LCOV - code coverage report
Current view: top level - src/backend/utils/activity - pgstat_wal.c (source / functions) Hit Total Coverage
Test: PostgreSQL 17devel Lines: 49 50 98.0 %
Date: 2024-02-28 23:11:08 Functions: 7 7 100.0 %
Legend: Lines: hit not hit

          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) 2001-2024, 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 "utils/pgstat_internal.h"
      21             : #include "executor/instrument.h"
      22             : 
      23             : 
      24             : PgStat_PendingWalStats PendingWalStats = {0};
      25             : 
      26             : /*
      27             :  * WAL usage counters saved from pgWalUsage at the previous call to
      28             :  * pgstat_report_wal(). This is used to calculate how much WAL usage
      29             :  * happens between pgstat_report_wal() calls, by subtracting
      30             :  * the previous counters from the current ones.
      31             :  */
      32             : static WalUsage prevWalUsage;
      33             : 
      34             : 
      35             : /*
      36             :  * Calculate how much WAL usage counters have increased and update
      37             :  * shared WAL and IO statistics.
      38             :  *
      39             :  * Must be called by processes that generate WAL, that do not call
      40             :  * pgstat_report_stat(), like walwriter.
      41             :  *
      42             :  * "force" set to true ensures that the statistics are flushed; note that
      43             :  * this needs to acquire the pgstat shmem LWLock, waiting on it.  When
      44             :  * set to false, the statistics may not be flushed if the lock could not
      45             :  * be acquired.
      46             :  */
      47             : void
      48       34518 : pgstat_report_wal(bool force)
      49             : {
      50             :     bool        nowait;
      51             : 
      52             :     /* like in pgstat.c, don't wait for lock acquisition when !force */
      53       34518 :     nowait = !force;
      54             : 
      55             :     /* flush wal stats */
      56       34518 :     pgstat_flush_wal(nowait);
      57             : 
      58             :     /* flush IO stats */
      59       34518 :     pgstat_flush_io(nowait);
      60       34518 : }
      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             :  * 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       84656 : pgstat_flush_wal(bool nowait)
      83             : {
      84       84656 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
      85       84656 :     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       84656 :     if (!pgstat_have_pending_wal())
      96       67524 :         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       17132 :     WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevWalUsage);
     104             : 
     105       17132 :     if (!nowait)
     106       13344 :         LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     107        3788 :     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.fld += var_to_add.fld)
     112             : #define WALSTAT_ACC_INSTR_TIME(fld) \
     113             :     (stats_shmem->stats.fld += INSTR_TIME_GET_MICROSEC(PendingWalStats.fld))
     114       17132 :     WALSTAT_ACC(wal_records, wal_usage_diff);
     115       17132 :     WALSTAT_ACC(wal_fpi, wal_usage_diff);
     116       17132 :     WALSTAT_ACC(wal_bytes, wal_usage_diff);
     117       17132 :     WALSTAT_ACC(wal_buffers_full, PendingWalStats);
     118       17132 :     WALSTAT_ACC(wal_write, PendingWalStats);
     119       17132 :     WALSTAT_ACC(wal_sync, PendingWalStats);
     120       17132 :     WALSTAT_ACC_INSTR_TIME(wal_write_time);
     121       17132 :     WALSTAT_ACC_INSTR_TIME(wal_sync_time);
     122             : #undef WALSTAT_ACC_INSTR_TIME
     123             : #undef WALSTAT_ACC
     124             : 
     125       17132 :     LWLockRelease(&stats_shmem->lock);
     126             : 
     127             :     /*
     128             :      * Save the current counters for the subsequent calculation of WAL usage.
     129             :      */
     130       17132 :     prevWalUsage = pgWalUsage;
     131             : 
     132             :     /*
     133             :      * Clear out the statistics buffer, so it can be re-used.
     134             :      */
     135      102792 :     MemSet(&PendingWalStats, 0, sizeof(PendingWalStats));
     136             : 
     137       17132 :     return false;
     138             : }
     139             : 
     140             : void
     141       28932 : pgstat_init_wal(void)
     142             : {
     143             :     /*
     144             :      * Initialize prevWalUsage with pgWalUsage so that pgstat_flush_wal() can
     145             :      * calculate how much pgWalUsage counters are increased by subtracting
     146             :      * prevWalUsage from pgWalUsage.
     147             :      */
     148       28932 :     prevWalUsage = pgWalUsage;
     149       28932 : }
     150             : 
     151             : /*
     152             :  * To determine whether any WAL activity has occurred since last time, not
     153             :  * only the number of generated WAL records but also the numbers of WAL
     154             :  * writes and syncs need to be checked. Because even transaction that
     155             :  * generates no WAL records can write or sync WAL data when flushing the
     156             :  * data pages.
     157             :  */
     158             : bool
     159       93448 : pgstat_have_pending_wal(void)
     160             : {
     161      172146 :     return pgWalUsage.wal_records != prevWalUsage.wal_records ||
     162      169754 :         PendingWalStats.wal_write != 0 ||
     163       76306 :         PendingWalStats.wal_sync != 0;
     164             : }
     165             : 
     166             : void
     167         394 : pgstat_wal_reset_all_cb(TimestampTz ts)
     168             : {
     169         394 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     170             : 
     171         394 :     LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
     172         394 :     memset(&stats_shmem->stats, 0, sizeof(stats_shmem->stats));
     173         394 :     stats_shmem->stats.stat_reset_timestamp = ts;
     174         394 :     LWLockRelease(&stats_shmem->lock);
     175         394 : }
     176             : 
     177             : void
     178        1036 : pgstat_wal_snapshot_cb(void)
     179             : {
     180        1036 :     PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
     181             : 
     182        1036 :     LWLockAcquire(&stats_shmem->lock, LW_SHARED);
     183        1036 :     memcpy(&pgStatLocal.snapshot.wal, &stats_shmem->stats,
     184             :            sizeof(pgStatLocal.snapshot.wal));
     185        1036 :     LWLockRelease(&stats_shmem->lock);
     186        1036 : }

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