recovery_min_apply_delay

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<p>
        By default, a standby server restores WAL records from the
        sending server as soon as possible. It may be useful to have a time-delayed
        copy of the data, offering opportunities to correct data loss errors.
        This parameter allows you to delay recovery by a specified amount
        of time.  For example, if
        you set this parameter to <code class="literal">5min</code>, the standby will
        replay each transaction commit only when the system time on the standby
        is at least five minutes past the commit time reported by the primary.
        If this value is specified without units, it is taken as milliseconds.
        The default is zero, adding no delay.
       </p><p>
        It is possible that the replication delay between servers exceeds the
        value of this parameter, in which case no delay is added.
        Note that the delay is calculated between the WAL time stamp as written
        on primary and the current time on the standby. Delays in transfer
        because of network lag or cascading replication configurations
        may reduce the actual wait time significantly. If the system
        clocks on primary and standby are not synchronized, this may lead to
        recovery applying records earlier than expected; but that is not a
        major issue because useful settings of this parameter are much larger
        than typical time deviations between servers.
       </p><p>
        The delay occurs only on WAL records for transaction commits.
        Other records are replayed as quickly as possible, which
        is not a problem because MVCC visibility rules ensure their effects
        are not visible until the corresponding commit record is applied.
       </p><p>
        The delay occurs once the database in recovery has reached a consistent
        state, until the standby is promoted or triggered. After that the standby
        will end recovery without further waiting.
       </p><p>
        WAL records must be kept on the standby until they are ready to be
        applied. Therefore, longer delays will result in a greater accumulation
        of WAL files, increasing disk space requirements for the standby's
        <code class="filename">pg_wal</code> directory.
       </p><p>
        This parameter is intended for use with streaming replication deployments;
        however, if the parameter is specified it will be honored in all cases
        except crash recovery.

        <code class="varname">hot_standby_feedback</code> will be delayed by use of this feature
        which could lead to bloat on the primary; use both together with care.

        </p><div class="warning"><h3 class="title">Warning</h3><p>
          Synchronous replication is affected by this setting when <code class="varname">synchronous_commit</code>
          is set to <code class="literal">remote_apply</code>; every <code class="literal">COMMIT</code>
          will need to wait to be applied.
         </p></div><p>
</p><p>
        This parameter can only be set in the <code class="filename">postgresql.conf</code>
        file or on the server command line.
       </p>

documentation revision

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