 
/*
 * Generate 2PC records for all the pending transaction-dependent relation
 * stats.
 */
void
AtPrepare_PgStat_Relations(PgStat_SubXactStatus *xact_state)
{
    PgStat_TableXactStatus *trans;
 
    for (trans = xact_state->first; trans != NULL; trans = trans->next)
    {
        PgStat_TableStatus *tabstat PG_USED_FOR_ASSERTS_ONLY;
        TwoPhasePgStatRecord record;
 
        Assert(trans->nest_level == 1);
        Assert(trans->upper == NULL);
        tabstat = trans->parent;
        Assert(tabstat->trans == trans);
 
        record.tuples_inserted = trans->tuples_inserted;
        record.tuples_updated = trans->tuples_updated;
        record.tuples_deleted = trans->tuples_deleted;
        record.inserted_pre_truncdrop = trans->inserted_pre_truncdrop;
        record.updated_pre_truncdrop = trans->updated_pre_truncdrop;
        record.deleted_pre_truncdrop = trans->deleted_pre_truncdrop;
        record.id = tabstat->id;
        record.shared = tabstat->shared;
        record.truncdropped = trans->truncdropped;
 
        RegisterTwoPhaseRecord(TWOPHASE_RM_PGSTAT_ID, 0,
                               &record, sizeof(TwoPhasePgStatRecord));
    }
}
 
/*
 * All we need do here is unlink the transaction stats state from the
 * nontransactional state.  The nontransactional action counts will be
 * reported to the stats system immediately, while the effects on live and
 * dead tuple counts are preserved in the 2PC state file.
 *
 * Note: AtEOXact_PgStat_Relations is not called during PREPARE.
 */
void
PostPrepare_PgStat_Relations(PgStat_SubXactStatus *xact_state)
{
    PgStat_TableXactStatus *trans;
 
    for (trans = xact_state->first; trans != NULL; trans = trans->next)
    {
        PgStat_TableStatus *tabstat;
 
        tabstat = trans->parent;
        tabstat->trans = NULL;
    }
}
 
/*
 * 2PC processing routine for COMMIT PREPARED case.
 *
 * Load the saved counts into our local pgstats state.
 */
void
pgstat_twophase_postcommit(TransactionId xid, uint16 info,
                           void *recdata, uint32 len)
{
    TwoPhasePgStatRecord *rec = (TwoPhasePgStatRecord *) recdata;
    PgStat_TableStatus *pgstat_info;
 
    /* Find or create a tabstat entry for the rel */
    pgstat_info = pgstat_prep_relation_pending(rec->id, rec->shared);
 
    /* Same math as in AtEOXact_PgStat, commit case */
    pgstat_info->counts.tuples_inserted += rec->tuples_inserted;
    pgstat_info->counts.tuples_updated += rec->tuples_updated;
    pgstat_info->counts.tuples_deleted += rec->tuples_deleted;
    pgstat_info->counts.truncdropped = rec->truncdropped;
    if (rec->truncdropped)
    {
        /* forget live/dead stats seen by backend thus far */
        pgstat_info->counts.delta_live_tuples = 0;
        pgstat_info->counts.delta_dead_tuples = 0;
    }
    pgstat_info->counts.delta_live_tuples +=
        rec->tuples_inserted - rec->tuples_deleted;
    pgstat_info->counts.delta_dead_tuples +=
        rec->tuples_updated + rec->tuples_deleted;
    pgstat_info->counts.changed_tuples +=
        rec->tuples_inserted + rec->tuples_updated +
        rec->tuples_deleted;
}
 
/*
 * 2PC processing routine for ROLLBACK PREPARED case.
 *
 * Load the saved counts into our local pgstats state, but treat them
 * as aborted.
 */
void
pgstat_twophase_postabort(TransactionId xid, uint16 info,
                          void *recdata, uint32 len)
{
    TwoPhasePgStatRecord *rec = (TwoPhasePgStatRecord *) recdata;
    PgStat_TableStatus *pgstat_info;
 
