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Commit4766438

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Adjust some comments about structure properties in pg_stat.h
One comment of PgStat_TableCounts mentioned that its pending stats usememcmp() to check for the all-zero case if there is any activity. Thisis not true since07e9e28, 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 functionstatistics 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() (since07e9e28 for the latter), and nevermentioned the dependency on event counters for their all-zero checks.Let's document these properties, like the table statistics.Author: Bertrand DrouvotDiscussion:https://postgr.es/m/Z1hNLvcPgVLPxCoc@ip-10-97-1-34.eu-west-3.compute.internal
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‎src/include/pgstat.h

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Original file line numberDiff line numberDiff line change
@@ -128,9 +128,6 @@ typedef int64 PgStat_Counter;
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/* ----------
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* PgStat_FunctionCountsThe actual per-function counts kept by a backend
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*
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* This struct should contain only actual event counters, because we memcmp
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* it against zeroes to detect whether there are any pending stats.
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*
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* Note that the time counters are in instr_time format here. We convert to
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* microseconds in PgStat_Counter format when flushing out pending statistics.
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* ----------
@@ -172,8 +169,10 @@ typedef struct PgStat_BackendSubEntry
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/* ----------
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* PgStat_TableCountsThe actual per-table counts kept by a backend
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*
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* This struct should contain only actual event counters, because we memcmp
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* it against zeroes to detect whether there are any stats updates to apply.
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* This struct should contain only actual event counters, because we make use
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* of pg_memory_is_all_zeros() to detect whether there are any stats updates
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* to apply.
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*
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* It is a component of PgStat_TableStatus (within-backend state).
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*
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* Note: for a table, tuples_returned is the number of tuples successfully
@@ -282,6 +281,14 @@ typedef struct PgStat_ArchiverStats
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TimestampTzstat_reset_timestamp;
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}PgStat_ArchiverStats;
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/* ---------
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* PgStat_BgWriterStatsBackground Writer statistics
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*
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* This struct should contain only actual event counters, because we make use
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* of pg_memory_is_all_zeros() to detect whether there are any stats updates
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* to apply.
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* ---------
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*/
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typedefstructPgStat_BgWriterStats
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{
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PgStat_Counterbuf_written_clean;
@@ -290,6 +297,14 @@ typedef struct PgStat_BgWriterStats
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TimestampTzstat_reset_timestamp;
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}PgStat_BgWriterStats;
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/* --------
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* PgStat_CheckpointerStatsCheckpoint statistics
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*
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* This struct should contain only actual event counters, because we make use
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* of pg_memory_is_all_zeros() to detect whether there are any stats updates to
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* apply.
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* ---------
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*/
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typedefstructPgStat_CheckpointerStats
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{
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PgStat_Counternum_timed;

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