src/backend/utils/activity/pgstat_bgwriter.c

   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) 2001-2024, 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/pgstat_internal.h"
  21
  22
  23 PgStat_BgWriterStats PendingBgWriterStats = {0};
  24
  25
  26 /*
  27  * Report bgwriter and IO statistics
  28  */
  29 void
  30 pgstat_report_bgwriter(void)
  31 {
  32         PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
  33         static const PgStat_BgWriterStats all_zeroes;
  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         if (memcmp(&PendingBgWriterStats, &all_zeroes, sizeof(all_zeroes)) == 0)
  43                 return;
  44
  45         pgstat_begin_changecount_write(&stats_shmem->changecount);
  46
  47 #define BGWRITER_ACC(fld) stats_shmem->stats.fld += PendingBgWriterStats.fld
  48         BGWRITER_ACC(buf_written_clean);
  49         BGWRITER_ACC(maxwritten_clean);
  50         BGWRITER_ACC(buf_alloc);
  51 #undef BGWRITER_ACC
  52
  53         pgstat_end_changecount_write(&stats_shmem->changecount);
  54
  55         /*
  56          * Clear out the statistics buffer, so it can be re-used.
  57          */
  58         MemSet(&PendingBgWriterStats, 0, sizeof(PendingBgWriterStats));
  59
  60         /*
  61          * Report IO statistics
  62          */
  63         pgstat_flush_io(false);
  64 }
  65
  66 /*
  67  * Support function for the SQL-callable pgstat* functions. Returns
  68  * a pointer to the bgwriter statistics struct.
  69  */
  70 PgStat_BgWriterStats *
  71 pgstat_fetch_stat_bgwriter(void)
  72 {
  73         pgstat_snapshot_fixed(PGSTAT_KIND_BGWRITER);
  74
  75         return &pgStatLocal.snapshot.bgwriter;
  76 }
  77
  78 void
  79 pgstat_bgwriter_init_shmem_cb(void *stats)
  80 {
  81         PgStatShared_BgWriter *stats_shmem = (PgStatShared_BgWriter *) stats;
  82
  83         LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
  84 }
  85
  86 void
  87 pgstat_bgwriter_reset_all_cb(TimestampTz ts)
  88 {
  89         PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
  90
  91         /* see explanation above PgStatShared_BgWriter for the reset protocol */
  92         LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
  93         pgstat_copy_changecounted_stats(&stats_shmem->reset_offset,
  94                                                                         &stats_shmem->stats,
  95                                                                         sizeof(stats_shmem->stats),
  96                                                                         &stats_shmem->changecount);
  97         stats_shmem->stats.stat_reset_timestamp = ts;
  98         LWLockRelease(&stats_shmem->lock);
  99 }
 100
 101 void
 102 pgstat_bgwriter_snapshot_cb(void)
 103 {
 104         PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
 105         PgStat_BgWriterStats *reset_offset = &stats_shmem->reset_offset;
 106         PgStat_BgWriterStats reset;
 107
 108         pgstat_copy_changecounted_stats(&pgStatLocal.snapshot.bgwriter,
 109                                                                         &stats_shmem->stats,
 110                                                                         sizeof(stats_shmem->stats),
 111                                                                         &stats_shmem->changecount);
 112
 113         LWLockAcquire(&stats_shmem->lock, LW_SHARED);
 114         memcpy(&reset, reset_offset, sizeof(stats_shmem->stats));
 115         LWLockRelease(&stats_shmem->lock);
 116
 117         /* compensate by reset offsets */
 118 #define BGWRITER_COMP(fld) pgStatLocal.snapshot.bgwriter.fld -= reset.fld;
 119         BGWRITER_COMP(buf_written_clean);
 120         BGWRITER_COMP(maxwritten_clean);
 121         BGWRITER_COMP(buf_alloc);
 122 #undef BGWRITER_COMP
 123 }