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       65384 : pgstat_report_wal(bool force)
      47             : {
      48             :     bool        nowait;
      49             : 
      50             :     /* like in pgstat.c, don't wait for lock acquisition when !force */
      51       65384 :     nowait = !force;
      52             : 
      53             :     /* flush wal stats */
      54       65384 :     (void) pgstat_wal_flush_cb(nowait);
      55       65384 :     pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_WAL);
      56             : 
      57             :     /* flush IO stats */
      58       65384 :     pgstat_flush_io(nowait);
      59       65384 :     (void) pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_IO);
      60       65384 : }
      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          70 : pgstat_fetch_stat_wal(void)
      68             : {
      69          70 :     pgstat_snapshot_fixed(PGSTAT_KIND_WAL);
      70             : 
      71          70 :     return &pgStatLocal.snapshot.wal;
      72             : }
      73             : 
      74             : /*
      75             :  * To determine whether WAL usage happened.
      76             :  */
      77             : static inline bool
      78      134922 : pgstat_wal_have_pending(void)
      79             : {
      80      134922 :     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      134922 : pgstat_wal_flush_cb(bool nowait)
      92             : {
      93      134922 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
      94      134922 :     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      134922 :     if (!pgstat_wal_have_pending())
     105      113196 :         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       21726 :     WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevWalUsage);
     113             : 
     114       21726 :     if (!nowait)
     115       18472 :         LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     116        3254 :     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       21726 :     WALSTAT_ACC(wal_records, wal_usage_diff);
     122       21726 :     WALSTAT_ACC(wal_fpi, wal_usage_diff);
     123       21726 :     WALSTAT_ACC(wal_bytes, wal_usage_diff);
     124       21726 :     WALSTAT_ACC(wal_fpi_bytes, wal_usage_diff);
     125       21726 :     WALSTAT_ACC(wal_buffers_full, wal_usage_diff);
     126             : #undef WALSTAT_ACC
     127             : 
     128       21726 :     LWLockRelease(&stats_shmem->lock);
     129             : 
     130             :     /*
     131             :      * Save the current counters for the subsequent calculation of WAL usage.
     132             :      */
     133       21726 :     prevWalUsage = pgWalUsage;
     134             : 
     135       21726 :     return false;
     136             : }
     137             : 
     138             : void
     139       44706 : pgstat_wal_init_backend_cb(void)
     140             : {
     141             :     /*
     142             :      * Initialize prevWalUsage with pgWalUsage so that pgstat_wal_flush_cb()
     143             :      * can calculate how much pgWalUsage counters are increased by subtracting
     144             :      * prevWalUsage from pgWalUsage.
     145             :      */
     146       44706 :     prevWalUsage = pgWalUsage;
     147       44706 : }
     148             : 
     149             : void
     150        2194 : pgstat_wal_init_shmem_cb(void *stats)
     151             : {
     152        2194 :     PgStatShared_Wal *stats_shmem = (PgStatShared_Wal *) stats;
     153             : 
     154        2194 :     LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
     155        2194 : }
     156             : 
     157             : void
     158         468 : pgstat_wal_reset_all_cb(TimestampTz ts)
     159             : {
     160         468 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     161             : 
     162         468 :     LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     163         468 :     memset(&stats_shmem->stats, 0, sizeof(stats_shmem->stats));
     164         468 :     stats_shmem->stats.stat_reset_timestamp = ts;
     165         468 :     LWLockRelease(&stats_shmem->lock);
     166         468 : }
     167             : 
     168             : void
     169        1428 : pgstat_wal_snapshot_cb(void)
     170             : {
     171        1428 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     172             : 
     173        1428 :     LWLockAcquire(&stats_shmem->lock, LW_SHARED);
     174        1428 :     memcpy(&pgStatLocal.snapshot.wal, &stats_shmem->stats,
     175             :            sizeof(pgStatLocal.snapshot.wal));
     176        1428 :     LWLockRelease(&stats_shmem->lock);
     177        1428 : }