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       44938 : pgstat_report_wal(bool force)
      47             : {
      48             :     bool        nowait;
      49             : 
      50             :     /* like in pgstat.c, don't wait for lock acquisition when !force */
      51       44938 :     nowait = !force;
      52             : 
      53             :     /* flush wal stats */
      54       44938 :     (void) pgstat_wal_flush_cb(nowait);
      55       44938 :     pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_WAL);
      56             : 
      57             :     /* flush IO stats */
      58       44938 :     pgstat_flush_io(nowait);
      59       44938 :     (void) pgstat_flush_backend(nowait, PGSTAT_BACKEND_FLUSH_IO);
      60       44938 : }
      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          72 : pgstat_fetch_stat_wal(void)
      68             : {
      69          72 :     pgstat_snapshot_fixed(PGSTAT_KIND_WAL);
      70             : 
      71          72 :     return &pgStatLocal.snapshot.wal;
      72             : }
      73             : 
      74             : /*
      75             :  * Calculate how much WAL usage counters have increased by subtracting the
      76             :  * previous counters from the current ones.
      77             :  *
      78             :  * If nowait is true, this function returns true if the lock could not be
      79             :  * acquired. Otherwise return false.
      80             :  */
      81             : bool
      82      113636 : pgstat_wal_flush_cb(bool nowait)
      83             : {
      84      113636 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
      85      113636 :     WalUsage    wal_usage_diff = {0};
      86             : 
      87             :     Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
      88             :     Assert(pgStatLocal.shmem != NULL &&
      89             :            !pgStatLocal.shmem->is_shutdown);
      90             : 
      91             :     /*
      92             :      * This function can be called even if nothing at all has happened. Avoid
      93             :      * taking lock for nothing in that case.
      94             :      */
      95      113636 :     if (!pgstat_wal_have_pending_cb())
      96       94518 :         return false;
      97             : 
      98             :     /*
      99             :      * We don't update the WAL usage portion of the local WalStats elsewhere.
     100             :      * Calculate how much WAL usage counters were increased by subtracting the
     101             :      * previous counters from the current ones.
     102             :      */
     103       19118 :     WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevWalUsage);
     104             : 
     105       19118 :     if (!nowait)
     106       16576 :         LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     107        2542 :     else if (!LWLockConditionalAcquire(&stats_shmem->lock, LW_EXCLUSIVE))
     108           0 :         return true;
     109             : 
     110             : #define WALSTAT_ACC(fld, var_to_add) \
     111             :     (stats_shmem->stats.wal_counters.fld += var_to_add.fld)
     112       19118 :     WALSTAT_ACC(wal_records, wal_usage_diff);
     113       19118 :     WALSTAT_ACC(wal_fpi, wal_usage_diff);
     114       19118 :     WALSTAT_ACC(wal_bytes, wal_usage_diff);
     115       19118 :     WALSTAT_ACC(wal_buffers_full, wal_usage_diff);
     116             : #undef WALSTAT_ACC
     117             : 
     118       19118 :     LWLockRelease(&stats_shmem->lock);
     119             : 
     120             :     /*
     121             :      * Save the current counters for the subsequent calculation of WAL usage.
     122             :      */
     123       19118 :     prevWalUsage = pgWalUsage;
     124             : 
     125       19118 :     return false;
     126             : }
     127             : 
     128             : void
     129       42300 : pgstat_wal_init_backend_cb(void)
     130             : {
     131             :     /*
     132             :      * Initialize prevWalUsage with pgWalUsage so that pgstat_wal_flush_cb()
     133             :      * can calculate how much pgWalUsage counters are increased by subtracting
     134             :      * prevWalUsage from pgWalUsage.
     135             :      */
     136       42300 :     prevWalUsage = pgWalUsage;
     137       42300 : }
     138             : 
     139             : /*
     140             :  * To determine whether WAL usage happened.
     141             :  */
     142             : bool
     143      126534 : pgstat_wal_have_pending_cb(void)
     144             : {
     145      126534 :     return pgWalUsage.wal_records != prevWalUsage.wal_records;
     146             : }
     147             : 
     148             : void
     149        2032 : pgstat_wal_init_shmem_cb(void *stats)
     150             : {
     151        2032 :     PgStatShared_Wal *stats_shmem = (PgStatShared_Wal *) stats;
     152             : 
     153        2032 :     LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
     154        2032 : }
     155             : 
     156             : void
     157         448 : pgstat_wal_reset_all_cb(TimestampTz ts)
     158             : {
     159         448 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     160             : 
     161         448 :     LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     162         448 :     memset(&stats_shmem->stats, 0, sizeof(stats_shmem->stats));
     163         448 :     stats_shmem->stats.stat_reset_timestamp = ts;
     164         448 :     LWLockRelease(&stats_shmem->lock);
     165         448 : }
     166             : 
     167             : void
     168        1298 : pgstat_wal_snapshot_cb(void)
     169             : {
     170        1298 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     171             : 
     172        1298 :     LWLockAcquire(&stats_shmem->lock, LW_SHARED);
     173        1298 :     memcpy(&pgStatLocal.snapshot.wal, &stats_shmem->stats,
     174             :            sizeof(pgStatLocal.snapshot.wal));
     175        1298 :     LWLockRelease(&stats_shmem->lock);
     176        1298 : }