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Marginal comments and docs cleanup. 

Fix up some imprecise comments and poor markup from ba79cb5dc.  Also try
to convert the documentation of log_min_duration_sample and friends into
passable English.
This commit is contained in:
Tom Lane 2020-03-10 17:34:01 -04:00
parent d1e241c226
commit c8e8b2f9df
3 changed files with 49 additions and 61 deletions
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97
doc/src/sgml/config.sgml
View File

@ -5984,13 +5984,13 @@ local0.* /var/log/postgresql
<para>
Causes the duration of each completed statement to be logged
if the statement ran for at least the specified amount of time.
If this value is specified without units, it is taken as milliseconds.
Setting this to zero prints all statement durations.
Minus-one (the default) disables logging statement durations.
For example, if you set it to <literal>250ms</literal>
then all SQL statements that run 250ms or longer will be
logged. Enabling this parameter can be helpful in tracking down
unoptimized queries in your applications.
If this value is specified without units, it is taken as milliseconds.
Setting this to zero prints all statement durations.
Minus-one (the default) disables logging statement durations.
Only superusers can change this setting.
</para>
@ -6030,49 +6030,39 @@ local0.* /var/log/postgresql
</term>
<listitem>
<para>
Allows to sample the logging of the duration of each completed
statement if the statement ran for at least the specified amount of
time. If this value is specified without units, it is taken as milliseconds.
Allows sampling the duration of completed statements that ran for
at least the specified amount of time. This produces the same
kind of log entries as
<xref linkend="guc-log-min-duration-statement"/>, but only for a
subset of the executed statements, with sample rate controlled by
<xref linkend="guc-log-statement-sample-rate"/>.
For example, if you set it to <literal>100ms</literal> then all
SQL statements that run 100ms or longer will be considered for
sampling. Enabling this parameter can be helpful when the
traffic is too high to log all queries.
If this value is specified without units, it is taken as milliseconds.
Setting this to zero samples all statement durations.
Minus-one (the default) disables sampling statement durations.
For example, if you set it to <literal>250ms</literal>
then all SQL statements that run 250ms or longer will be considered
for sampling, with sample rate is controlled by <xref linkend="guc-log-statement-sample-rate"/>.
Enabling this parameter can be helpful when the traffic too high to
sample all queries.
Only superusers can change this setting.
</para>
<para>
This option has lower priority than <xref linkend="guc-log-min-duration-statement"/>,
meaning that statements with durations exceeding <xref linkend="guc-log-min-duration-statement"/>
are not subject to sampling and are always logged.
This setting has lower priority
than <varname>log_min_duration_statement</varname>, meaning that
statements with durations
exceeding <varname>log_min_duration_statement</varname> are not
subject to sampling and are always logged.
</para>
<para>
For clients using extended query protocol, durations of the Parse,
Bind, and Execute steps are logged independently.
Other notes for <varname>log_min_duration_statement</varname>
apply also to this setting.
</para>
<note>
<para>
When using this option together with
<xref linkend="guc-log-statement"/>,
the text of statements that are logged because of
<varname>log_statement</varname> will not be repeated in the
duration log message.
If you are not using <application>syslog</application>, it is recommended
that you log the PID or session ID using
<xref linkend="guc-log-line-prefix"/>
so that you can link the statement message to the later
duration message using the process ID or session ID.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry id="guc-log-statement-sample-rate" xreflabel="log_statement_sample_rate">
<term><varname>log_statement_sample_rate</varname> (<type>real</type>)
<term><varname>log_statement_sample_rate</varname> (<type>floating point</type>)
<indexterm>
<primary><varname>log_statement_sample_rate</varname> configuration parameter</primary>
</indexterm>
@ -6080,43 +6070,40 @@ local0.* /var/log/postgresql
<listitem>
<para>
Determines the fraction of statements with duration exceeding
<xref linkend="guc-log-min-duration-sample"/> to be logged.
This is a statistical parameter, for example <literal>0.5</literal>
means there is statistically one in two chances to log the statement.
The default is <literal>1.0</literal>, meaning log all such
<xref linkend="guc-log-min-duration-sample"/> that will be logged.
Sampling is stochastic, for example <literal>0.5</literal> means
there is statistically one chance in two that any given statement
will be logged.
The default is <literal>1.0</literal>, meaning to log all sampled
statements.
Setting this to zero disables sampling logging, same as setting
Setting this to zero disables sampled statement-duration logging,
the same as setting
<varname>log_min_duration_sample</varname> to
<literal>-1</literal>.
<varname>log_statement_sample_rate</varname> is helpful when the
traffic is too high to log all queries.
Only superusers can change this setting.
</para>
<note>
<para>
Like all statement-logging options, this option can add significant
overhead.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry id="guc-log-transaction-sample-rate" xreflabel="log_transaction_sample_rate">
<term><varname>log_transaction_sample_rate</varname> (<type>real</type>)
<term><varname>log_transaction_sample_rate</varname> (<type>floating point</type>)
<indexterm>
<primary><varname>log_transaction_sample_rate</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Set the fraction of transactions whose statements are all logged,
Sets the fraction of transactions whose statements are all logged,
in addition to statements logged for other reasons. It applies to
each new transaction regardless of its statements' durations.
The default is <literal>0</literal>, meaning not to log statements
from any additional 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.
Sampling is stochastic, for example <literal>0.1</literal> means
there is statistically one chance in ten that any given transaction
will be logged.
<varname>log_transaction_sample_rate</varname> can be helpful to
construct a sample of transactions.
The default is <literal>0</literal>, meaning not to log
statements from any additional transactions. Setting this
to <literal>1</literal> logs all statements of all transactions.
Only superusers can change this setting.
</para>
<note>
@ -6632,9 +6619,9 @@ log_line_prefix = '%m [%p] %q%u@%d/%a '
<para>
Controls whether bind parameters are logged when a statement is logged
as a result of <xref linkend="guc-log-min-error-statement"/>.
It adds some overhead, as postgres will compute and store textual
representations of parameter values in memory for all statements,
even if they eventually do not get logged.
It adds some overhead, as <productname>PostgreSQL</productname> will
compute and store textual representations of parameter values in
memory for all statements, even if they eventually do not get logged.
This setting has no effect on statements logged due to
<xref linkend="guc-log-min-duration-statement"/> or
<xref linkend="guc-log-statement"/> settings, as they are always logged

