Line data    Source code

       1             : /* -------------------------------------------------------------------------
       2             :  *
       3             :  * pgstat_wal.c
       4             :  *    Implementation of WAL statistics.
       5             :  *
       6             :  * This file contains the implementation of WAL statistics. It is kept
       7             :  * separate from pgstat.c to enforce the line between the statistics access /
       8             :  * storage implementation and the details about individual types of
       9             :  * statistics.
      10             :  *
      11             :  * Copyright (c) 2001-2025, PostgreSQL Global Development Group
      12             :  *
      13             :  * IDENTIFICATION
      14             :  *    src/backend/utils/activity/pgstat_wal.c
      15             :  * -------------------------------------------------------------------------
      16             :  */
      17             : 
      18             : #include "postgres.h"
      19             : 
      20             : #include "executor/instrument.h"
      21             : #include "utils/pgstat_internal.h"
      22             : 
      23             : 
      24             : /*
      25             :  * WAL usage counters saved from pgWalUsage at the previous call to
      26             :  * pgstat_report_wal(). This is used to calculate how much WAL usage
      27             :  * happens between pgstat_report_wal() calls, by subtracting
      28             :  * the previous counters from the current ones.
      29             :  */
      30             : static WalUsage prevWalUsage;
      31             : 
      32             : 
      33             : /*
      34             :  * Calculate how much WAL usage counters have increased and update
      35             :  * shared WAL and IO statistics.
      36             :  *
      37             :  * Must be called by processes that generate WAL, that do not call
      38             :  * pgstat_report_stat(), like walwriter.
      39             :  *
      40             :  * "force" set to true ensures that the statistics are flushed; note that
      41             :  * this needs to acquire the pgstat shmem LWLock, waiting on it.  When
      42             :  * set to false, the statistics may not be flushed if the lock could not
      43             :  * be acquired.
      44             :  */
      45             : void
      46       63942 : pgstat_report_wal(bool force)
      47             : {
      48             :     bool        nowait;
      49             : 
      50             :     /* like in pgstat.c, don't wait for lock acquisition when !force */
      51       63942 :     nowait = !force;
      52             : 
      53             :     /* flush wal stats */
      54       63942 :     (void) pgstat_wal_flush_cb(nowait);
      55       63942 :     pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_WAL);
      56             : 
      57             :     /* flush IO stats */
      58       63942 :     pgstat_flush_io(nowait);
      59       63942 :     (void) pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_IO);
      60       63942 : }
      61             : 
      62             : /*
      63             :  * Support function for the SQL-callable pgstat* functions. Returns
      64             :  * a pointer to the WAL statistics struct.
      65             :  */
      66             : PgStat_WalStats *
      67          68 : pgstat_fetch_stat_wal(void)
      68             : {
      69          68 :     pgstat_snapshot_fixed(PGSTAT_KIND_WAL);
      70             : 
      71          68 :     return &pgStatLocal.snapshot.wal;
      72             : }
      73             : 
      74             : /*
      75             :  * To determine whether WAL usage happened.
      76             :  */
      77             : static inline bool
      78      131308 : pgstat_wal_have_pending(void)
      79             : {
      80      131308 :     return pgWalUsage.wal_records != prevWalUsage.wal_records;
      81             : }
      82             : 
      83             : /*
      84             :  * Calculate how much WAL usage counters have increased by subtracting the
      85             :  * previous counters from the current ones.
      86             :  *
      87             :  * If nowait is true, this function returns true if the lock could not be
      88             :  * acquired. Otherwise return false.
      89             :  */
      90             : bool
      91      131308 : pgstat_wal_flush_cb(bool nowait)
      92             : {
      93      131308 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
      94      131308 :     WalUsage    wal_usage_diff = {0};
      95             : 
      96             :     Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
      97             :     Assert(pgStatLocal.shmem != NULL &&
      98             :            !pgStatLocal.shmem->is_shutdown);
      99             : 
     100             :     /*
     101             :      * This function can be called even if nothing at all has happened. Avoid
     102             :      * taking lock for nothing in that case.
     103             :      */
     104      131308 :     if (!pgstat_wal_have_pending())
     105      109922 :         return false;
     106             : 
     107             :     /*
     108             :      * We don't update the WAL usage portion of the local WalStats elsewhere.
     109             :      * Calculate how much WAL usage counters were increased by subtracting the
     110             :      * previous counters from the current ones.
     111             :      */
     112       21386 :     WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevWalUsage);
     113             : 
     114       21386 :     if (!nowait)
     115       17882 :         LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     116        3504 :     else if (!LWLockConditionalAcquire(&stats_shmem->lock, LW_EXCLUSIVE))
     117           0 :         return true;
     118             : 
     119             : #define WALSTAT_ACC(fld, var_to_add) \
     120             :     (stats_shmem->stats.wal_counters.fld += var_to_add.fld)
     121       21386 :     WALSTAT_ACC(wal_records, wal_usage_diff);
     122       21386 :     WALSTAT_ACC(wal_fpi, wal_usage_diff);
     123       21386 :     WALSTAT_ACC(wal_bytes, wal_usage_diff);
     124       21386 :     WALSTAT_ACC(wal_buffers_full, wal_usage_diff);
     125             : #undef WALSTAT_ACC
     126             : 
     127       21386 :     LWLockRelease(&stats_shmem->lock);
     128             : 
     129             :     /*
     130             :      * Save the current counters for the subsequent calculation of WAL usage.
     131             :      */
     132       21386 :     prevWalUsage = pgWalUsage;
     133             : 
     134       21386 :     return false;
     135             : }
     136             : 
     137             : void
     138       42866 : pgstat_wal_init_backend_cb(void)
     139             : {
     140             :     /*
     141             :      * Initialize prevWalUsage with pgWalUsage so that pgstat_wal_flush_cb()
     142             :      * can calculate how much pgWalUsage counters are increased by subtracting
     143             :      * prevWalUsage from pgWalUsage.
     144             :      */
     145       42866 :     prevWalUsage = pgWalUsage;
     146       42866 : }
     147             : 
     148             : void
     149        2136 : pgstat_wal_init_shmem_cb(void *stats)
     150             : {
     151        2136 :     PgStatShared_Wal *stats_shmem = (PgStatShared_Wal *) stats;
     152             : 
     153        2136 :     LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
     154        2136 : }
     155             : 
     156             : void
     157         470 : pgstat_wal_reset_all_cb(TimestampTz ts)
     158             : {
     159         470 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     160             : 
     161         470 :     LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     162         470 :     memset(&stats_shmem->stats, 0, sizeof(stats_shmem->stats));
     163         470 :     stats_shmem->stats.stat_reset_timestamp = ts;
     164         470 :     LWLockRelease(&stats_shmem->lock);
     165         470 : }
     166             : 
     167             : void
     168        1368 : pgstat_wal_snapshot_cb(void)
     169             : {
     170        1368 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     171             : 
     172        1368 :     LWLockAcquire(&stats_shmem->lock, LW_SHARED);
     173        1368 :     memcpy(&pgStatLocal.snapshot.wal, &stats_shmem->stats,
     174             :            sizeof(pgStatLocal.snapshot.wal));
     175        1368 :     LWLockRelease(&stats_shmem->lock);
     176        1368 : }