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pg_stat_wal: Accumulate time as instr_time instead of microseconds
In instr_time.h it is stated that: * When summing multiple measurements, it's recommended to leave the * running sum in instr_time form (ie, use INSTR_TIME_ADD or * INSTR_TIME_ACCUM_DIFF) and convert to a result format only at the end. The reason for that is that converting to microseconds is not cheap, and can loose precision. Therefore this commit changes 'PendingWalStats' to use 'instr_time' instead of 'PgStat_Counter' while accumulating 'wal_write_time' and 'wal_sync_time'. Author: Nazir Bilal Yavuz <byavuz81@gmail.com> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> Reviewed-by: Melanie Plageman <melanieplageman@gmail.com> Discussion: https://postgr.es/m/1feedb83-7aa9-cb4b-5086-598349d3f555@gmail.com
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@ -2206,8 +2206,7 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
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instr_time duration;
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instr_time duration;
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INSTR_TIME_SET_CURRENT(duration);
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INSTR_TIME_SET_CURRENT(duration);
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INSTR_TIME_SUBTRACT(duration, start);
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INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_write_time, duration, start);
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PendingWalStats.wal_write_time += INSTR_TIME_GET_MICROSEC(duration);
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}
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}
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PendingWalStats.wal_write++;
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PendingWalStats.wal_write++;
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@ -8204,8 +8203,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
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instr_time duration;
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instr_time duration;
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INSTR_TIME_SET_CURRENT(duration);
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INSTR_TIME_SET_CURRENT(duration);
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INSTR_TIME_SUBTRACT(duration, start);
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INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_sync_time, duration, start);
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PendingWalStats.wal_sync_time += INSTR_TIME_GET_MICROSEC(duration);
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}
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}
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PendingWalStats.wal_sync++;
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PendingWalStats.wal_sync++;
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@ -469,8 +469,7 @@ BufFileLoadBuffer(BufFile *file)
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if (track_io_timing)
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if (track_io_timing)
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{
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{
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INSTR_TIME_SET_CURRENT(io_time);
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INSTR_TIME_SET_CURRENT(io_time);
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INSTR_TIME_SUBTRACT(io_time, io_start);
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INSTR_TIME_ACCUM_DIFF(pgBufferUsage.temp_blk_read_time, io_time, io_start);
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INSTR_TIME_ADD(pgBufferUsage.temp_blk_read_time, io_time);
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}
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}
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/* we choose not to advance curOffset here */
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/* we choose not to advance curOffset here */
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@ -544,8 +543,7 @@ BufFileDumpBuffer(BufFile *file)
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if (track_io_timing)
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if (track_io_timing)
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{
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{
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INSTR_TIME_SET_CURRENT(io_time);
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INSTR_TIME_SET_CURRENT(io_time);
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INSTR_TIME_SUBTRACT(io_time, io_start);
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INSTR_TIME_ACCUM_DIFF(pgBufferUsage.temp_blk_write_time, io_time, io_start);
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INSTR_TIME_ADD(pgBufferUsage.temp_blk_write_time, io_time);
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}
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}
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file->curOffset += bytestowrite;
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file->curOffset += bytestowrite;
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@ -21,7 +21,7 @@
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#include "executor/instrument.h"
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#include "executor/instrument.h"
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PgStat_WalStats PendingWalStats = {0};
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PgStat_PendingWalStats PendingWalStats = {0};
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/*
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/*
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* WAL usage counters saved from pgWALUsage at the previous call to
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* WAL usage counters saved from pgWALUsage at the previous call to
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@ -70,7 +70,7 @@ bool
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pgstat_flush_wal(bool nowait)
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pgstat_flush_wal(bool nowait)
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{
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{
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PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
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PgStatShared_Wal *stats_shmem = &pgStatLocal.shmem->wal;
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WalUsage diff = {0};
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WalUsage wal_usage_diff = {0};
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Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
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Assert(IsUnderPostmaster || !IsPostmasterEnvironment);
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Assert(pgStatLocal.shmem != NULL &&
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Assert(pgStatLocal.shmem != NULL &&
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@ -88,25 +88,26 @@ pgstat_flush_wal(bool nowait)
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* Calculate how much WAL usage counters were increased by subtracting the
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* Calculate how much WAL usage counters were increased by subtracting the
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* previous counters from the current ones.
