Hello, Per idea of Nikolay Samokhvalov[1] I propose this patch to add the possibility to log all statements from a fraction of transactions.
I have several questions: * Do we want this feature? * How can I add tests? I seems hard to handle tests when a there is duration in the output. * Should I handle the case when someone try to change the setting *inside* a transaction: # SET client_min_messages to LOG; SET # SET log_transaction_sample_rate to 1; SET # BEGIN; LOG: duration: 0.364 ms statement: BEGIN; BEGIN # SELECT 1; LOG: duration: 0.530 ms statement: SELECT 1; -[ RECORD 1 ] ?column? | 1 # SET log_transaction_sample_rate to 0; LOG: duration: 0.333 ms statement: SET log_transaction_sample_rate to 0; SET # SELECT 1; LOG: duration: 0.586 ms statement: SELECT 1; -[ RECORD 1 ] ?column? | 1 Thanks [1]: https://www.postgresql.org/message-id/CANNMO%2BLg65EFqHb%2BZYbMLKyE2y498HJzsdFrMnW1dQ6AFJ3Mpw%40mail.gmail.com -- Adrien NAYRAT
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 4a7121a51f..7312b1022f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5771,6 +5771,24 @@ local0.* /var/log/postgresql
</listitem>
</varlistentry>
+ <varlistentry id="guc-transaction-sample-rate" xreflabel="log_transaction_sample_rate">
+ <term><varname>log_transaction_sample_rate</varname> (<type>real</type>)
+ <indexterm>
+ <primary><varname>log_transaction_sample_rate</varname> configuration parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Set the fraction of transactions whose statements are logged. It applies
+ to each new transaction regardless of their duration. The default is
+ <literal>0</literal>, meaning do not log statements from this transaction.
+ Setting this to <literal>1</literal> logs all statements for all transactions.
+ <varname>log_transaction_sample_rate</varname> is helpful to track a
+ sample of transaction.
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
<para>
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index d967400384..d622023ebe 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -75,6 +75,7 @@ int XactIsoLevel;
bool DefaultXactReadOnly = false;
bool XactReadOnly;
+bool xact_is_sampled;
bool DefaultXactDeferrable = false;
bool XactDeferrable;
@@ -1821,6 +1822,9 @@ StartTransaction(void)
s->state = TRANS_START;
s->transactionId = InvalidTransactionId; /* until assigned */
+ /* Determine if we log statements in this transaction */
+ xact_is_sampled = random() <= log_xact_sample_rate * MAX_RANDOM_VALUE;
+
/*
* initialize current transaction state fields
*
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 5ab7d3cd8d..8f1ae0a5dd 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -100,7 +100,8 @@ int max_stack_depth = 100;
/* wait N seconds to allow attach from a debugger */
int PostAuthDelay = 0;
-
+/* flag for logging statements in this transaction */
+bool xact_is_sampled = false;
/* ----------------
* private variables
@@ -2203,6 +2204,8 @@ 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.
+ * We also check if this statement in this transaction must be logged
+ * (regardless of its duration).
*
* Returns:
* 0 if no logging is needed
@@ -2218,7 +2221,7 @@ check_log_statement(List *stmt_list)
int
check_log_duration(char *msec_str, bool was_logged)
{
- if (log_duration || log_min_duration_statement >= 0)
+ if (log_duration || log_min_duration_statement >= 0 || xact_is_sampled)
{
long secs;
int usecs;
@@ -2252,11 +2255,11 @@ check_log_duration(char *msec_str, bool was_logged)
(log_statement_sample_rate == 1 ||
random() <= log_statement_sample_rate * MAX_RANDOM_VALUE);
- if ((exceeded && in_sample) || log_duration)
+ if ((exceeded && in_sample) || log_duration || xact_is_sampled)
{
snprintf(msec_str, 32, "%ld.%03d",
secs * 1000 + msecs, usecs % 1000);
- if (exceeded && !was_logged)
+ if ((exceeded || xact_is_sampled) && !was_logged)
return 2;
else
return 1;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6fe1939881..160c725123 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -487,6 +487,7 @@ 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;
int temp_file_limit = -1;
@@ -3325,13 +3326,25 @@ static struct config_real ConfigureNamesReal[] =
{"log_statement_sample_rate", PGC_SUSET, LOGGING_WHEN,
gettext_noop("Fraction of statements over log_min_duration_statement to log."),
gettext_noop("If you only want a sample, use a value between 0 (never "
- "log) and 1.0 (always log).")
+ "log) and 1 (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."),
+ gettext_noop("Logs all statements from a fraction of transactions. "
+ "Use a value between 0 (never log) and 1 (log all "
+ "statements for all transactions).")
+ },
+ &log_xact_sample_rate,
+ 0.0, 0.0, 1.0,
+ NULL, NULL, NULL
+ },
+
/* End-of-list marker */
{
{NULL, 0, 0, NULL, NULL}, NULL, 0.0, 0.0, 0.0, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 1fa02d2c93..89553f5302 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -492,6 +492,10 @@
# log_min_duration_statement. 1.0 logs all statements,
# 0 never logs.
+#log_transaction_sample_rate = 0 # Fraction of transactions whose statements
+ # are logged regardless of their duration. 1.0 logs all
+ # statements from all transactions, 0 never logs.
+
# - What to Log -
#debug_print_parse = off
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index 689c57c592..70759b63a0 100644
--- a/src/include/access/xact.h
+++ b/src/include/access/xact.h
@@ -54,6 +54,9 @@ extern PGDLLIMPORT int XactIsoLevel;
extern bool DefaultXactReadOnly;
extern bool XactReadOnly;
+/* flag for logging statements in this transaction */
+extern bool xact_is_sampled;
+
/*
* Xact is deferrable -- only meaningful (currently) for read only
* SERIALIZABLE transactions
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 64457c792a..e7325fbdb7 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -252,6 +252,7 @@ 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;
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