/* -------------------------------------------------------------------------

 *

 * pgstat_bgwriter.c

 *    Implementation of bgwriter statistics.

 *

 * This file contains the implementation of bgwriter statistics. It is kept

 * separate from pgstat.c to enforce the line between the statistics access /

 * storage implementation and the details about individual types of

 * statistics.

 *

 * Copyright (c) 2001-2026, PostgreSQL Global Development Group

 *

 * IDENTIFICATION

 *    src/backend/utils/activity/pgstat_bgwriter.c

 * -------------------------------------------------------------------------

 */

#include "postgres.h"

#include "utils/memutils.h"

#include "utils/pgstat_internal.h"

PgStat_BgWriterStats PendingBgWriterStats = {0};

/*

 * Report bgwriter and IO statistics

 */

void

pgstat_report_bgwriter(void)

{

  PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;

  Assert(!pgStatLocal.shmem->is_shutdown);

  pgstat_assert_is_up();

  /*

   * This function can be called even if nothing at all has happened. In

   * this case, avoid unnecessarily modifying the stats entry.

   */

  if (pg_memory_is_all_zeros(&PendingBgWriterStats,

                 sizeof(struct PgStat_BgWriterStats)))

    return;

  pgstat_begin_changecount_write(&stats_shmem->changecount);

#define BGWRITER_ACC(fld) stats_shmem->stats.fld += PendingBgWriterStats.fld

  BGWRITER_ACC(buf_written_clean);

  BGWRITER_ACC(maxwritten_clean);

  BGWRITER_ACC(buf_alloc);

#undef BGWRITER_ACC

  pgstat_end_changecount_write(&stats_shmem->changecount);

  /*

   * Clear out the statistics buffer, so it can be re-used.

   */

  MemSet(&PendingBgWriterStats, 0, sizeof(PendingBgWriterStats));

  /*

   * Report IO statistics

   */

  pgstat_flush_io(false);

}

/*

 * Support function for the SQL-callable pgstat* functions. Returns

 * a pointer to the bgwriter statistics struct.

 */

PgStat_BgWriterStats *

pgstat_fetch_stat_bgwriter(void)

{

  pgstat_snapshot_fixed(PGSTAT_KIND_BGWRITER);

  return &pgStatLocal.snapshot.bgwriter;

}

void

pgstat_bgwriter_init_shmem_cb(void *stats)

{

  PgStatShared_BgWriter *stats_shmem = (PgStatShared_BgWriter *) stats;

  LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);

}

void

pgstat_bgwriter_reset_all_cb(TimestampTz ts)

{

  PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;

  /* see explanation above PgStatShared_BgWriter for the reset protocol */

  LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);

  pgstat_copy_changecounted_stats(&stats_shmem->reset_offset,

                  &stats_shmem->stats,

                  sizeof(stats_shmem->stats),

                  &stats_shmem->changecount);

  stats_shmem->stats.stat_reset_timestamp = ts;

  LWLockRelease(&stats_shmem->lock);

}

void

pgstat_bgwriter_snapshot_cb(void)

{

  PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;

  PgStat_BgWriterStats *reset_offset = &stats_shmem->reset_offset;

  PgStat_BgWriterStats reset;

  pgstat_copy_changecounted_stats(&pgStatLocal.snapshot.bgwriter,

                  &stats_shmem->stats,

                  sizeof(stats_shmem->stats),

                  &stats_shmem->changecount);

  LWLockAcquire(&stats_shmem->lock, LW_SHARED);

  memcpy(&reset, reset_offset, sizeof(stats_shmem->stats));

  LWLockRelease(&stats_shmem->lock);

  /* compensate by reset offsets */

#define BGWRITER_COMP(fld) pgStatLocal.snapshot.bgwriter.fld -= reset.fld;

  BGWRITER_COMP(buf_written_clean);

  BGWRITER_COMP(maxwritten_clean);

  BGWRITER_COMP(buf_alloc);

#undef BGWRITER_COMP

}