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Revert "Add log_statement_sample_rate parameter"

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This reverts commit 88bdbd3f74.

As committed, statement sampling used the existing duration threshold
(log_min_duration_statement) when decide which statements to sample.
The issue is that even the longest statements are subject to sampling,
and so may not end up logged. An improvement was proposed, introducing
a second duration threshold, but it would not be backwards compatible.
So we've decided to revert this feature - the separate threshold should
be part of the feature itself.

Discussion: https://postgr.es/m/CAFj8pRDS8tQ3Wviw9%3DAvODyUciPSrGeMhJi_WPE%2BEB8%2B4gLL-Q%40mail.gmail.com
This commit is contained in:
Tomas Vondra
2019-08-04 20:29:00 +02:00
parent 4f9ed8f3c5
commit 75506195da
5 changed files with 13 additions and 65 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
src/backend/tcop/postgres.c
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@ -2212,8 +2212,7 @@ check_log_statement(List *stmt_list)
/*
* check_log_duration
* Determine whether current command's duration should be logged.
* If log_statement_sample_rate < 1.0, log only a sample.
* Determine whether current command's duration should be logged
* We also check if this statement in this transaction must be logged
* (regardless of its duration).
*
@ -2237,7 +2236,6 @@ check_log_duration(char *msec_str, bool was_logged)
int usecs;
int msecs;
bool exceeded;
bool in_sample;
TimestampDifference(GetCurrentStatementStartTimestamp(),
GetCurrentTimestamp(),
@ -2254,17 +2252,7 @@ check_log_duration(char *msec_str, bool was_logged)
(secs > log_min_duration_statement / 1000 ||
secs * 1000 + msecs >= log_min_duration_statement)));
/*
* 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 || xact_is_sampled)
if (exceeded || log_duration || xact_is_sampled)
{
snprintf(msec_str, 32, "%ld.%03d",
secs * 1000 + msecs, usecs % 1000);

15
src/backend/utils/misc/guc.c
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@ -511,7 +511,6 @@ int log_min_messages = WARNING;
int client_min_messages = NOTICE;
int log_min_duration_statement = -1;
int log_temp_files = -1;
double log_statement_sample_rate = 1.0;
double log_xact_sample_rate = 0;
int trace_recovery_messages = LOG;
@ -2705,8 +2704,7 @@ static struct config_int ConfigureNamesInt[] =
{"log_min_duration_statement", PGC_SUSET, LOGGING_WHEN,
gettext_noop("Sets the minimum execution time above which "
"statements will be logged."),
gettext_noop("Zero prints all queries, subject to log_statement_sample_rate. "
"-1 turns this feature off."),
gettext_noop("Zero prints all queries. -1 turns this feature off."),
GUC_UNIT_MS
},
&log_min_duration_statement,
@ -3432,17 +3430,6 @@ static struct config_real ConfigureNamesReal[] =
NULL, NULL, NULL
},
{
{"log_statement_sample_rate", PGC_SUSET, LOGGING_WHEN,
gettext_noop("Fraction of statements exceeding log_min_duration_statement to be logged."),
gettext_noop("If you only want a sample, use a value between 0.0 (never "
"log) and 1.0 (always log).")
},
&log_statement_sample_rate,
1.0, 0.0, 1.0,
NULL, NULL, NULL
},
{
{"log_transaction_sample_rate", PGC_SUSET, LOGGING_WHEN,
gettext_noop("Set the fraction of transactions to log for new transactions."),

12
src/backend/utils/misc/postgresql.conf.sample
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@ -488,14 +488,10 @@
# fatal
# panic (effectively off)
#log_min_duration_statement = -1 # logs statements and their durations
# according to log_statement_sample_rate. -1 is disabled,
# 0 logs all statements, > 0 logs only statements running
# at least this number of milliseconds.
#log_statement_sample_rate = 1.0 # Fraction of logged statements exceeding
# log_min_duration_statement to be logged.
# 1.0 logs all such statements, 0.0 never logs.
#log_min_duration_statement = -1 # -1 is disabled, 0 logs all statements
# and their durations, > 0 logs only
# statements running at least this number
# of milliseconds
#log_transaction_sample_rate = 0.0 # Fraction of transactions whose statements
# are logged regardless of their duration. 1.0 logs all

1
src/include/utils/guc.h
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@ -253,7 +253,6 @@ extern PGDLLIMPORT int log_min_messages;
extern PGDLLIMPORT int client_min_messages;
extern int log_min_duration_statement;
extern int log_temp_files;
extern double log_statement_sample_rate;
extern double log_xact_sample_rate;
extern int temp_file_limit;