11
src/backend/nodes/params.c
View File

@ -262,16 +262,16 @@ RestoreParamList(char **start_address)
/*
* BuildParamLogString
* Return a string that represent the parameter list, for logging.
* Return a string that represents the parameter list, for logging.
*
* If caller already knows textual representations for some parameters, it can
* pass an array of exactly params->numParams values as knownTextValues, which
* can contain NULLs for any unknown individual values. NULL can be given if
* no parameters are known.
*
* If maxlen is not zero, that's the maximum number of characters of the
* input string printed; an ellipsis is added if more characters exist.
* (Added quotes are not considered.)
* If maxlen is not zero, that's the maximum number of bytes of any one
* parameter value to be printed; an ellipsis is added if the string is
* longer. (Added quotes are not considered in this calculation.)
*/
char *
BuildParamLogString(ParamListInfo params, char **knownTextValues, int maxlen)
@ -282,7 +282,8 @@ BuildParamLogString(ParamListInfo params, char **knownTextValues, int maxlen)
/*
* NB: think not of returning params->paramValuesStr! It may have been
* generated with a different maxlen, and so unsuitable.
* generated with a different maxlen, and so be unsuitable. Besides that,
* this is the function used to create that string.
*/
/*

2
src/backend/utils/mb/stringinfo_mb.c
View File

@ -26,7 +26,7 @@
/*
* appendStringInfoStringQuoted
*
* Append up to maxlen characters from s to str, or the whole input string if
* Append up to maxlen bytes from s to str, or the whole input string if
* maxlen <= 0, adding single quotes around it and doubling all single quotes.
* Add an ellipsis if the copy is incomplete.
*/