    /* Find or create a tabstat entry for the rel */
    pgstat_info = pgstat_prep_relation_pending(rec->id, rec->shared);
 
    /* Same math as in AtEOXact_PgStat, abort case */
    if (rec->truncdropped)
    {
        rec->tuples_inserted = rec->inserted_pre_truncdrop;
        rec->tuples_updated = rec->updated_pre_truncdrop;
        rec->tuples_deleted = rec->deleted_pre_truncdrop;
    }
    pgstat_info->counts.tuples_inserted += rec->tuples_inserted;
    pgstat_info->counts.tuples_updated += rec->tuples_updated;
    pgstat_info->counts.tuples_deleted += rec->tuples_deleted;
    pgstat_info->counts.delta_dead_tuples +=
        rec->tuples_inserted + rec->tuples_updated;
}
 
/*
 * Flush out pending stats for the entry
 *
 * If nowait is true, this function returns false if lock could not
 * immediately acquired, otherwise true is returned.
 *
 * Some of the stats are copied to the corresponding pending database stats
 * entry when successfully flushing.
 */
bool
pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
{
    static const PgStat_TableCounts all_zeroes;
    Oid         dboid;
    PgStat_TableStatus *lstats; /* pending stats entry  */
    PgStatShared_Relation *shtabstats;
    PgStat_StatTabEntry *tabentry;  /* table entry of shared stats */
    PgStat_StatDBEntry *dbentry;    /* pending database entry */
 
    dboid = entry_ref->shared_entry->key.dboid;
    lstats = (PgStat_TableStatus *) entry_ref->pending;
    shtabstats = (PgStatShared_Relation *) entry_ref->shared_stats;
 
    /*
     * Ignore entries that didn't accumulate any actual counts, such as
     * indexes that were opened by the planner but not used.
     */
    if (memcmp(&lstats->counts, &all_zeroes,
               sizeof(PgStat_TableCounts)) == 0)
    {
        return true;
    }
 
    if (!pgstat_lock_entry(entry_ref, nowait))
        return false;
 
    /* add the values to the shared entry. */
    tabentry = &shtabstats->stats;
 
    tabentry->numscans += lstats->counts.numscans;
    if (lstats->counts.numscans)
    {
        TimestampTz t = GetCurrentTransactionStopTimestamp();
 
        if (t > tabentry->lastscan)
            tabentry->lastscan = t;
    }
    tabentry->tuples_returned += lstats->counts.tuples_returned;
    tabentry->tuples_fetched += lstats->counts.tuples_fetched;
    tabentry->tuples_inserted += lstats->counts.tuples_inserted;
    tabentry->tuples_updated += lstats->counts.tuples_updated;
    tabentry->tuples_deleted += lstats->counts.tuples_deleted;
    tabentry->tuples_hot_updated += lstats->counts.tuples_hot_updated;
    tabentry->tuples_newpage_updated += lstats->counts.tuples_newpage_updated;
 
    /*
     * If table was truncated/dropped, first reset the live/dead counters.
     */
    if (lstats->counts.truncdropped)
    {
        tabentry->live_tuples = 0;
        tabentry->dead_tuples = 0;
        tabentry->ins_since_vacuum = 0;
    }
 
    tabentry->live_tuples += lstats->counts.delta_live_tuples;
    tabentry->dead_tuples += lstats->counts.delta_dead_tuples;
    tabentry->mod_since_analyze += lstats->counts.changed_tuples;
    tabentry->ins_since_vacuum += lstats->counts.tuples_inserted;
    tabentry->blocks_fetched += lstats->counts.blocks_fetched;
    tabentry->blocks_hit += lstats->counts.blocks_hit;
 
    /* Clamp live_tuples in case of negative delta_live_tuples */
    tabentry->live_tuples = Max(tabentry->live_tuples, 0);
    /* Likewise for dead_tuples */
    tabentry->dead_tuples = Max(tabentry->dead_tuples, 0);
 
    pgstat_unlock_entry(entry_ref);
 
