On 3/28/19 10:45 AM, Christoph Berg wrote:
Re: Adrien NAYRAT 2019-03-28 <c86d676a-0b1e-f9be-3da2-63fa15070...@anayrat.info>
Sorry, I changed that, someone suggest using either "0" and "1", or
"0.0" and "1.0" but not mixing both.
Agreed with using "0.0" and "1.0".
I will remove this change.
+#log_transaction_sample_rate = 0 # Fraction of transactions whose
statements
+ # are logged regardless of their
duration. 1.0 logs all
+ # statements from all transactions, 0.0
never logs.
This still looks weird to me. If the default is to never log, and
that's 0.0 as per the comment, the setting should be 0.0 as well.
Right, fixed in patch attached
The same applies to log_statement_sample_rate which is already
committed, were it looks even worse:
Yes, I fixed in this patch, but, as it is not related to this patch, it
should be fixed in another patch.
#log_statement_sample_rate = 1 # Fraction of logged statements over
# log_min_duration_statement. 1.0 logs
all statements,
# 0 never logs.
Is "over" even correct English? ("out of" "from"?)
I have no idea on it, I am not an English native speaker.
Thanks,
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d383de2512..99e38b32d1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5836,6 +5836,31 @@ 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>
+ <note>
+ <para>
+ This option can add overhead when transactions are large (many short queries).
+ Or, when the workload is high and <varname>log_transaction_sample_rate</varname>
+ is closed to 1.
+ </para>
+ </note>
+ </listitem>
+ </varlistentry>
+
</variablelist>
<para>
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index c3214d4f4d..9fb9658a12 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -245,6 +245,9 @@ static char *prepareGID;
*/
static bool forceSyncCommit = false;
+/* Flag for logging statements in a transaction. */
+bool xact_is_sampled = false;
+
/*
* Private context for transaction-abort work --- we reserve space for this
* at startup to ensure that AbortTransaction and AbortSubTransaction can work
@@ -1823,6 +1826,10 @@ StartTransaction(void)
s->state = TRANS_START;
s->transactionId = InvalidTransactionId; /* until assigned */
+ /* Determine if statements are logged in this transaction */
+ xact_is_sampled = log_xact_sample_rate != 0 && (log_xact_sample_rate == 1 ||
+ 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 f9ce3d8f22..44a59e1d4f 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -2194,6 +2194,8 @@ 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
@@ -2209,7 +2211,7 @@ 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;
@@ -2243,11 +2245,11 @@ 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 aa564d153a..e8a5784200 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -510,6 +510,7 @@ 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;
@@ -3366,6 +3367,18 @@ static struct config_real ConfigureNamesReal[] =
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 0.0 (never log) and 1.0 (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 cccb5f145a..d84287f703 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -493,6 +493,10 @@
# log_min_duration_statement. 1.0 logs all statements,
# 0 never logs.
+#log_transaction_sample_rate = 0.0 # Fraction of transactions whose statements
+ # are logged regardless of their duration. 1.0 logs all
+ # statements from all transactions, 0.0 never logs.
+
# - What to Log -
#debug_print_parse = off
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index e8579dcd47..dcdd80ff21 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 2712a774f7..34cebd540d 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;
