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author | Tomas Vondra <tomas.vondra@postgresql.org> | 2019-11-04 01:57:45 +0100 |
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committer | Tomas Vondra <tomas.vondra@postgresql.org> | 2019-11-06 19:11:07 +0100 |
commit | 6e3e6cc0e884a6091e1094dff29db430af08fb93 (patch) | |
tree | b44e1702678389fc68ec9a2da2ff5bb21c4db9a5 /src/backend/tcop/postgres.c | |
parent | 11d9ac28e5e0077d8f23761c2962a30423f44cee (diff) | |
download | postgresql-6e3e6cc0e884a6091e1094dff29db430af08fb93.tar.gz postgresql-6e3e6cc0e884a6091e1094dff29db430af08fb93.zip |
Allow sampling of statements depending on duration
This allows logging a sample of statements, without incurring excessive
log traffic (which may impact performance). This can be useful when
analyzing workloads with lots of short queries.
The sampling is configured using two new GUC parameters:
* log_min_duration_sample - minimum required statement duration
* log_statement_sample_rate - sample rate (0.0 - 1.0)
Only statements with duration exceeding log_min_duration_sample are
considered for sampling. To enable sampling, both those GUCs have to
be set correctly.
The existing log_min_duration_statement GUC has a higher priority, i.e.
statements with duration exceeding log_min_duration_statement will be
always logged, irrespectedly of how the sampling is configured. This
means only configurations
log_min_duration_sample < log_min_duration_statement
do actually sample the statements, instead of logging everything.
Author: Adrien Nayrat
Reviewed-by: David Rowley, Vik Fearing, Tomas Vondra
Discussion: https://postgr.es/m/bbe0a1a8-a8f7-3be2-155a-888e661cc06c@anayrat.info
Diffstat (limited to 'src/backend/tcop/postgres.c')
-rw-r--r-- | src/backend/tcop/postgres.c | 40 |
1 files changed, 29 insertions, 11 deletions
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index 4bec40aa287..82894eadc66 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -2235,12 +2235,15 @@ check_log_statement(List *stmt_list) int check_log_duration(char *msec_str, bool was_logged) { - if (log_duration || log_min_duration_statement >= 0 || xact_is_sampled) + if (log_duration || log_min_duration_sample >= 0 || + log_min_duration_statement >= 0 || xact_is_sampled) { long secs; int usecs; int msecs; - bool exceeded; + bool exceeded_duration; + bool exceeded_sample_duration; + bool in_sample = false; TimestampDifference(GetCurrentStatementStartTimestamp(), GetCurrentTimestamp(), @@ -2248,20 +2251,35 @@ check_log_duration(char *msec_str, bool was_logged) msecs = usecs / 1000; /* - * This odd-looking test for log_min_duration_statement being exceeded - * is designed to avoid integer overflow with very long durations: - * don't compute secs * 1000 until we've verified it will fit in int. + * This odd-looking test for log_min_duration_* being exceeded is + * designed to avoid integer overflow with very long durations: don't + * compute secs * 1000 until we've verified it will fit in int. */ - exceeded = (log_min_duration_statement == 0 || - (log_min_duration_statement > 0 && - (secs > log_min_duration_statement / 1000 || - secs * 1000 + msecs >= log_min_duration_statement))); + exceeded_duration = (log_min_duration_statement == 0 || + (log_min_duration_statement > 0 && + (secs > log_min_duration_statement / 1000 || + secs * 1000 + msecs >= log_min_duration_statement))); - if (exceeded || log_duration || xact_is_sampled) + exceeded_sample_duration = (log_min_duration_sample == 0 || + (log_min_duration_sample > 0 && + (secs > log_min_duration_sample / 1000 || + secs * 1000 + msecs >= log_min_duration_sample))); + + /* + * Do not log if log_statement_sample_rate = 0. Log a sample if + * log_statement_sample_rate <= 1 and avoid unecessary random() call + * if log_statement_sample_rate = 1. + */ + if (exceeded_sample_duration) + in_sample = log_statement_sample_rate != 0 && + (log_statement_sample_rate == 1 || + random() <= log_statement_sample_rate * MAX_RANDOM_VALUE); + + if (exceeded_duration || in_sample || log_duration || xact_is_sampled) { snprintf(msec_str, 32, "%ld.%03d", secs * 1000 + msecs, usecs % 1000); - if ((exceeded || xact_is_sampled) && !was_logged) + if ((exceeded_duration || in_sample || xact_is_sampled) && !was_logged) return 2; else return 1; |