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) 2001-2026, 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        13308 : pgstat_report_bgwriter(void)
      32              : {
      33        13308 :     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        13308 :     if (pg_memory_is_all_zeros(&PendingBgWriterStats,
      43              :                                sizeof(struct PgStat_BgWriterStats)))
      44         5889 :         return;
      45              : 
      46         7419 :     pgstat_begin_changecount_write(&stats_shmem->changecount);
      47              : 
      48              : #define BGWRITER_ACC(fld) stats_shmem->stats.fld += PendingBgWriterStats.fld
      49         7419 :     BGWRITER_ACC(buf_written_clean);
      50         7419 :     BGWRITER_ACC(maxwritten_clean);
      51         7419 :     BGWRITER_ACC(buf_alloc);
      52              : #undef BGWRITER_ACC
      53              : 
      54         7419 :     pgstat_end_changecount_write(&stats_shmem->changecount);
      55              : 
      56              :     /*
      57              :      * Clear out the statistics buffer, so it can be re-used.
      58              :      */
      59        37095 :     MemSet(&PendingBgWriterStats, 0, sizeof(PendingBgWriterStats));
      60              : 
      61              :     /*
      62              :      * Report IO statistics
      63              :      */
      64         7419 :     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            6 : pgstat_fetch_stat_bgwriter(void)
      73              : {
      74            6 :     pgstat_snapshot_fixed(PGSTAT_KIND_BGWRITER);
      75              : 
      76            6 :     return &pgStatLocal.snapshot.bgwriter;
      77              : }
      78              : 
      79              : void
      80         1140 : pgstat_bgwriter_init_shmem_cb(void *stats)
      81              : {
      82         1140 :     PgStatShared_BgWriter *stats_shmem = (PgStatShared_BgWriter *) stats;
      83              : 
      84         1140 :     LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
      85         1140 : }
      86              : 
      87              : void
      88          242 : pgstat_bgwriter_reset_all_cb(TimestampTz ts)
      89              : {
      90          242 :     PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
      91              : 
      92              :     /* see explanation above PgStatShared_BgWriter for the reset protocol */
      93          242 :     LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
      94          242 :     pgstat_copy_changecounted_stats(&stats_shmem->reset_offset,
      95          242 :                                     &stats_shmem->stats,
      96              :                                     sizeof(stats_shmem->stats),
      97              :                                     &stats_shmem->changecount);
      98          242 :     stats_shmem->stats.stat_reset_timestamp = ts;
      99          242 :     LWLockRelease(&stats_shmem->lock);
     100          242 : }
     101              : 
     102              : void
     103          716 : pgstat_bgwriter_snapshot_cb(void)
     104              : {
     105          716 :     PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
     106          716 :     PgStat_BgWriterStats *reset_offset = &stats_shmem->reset_offset;
     107              :     PgStat_BgWriterStats reset;
     108              : 
     109          716 :     pgstat_copy_changecounted_stats(&pgStatLocal.snapshot.bgwriter,
     110          716 :                                     &stats_shmem->stats,
     111              :                                     sizeof(stats_shmem->stats),
     112              :                                     &stats_shmem->changecount);
     113              : 
     114          716 :     LWLockAcquire(&stats_shmem->lock, LW_SHARED);
     115          716 :     memcpy(&reset, reset_offset, sizeof(stats_shmem->stats));
     116          716 :     LWLockRelease(&stats_shmem->lock);
     117              : 
     118              :     /* compensate by reset offsets */
     119              : #define BGWRITER_COMP(fld) pgStatLocal.snapshot.bgwriter.fld -= reset.fld;
     120          716 :     BGWRITER_COMP(buf_written_clean);
     121          716 :     BGWRITER_COMP(maxwritten_clean);
     122          716 :     BGWRITER_COMP(buf_alloc);
     123              : #undef BGWRITER_COMP
     124          716 : }