Line data    Source code

       1             : /* -------------------------------------------------------------------------
       2             :  *
       3             :  * pgstat_bgwriter.c
       4             :  *    Implementation of bgwriter statistics.
       5             :  *
       6             :  * This file contains the implementation of bgwriter 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_bgwriter.c
      15             :  * -------------------------------------------------------------------------
      16             :  */
      17             : 
      18             : #include "postgres.h"
      19             : 
      20             : #include "utils/memutils.h"
      21             : #include "utils/pgstat_internal.h"
      22             : 
      23             : 
      24             : PgStat_BgWriterStats PendingBgWriterStats = {0};
      25             : 
      26             : 
      27             : /*
      28             :  * Report bgwriter and IO statistics
      29             :  */
      30             : void
      31       19528 : pgstat_report_bgwriter(void)
      32             : {
      33       19528 :     PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
      34             : 
      35             :     Assert(!pgStatLocal.shmem->is_shutdown);
      36             :     pgstat_assert_is_up();
      37             : 
      38             :     /*
      39             :      * This function can be called even if nothing at all has happened. In
      40             :      * this case, avoid unnecessarily modifying the stats entry.
      41             :      */
      42       19528 :     if (pg_memory_is_all_zeros(&PendingBgWriterStats,
      43             :                                sizeof(struct PgStat_BgWriterStats)))
      44        8462 :         return;
      45             : 
      46       11066 :     pgstat_begin_changecount_write(&stats_shmem->changecount);
      47             : 
      48             : #define BGWRITER_ACC(fld) stats_shmem->stats.fld += PendingBgWriterStats.fld
      49       11066 :     BGWRITER_ACC(buf_written_clean);
      50       11066 :     BGWRITER_ACC(maxwritten_clean);
      51       11066 :     BGWRITER_ACC(buf_alloc);
      52             : #undef BGWRITER_ACC
      53             : 
      54       11066 :     pgstat_end_changecount_write(&stats_shmem->changecount);
      55             : 
      56             :     /*
      57             :      * Clear out the statistics buffer, so it can be re-used.
      58             :      */
      59       55330 :     MemSet(&PendingBgWriterStats, 0, sizeof(PendingBgWriterStats));
      60             : 
      61             :     /*
      62             :      * Report IO statistics
      63             :      */
      64       11066 :     pgstat_flush_io(false);
      65             : }
      66             : 
      67             : /*
      68             :  * Support function for the SQL-callable pgstat* functions. Returns
      69             :  * a pointer to the bgwriter statistics struct.
      70             :  */
      71             : PgStat_BgWriterStats *
      72          12 : pgstat_fetch_stat_bgwriter(void)
      73             : {
      74          12 :     pgstat_snapshot_fixed(PGSTAT_KIND_BGWRITER);
      75             : 
      76          12 :     return &pgStatLocal.snapshot.bgwriter;
      77             : }
      78             : 
      79             : void
      80        2084 : pgstat_bgwriter_init_shmem_cb(void *stats)
      81             : {
      82        2084 :     PgStatShared_BgWriter *stats_shmem = (PgStatShared_BgWriter *) stats;
      83             : 
      84        2084 :     LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
      85        2084 : }
      86             : 
      87             : void
      88         452 : pgstat_bgwriter_reset_all_cb(TimestampTz ts)
      89             : {
      90         452 :     PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
      91             : 
      92             :     /* see explanation above PgStatShared_BgWriter for the reset protocol */
      93         452 :     LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
      94         452 :     pgstat_copy_changecounted_stats(&stats_shmem->reset_offset,
      95         452 :                                     &stats_shmem->stats,
      96             :                                     sizeof(stats_shmem->stats),
      97             :                                     &stats_shmem->changecount);
      98         452 :     stats_shmem->stats.stat_reset_timestamp = ts;
      99         452 :     LWLockRelease(&stats_shmem->lock);
     100         452 : }
     101             : 
     102             : void
     103        1260 : pgstat_bgwriter_snapshot_cb(void)
     104             : {
     105        1260 :     PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
     106        1260 :     PgStat_BgWriterStats *reset_offset = &stats_shmem->reset_offset;
     107             :     PgStat_BgWriterStats reset;
     108             : 
     109        1260 :     pgstat_copy_changecounted_stats(&pgStatLocal.snapshot.bgwriter,
     110        1260 :                                     &stats_shmem->stats,
     111             :                                     sizeof(stats_shmem->stats),
     112             :                                     &stats_shmem->changecount);
     113             : 
     114        1260 :     LWLockAcquire(&stats_shmem->lock, LW_SHARED);
     115        1260 :     memcpy(&reset, reset_offset, sizeof(stats_shmem->stats));
     116        1260 :     LWLockRelease(&stats_shmem->lock);
     117             : 
     118             :     /* compensate by reset offsets */
     119             : #define BGWRITER_COMP(fld) pgStatLocal.snapshot.bgwriter.fld -= reset.fld;
     120        1260 :     BGWRITER_COMP(buf_written_clean);
     121        1260 :     BGWRITER_COMP(maxwritten_clean);
     122        1260 :     BGWRITER_COMP(buf_alloc);
     123             : #undef BGWRITER_COMP
     124        1260 : }