</indexterm>

<listitem>

<para>

<varname>commit_delay</varname> adds a time delay,set in

<varname>commit_delay</varname> adds a time delay,measured in

microseconds, before a WAL flush is initiated. This can improve

group commit throughput by allowing a larger number of transactions

to commit via a single WAL flush, if system load is high enough

flush. Because the delay is just wasted if no other transactions

become ready to commit, a delay is only performed if at least

<varname>commit_siblings</varname> other transactions are active

immediately before a flush would otherwise have been initiated.

when a flush is about to be initiated. Also, no delays are

performed if <varname>fsync</varname> is disabled.

The default <varname>commit_delay</> is zero (no delay).

Only superusers can change this setting.

</para>

<para>

In <productname>PostgreSQL</> releases prior to 9.3,

<varname>commit_delay</varname> behaved differently and was much

less effective: it affected only commits, rather than all WAL flushes,

and waited for the entire configured delay even if the WAL flush

was completed sooner. Beginning in <productname>PostgreSQL</> 9.3,

the first process that becomes ready to flush waits for the configured

interval, while subsequent processes wait only until the leader

completes the flush. The default <varname>commit_delay</> is zero

(no delay). No delays are performed unless <varname>fsync</varname>

is enabled.

completes the flush operation.

</para>

</listitem>

</varlistentry>