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| author | Michael Paquier <michael@paquier.xyz> | 2024-12-12 16:59:22 +0900 |
|---|---|---|
| committer | Michael Paquier <michael@paquier.xyz> | 2024-12-12 16:59:22 +0900 |
| commit | 4766438aa317e85f3d762847b2b009f91f530b6f (patch) | |
| tree | 688e86595178f1fccf72c96cfc7a677a484f2b6c /src | |
| parent | bd10ec529796a13670645e6acd640c6f290df020 (diff) | |
| download | postgresql-4766438aa317e85f3d762847b2b009f91f530b6f.tar.gz postgresql-4766438aa317e85f3d762847b2b009f91f530b6f.zip | |
Adjust some comments about structure properties in pg_stat.h
One comment of PgStat_TableCounts mentioned that its pending stats use
memcmp() to check for the all-zero case if there is any activity. This
is not true since 07e9e28b56, as pg_memory_is_all_zeros() is used.
PgStat_FunctionCounts incorrectly documented that it relied on memcpy().
This has never been correct, and not relevant because function
statistics do not have an all-zero check for pending stats.
Checkpoint and bgwriter statistics have been always relying on memcmp()
or pg_memory_is_all_zeros() (since 07e9e28b56 for the latter), and never
mentioned the dependency on event counters for their all-zero checks.
Let's document these properties, like the table statistics.
Author: Bertrand Drouvot
Discussion: https://postgr.es/m/Z1hNLvcPgVLPxCoc@ip-10-97-1-34.eu-west-3.compute.internal
Diffstat (limited to 'src')
| -rw-r--r-- | src/include/pgstat.h | 25 |
1 files changed, 20 insertions, 5 deletions
diff --git a/src/include/pgstat.h b/src/include/pgstat.h index 59c28b4aca8..ebfeef2f460 100644 --- a/src/include/pgstat.h +++ b/src/include/pgstat.h @@ -128,9 +128,6 @@ typedef int64 PgStat_Counter; /* ---------- * PgStat_FunctionCounts The actual per-function counts kept by a backend * - * This struct should contain only actual event counters, because we memcmp - * it against zeroes to detect whether there are any pending stats. - * * Note that the time counters are in instr_time format here. We convert to * microseconds in PgStat_Counter format when flushing out pending statistics. * ---------- @@ -172,8 +169,10 @@ typedef struct PgStat_BackendSubEntry /* ---------- * PgStat_TableCounts The actual per-table counts kept by a backend * - * This struct should contain only actual event counters, because we memcmp - * it against zeroes to detect whether there are any stats updates to apply. + * This struct should contain only actual event counters, because we make use + * of pg_memory_is_all_zeros() to detect whether there are any stats updates + * to apply. + * * It is a component of PgStat_TableStatus (within-backend state). * * Note: for a table, tuples_returned is the number of tuples successfully @@ -282,6 +281,14 @@ typedef struct PgStat_ArchiverStats TimestampTz stat_reset_timestamp; } PgStat_ArchiverStats; +/* --------- + * PgStat_BgWriterStats Background Writer statistics + * + * This struct should contain only actual event counters, because we make use + * of pg_memory_is_all_zeros() to detect whether there are any stats updates + * to apply. + * --------- + */ typedef struct PgStat_BgWriterStats { PgStat_Counter buf_written_clean; @@ -290,6 +297,14 @@ typedef struct PgStat_BgWriterStats TimestampTz stat_reset_timestamp; } PgStat_BgWriterStats; +/* -------- + * PgStat_CheckpointerStats Checkpoint statistics + * + * This struct should contain only actual event counters, because we make use + * of pg_memory_is_all_zeros() to detect whether there are any stats updates to + * apply. + * --------- + */ typedef struct PgStat_CheckpointerStats { PgStat_Counter num_timed; |