PostgreSQL Source Code: src/backend/utils/activity/pgstat_bgwriter.c Source File

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pgstat_bgwriter.c
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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 */
30void
31 pgstat_report_bgwriter(void)
32{
33 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 if (pg_memory_is_all_zeros(&PendingBgWriterStats,
43 sizeof(struct PgStat_BgWriterStats)))
44 return;
45
46 pgstat_begin_changecount_write(&stats_shmem->changecount);
47
48#define BGWRITER_ACC(fld) stats_shmem->stats.fld += PendingBgWriterStats.fld
49 BGWRITER_ACC(buf_written_clean);
50 BGWRITER_ACC(maxwritten_clean);
51 BGWRITER_ACC(buf_alloc);
52#undef BGWRITER_ACC
53
54 pgstat_end_changecount_write(&stats_shmem->changecount);
55
56 /*
57 * Clear out the statistics buffer, so it can be re-used.
58 */
59 MemSet(&PendingBgWriterStats, 0, sizeof(PendingBgWriterStats));
60
61 /*
62 * Report IO statistics
63 */
64 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 */
71PgStat_BgWriterStats *
72 pgstat_fetch_stat_bgwriter(void)
73{
74 pgstat_snapshot_fixed(PGSTAT_KIND_BGWRITER);
75
76 return &pgStatLocal.snapshot.bgwriter;
77}
78
79void
80 pgstat_bgwriter_init_shmem_cb(void *stats)
81{
82 PgStatShared_BgWriter *stats_shmem = (PgStatShared_BgWriter *) stats;
83
84 LWLockInitialize(&stats_shmem->lock, LWTRANCHE_PGSTATS_DATA);
85}
86
87void
88 pgstat_bgwriter_reset_all_cb(TimestampTz ts)
89{
90 PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
91
92 /* see explanation above PgStatShared_BgWriter for the reset protocol */
93 LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
94 pgstat_copy_changecounted_stats(&stats_shmem->reset_offset,
95 &stats_shmem->stats,
96 sizeof(stats_shmem->stats),
97 &stats_shmem->changecount);
98 stats_shmem->stats.stat_reset_timestamp = ts;
99 LWLockRelease(&stats_shmem->lock);
100}
101
102void
103 pgstat_bgwriter_snapshot_cb(void)
104{
105 PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
106 PgStat_BgWriterStats *reset_offset = &stats_shmem->reset_offset;
107 PgStat_BgWriterStats reset;
108
109 pgstat_copy_changecounted_stats(&pgStatLocal.snapshot.bgwriter,
110 &stats_shmem->stats,
111 sizeof(stats_shmem->stats),
112 &stats_shmem->changecount);
113
114 LWLockAcquire(&stats_shmem->lock, LW_SHARED);
115 memcpy(&reset, reset_offset, sizeof(stats_shmem->stats));
116 LWLockRelease(&stats_shmem->lock);
117
118 /* compensate by reset offsets */
119#define BGWRITER_COMP(fld) pgStatLocal.snapshot.bgwriter.fld -= reset.fld;
120 BGWRITER_COMP(buf_written_clean);
121 BGWRITER_COMP(maxwritten_clean);
122 BGWRITER_COMP(buf_alloc);
123#undef BGWRITER_COMP
124}
#define MemSet(start, val, len)
Definition: c.h:1019
int64 TimestampTz
Definition: timestamp.h:39
Assert(PointerIsAligned(start, uint64))
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1174
void LWLockRelease(LWLock *lock)
Definition: lwlock.c:1894
void LWLockInitialize(LWLock *lock, int tranche_id)
Definition: lwlock.c:698
@ LW_SHARED
Definition: lwlock.h:113
@ LW_EXCLUSIVE
Definition: lwlock.h:112
static bool pg_memory_is_all_zeros(const void *ptr, size_t len)
Definition: memutils.h:219
void pgstat_snapshot_fixed(PgStat_Kind kind)
Definition: pgstat.c:1058
PgStat_LocalState pgStatLocal
Definition: pgstat.c:212
#define BGWRITER_ACC(fld)
PgStat_BgWriterStats PendingBgWriterStats
void pgstat_bgwriter_reset_all_cb(TimestampTz ts)
#define BGWRITER_COMP(fld)
PgStat_BgWriterStats * pgstat_fetch_stat_bgwriter(void)
void pgstat_bgwriter_init_shmem_cb(void *stats)
void pgstat_bgwriter_snapshot_cb(void)
void pgstat_report_bgwriter(void)
static void pgstat_end_changecount_write(uint32 *cc)
#define pgstat_assert_is_up()
static void pgstat_begin_changecount_write(uint32 *cc)
static void pgstat_copy_changecounted_stats(void *dst, void *src, size_t len, uint32 *cc)
void pgstat_flush_io(bool nowait)
Definition: pgstat_io.c:175
#define PGSTAT_KIND_BGWRITER
Definition: pgstat_kind.h:36
void reset(void)
Definition: sql-declare.c:600
PgStat_BgWriterStats reset_offset
uint32 changecount
PgStat_BgWriterStats stats
LWLock lock
Definition: pgstat.h:239
TimestampTz stat_reset_timestamp
Definition: pgstat.h:243
PgStat_Snapshot snapshot
PgStat_ShmemControl * shmem
bool is_shutdown
PgStatShared_BgWriter bgwriter
PgStat_BgWriterStats bgwriter

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