    /* The entry was successfully flushed, add the same to database stats */
    dbentry = pgstat_prep_database_pending(dboid);
    dbentry->tuples_returned += lstats->counts.tuples_returned;
    dbentry->tuples_fetched += lstats->counts.tuples_fetched;
    dbentry->tuples_inserted += lstats->counts.tuples_inserted;
    dbentry->tuples_updated += lstats->counts.tuples_updated;
    dbentry->tuples_deleted += lstats->counts.tuples_deleted;
    dbentry->blocks_fetched += lstats->counts.blocks_fetched;
    dbentry->blocks_hit += lstats->counts.blocks_hit;
 
    return true;
}
 
void
pgstat_relation_delete_pending_cb(PgStat_EntryRef *entry_ref)
{
    PgStat_TableStatus *pending = (PgStat_TableStatus *) entry_ref->pending;
 
    if (pending->relation)
        pgstat_unlink_relation(pending->relation);
}
 
/*
 * Find or create a PgStat_TableStatus entry for rel. New entry is created and
 * initialized if not exists.
 */
static PgStat_TableStatus *
pgstat_prep_relation_pending(Oid rel_id, bool isshared)
{
    PgStat_EntryRef *entry_ref;
    PgStat_TableStatus *pending;
 
    entry_ref = pgstat_prep_pending_entry(PGSTAT_KIND_RELATION,
                                          isshared ? InvalidOid : MyDatabaseId,
                                          rel_id, NULL);
    pending = entry_ref->pending;
    pending->id = rel_id;
    pending->shared = isshared;
 
    return pending;
}
 
/*
 * add a new (sub)transaction state record
 */
static void
add_tabstat_xact_level(PgStat_TableStatus *pgstat_info, int nest_level)
{
    PgStat_SubXactStatus *xact_state;
    PgStat_TableXactStatus *trans;
 
    /*
     * If this is the first rel to be modified at the current nest level, we
     * first have to push a transaction stack entry.
     */
    xact_state = pgstat_get_xact_stack_level(nest_level);
 
    /* Now make a per-table stack entry */
    trans = (PgStat_TableXactStatus *)
        MemoryContextAllocZero(TopTransactionContext,
                               sizeof(PgStat_TableXactStatus));
    trans->nest_level = nest_level;
    trans->upper = pgstat_info->trans;
    trans->parent = pgstat_info;
    trans->next = xact_state->first;
    xact_state->first = trans;
    pgstat_info->trans = trans;
}
 
/*
 * Add a new (sub)transaction record if needed.
 */
static void
ensure_tabstat_xact_level(PgStat_TableStatus *pgstat_info)
{
    int         nest_level = GetCurrentTransactionNestLevel();
 
    if (pgstat_info->trans == NULL ||
        pgstat_info->trans->nest_level != nest_level)
        add_tabstat_xact_level(pgstat_info, nest_level);
}
 
/*
 * Whenever a table is truncated/dropped, we save its i/u/d counters so that
 * they can be cleared, and if the (sub)xact that executed the truncate/drop
 * later aborts, the counters can be restored to the saved (pre-truncate/drop)
 * values.
 *
 * Note that for truncate we do this on the first truncate in any particular
 * subxact level only.
 */
static void
save_truncdrop_counters(PgStat_TableXactStatus *trans, bool is_drop)
{
    if (!trans->truncdropped || is_drop)
    {
        trans->inserted_pre_truncdrop = trans->tuples_inserted;
        trans->updated_pre_truncdrop = trans->tuples_updated;
        trans->deleted_pre_truncdrop = trans->tuples_deleted;
        trans->truncdropped = true;
    }
}
 
/*
 * restore counters when a truncate aborts
 */
static void
restore_truncdrop_counters(PgStat_TableXactStatus *trans)
{
    if (trans->truncdropped)
    {
        trans->tuples_inserted = trans->inserted_pre_truncdrop;
        trans->tuples_updated = trans->updated_pre_truncdrop;
        trans->tuples_deleted = trans->deleted_pre_truncdrop;
    }
}