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* previous counters from the current ones.
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*/
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*/
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WalUsageAccumDiff(&diff, &pgWalUsage, &prevWalUsage);
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WalUsageAccumDiff(&wal_usage_diff, &pgWalUsage, &prevWalUsage);
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PendingWalStats.wal_records = diff.wal_records;
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PendingWalStats.wal_fpi = diff.wal_fpi;
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PendingWalStats.wal_bytes = diff.wal_bytes;
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if (!nowait)
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if (!nowait)
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LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
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LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
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else if (!LWLockConditionalAcquire(&stats_shmem->lock, LW_EXCLUSIVE))
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else if (!LWLockConditionalAcquire(&stats_shmem->lock, LW_EXCLUSIVE))
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return true;
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return true;
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#define WALSTAT_ACC(fld) stats_shmem->stats.fld += PendingWalStats.fld
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#define WALSTAT_ACC(fld, var_to_add) \
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WALSTAT_ACC(wal_records);
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(stats_shmem->stats.fld += var_to_add.fld)
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WALSTAT_ACC(wal_fpi);
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#define WALSTAT_ACC_INSTR_TIME(fld) \
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WALSTAT_ACC(wal_bytes);
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(stats_shmem->stats.fld += INSTR_TIME_GET_MICROSEC(PendingWalStats.fld))
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WALSTAT_ACC(wal_buffers_full);
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WALSTAT_ACC(wal_records, wal_usage_diff);
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WALSTAT_ACC(wal_write);
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WALSTAT_ACC(wal_fpi, wal_usage_diff);
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WALSTAT_ACC(wal_sync);
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WALSTAT_ACC(wal_bytes, wal_usage_diff);
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WALSTAT_ACC(wal_write_time);
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WALSTAT_ACC(wal_buffers_full, PendingWalStats);
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WALSTAT_ACC(wal_sync_time);
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WALSTAT_ACC(wal_write, PendingWalStats);
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WALSTAT_ACC(wal_sync, PendingWalStats);
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WALSTAT_ACC_INSTR_TIME(wal_write_time);
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WALSTAT_ACC_INSTR_TIME(wal_sync_time);
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#undef WALSTAT_ACC_INSTR_TIME
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#undef WALSTAT_ACC
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#undef WALSTAT_ACC
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LWLockRelease(&stats_shmem->lock);
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LWLockRelease(&stats_shmem->lock);
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@ -435,6 +435,21 @@ typedef struct PgStat_WalStats
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TimestampTz stat_reset_timestamp;
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TimestampTz stat_reset_timestamp;
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} PgStat_WalStats;
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} PgStat_WalStats;
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/*
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* This struct stores wal-related durations as instr_time, which makes it
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* cheaper and easier to accumulate them, by not requiring type
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* conversions. During stats flush instr_time will be converted into
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* microseconds.
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*/
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typedef struct PgStat_PendingWalStats
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{
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PgStat_Counter wal_buffers_full;
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PgStat_Counter wal_write;
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PgStat_Counter wal_sync;
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instr_time wal_write_time;
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instr_time wal_sync_time;
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} PgStat_PendingWalStats;
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/*
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/*
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* Functions in pgstat.c
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* Functions in pgstat.c
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@ -748,7 +763,7 @@ extern PGDLLIMPORT SessionEndType pgStatSessionEndCause;
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*/
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*/
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/* updated directly by backends and background processes */
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/* updated directly by backends and background processes */
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extern PGDLLIMPORT PgStat_WalStats PendingWalStats;
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extern PGDLLIMPORT PgStat_PendingWalStats PendingWalStats;
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#endif /* PGSTAT_H */
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#endif /* PGSTAT_H */
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@ -2053,6 +2053,7 @@ PgStat_Kind
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PgStat_KindInfo
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PgStat_KindInfo
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PgStat_LocalState
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PgStat_LocalState
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PgStat_PendingDroppedStatsItem
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PgStat_PendingDroppedStatsItem
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PgStat_PendingWalStats
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PgStat_SLRUStats
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PgStat_SLRUStats
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PgStat_ShmemControl
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PgStat_ShmemControl
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PgStat_Snapshot
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PgStat_Snapshot
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