From 88bdbd3f746049834ae3cc972e6e650586ec3c9d Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Thu, 29 Nov 2018 18:42:53 -0300 Subject: Add log_statement_sample_rate parameter This allows to set a lower log_min_duration_statement value without incurring excessive log traffic (which reduces performance). This can be useful to analyze workloads with lots of short queries. Author: Adrien Nayrat Reviewed-by: David Rowley, Vik Fearing Discussion: https://postgr.es/m/c30ee535-ee1e-db9f-fa97-146b9f62caed@anayrat.info --- src/backend/tcop/postgres.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'src/backend/tcop/postgres.c') diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index a3b9757565e..9a948f825df 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -2201,7 +2201,8 @@ check_log_statement(List *stmt_list) /* * check_log_duration - * Determine whether current command's duration should be logged + * Determine whether current command's duration should be logged. + * If log_statement_sample_rate < 1.0, log only a sample. * * Returns: * 0 if no logging is needed @@ -2223,6 +2224,7 @@ check_log_duration(char *msec_str, bool was_logged) int usecs; int msecs; bool exceeded; + bool in_sample; TimestampDifference(GetCurrentStatementStartTimestamp(), GetCurrentTimestamp(), @@ -2239,7 +2241,17 @@ check_log_duration(char *msec_str, bool was_logged) (secs > log_min_duration_statement / 1000 || secs * 1000 + msecs >= log_min_duration_statement))); - if (exceeded || log_duration) + /* + * 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) + in_sample = log_statement_sample_rate != 0 && + (log_statement_sample_rate == 1 || + random() <= log_statement_sample_rate * MAX_RANDOM_VALUE); + + if ((exceeded && in_sample) || log_duration) { snprintf(msec_str, 32, "%ld.%03d", secs * 1000 + msecs, usecs % 1000); -- cgit v1.2.3