docs: adjustments for streaming standbys that disconnect frequently

Document problems when disconnection causes loss of hot_standby_feedback
and suggest adjusting max_standby_archive_delay and
max_standby_streaming_delay.

Initial patch by Marko Tiikkaja, adjustments by me

diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index ecb51c4b1a224a141bec49f045e7e0bded11f204..39d7467ddd10a9b0dd7eadd0fda6186ee3b6b239 100644 (file)
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -1889,9 +1889,14 @@ if (!triggered)
     situation will be no worse than if the standby queries were running
     directly on the primary server, and you are still getting the benefit of
     off-loading execution onto the standby.
     situation will be no worse than if the standby queries were running
     directly on the primary server, and you are still getting the benefit of
     off-loading execution onto the standby.

-    <varname>max_standby_archive_delay</> must be kept large in this case,
-    because delayed WAL files might already contain entries that conflict with
-    the desired standby queries.
+    If standby servers connect and disconnect frequently, you
+    might want to make adjustments to handle the period when
+    <varname>hot_standby_feedback</> feedback is not being provided.
+    For example, consider increasing <varname>max_standby_archive_delay</>
+    so that queries are not rapidly cancelled by conflicts in WAL archive
+    files during disconnected periods.  You should also consider increasing
+    <varname>max_standby_streaming_delay</> to avoid rapid cancellations
+    by newly-arrived streaming WAL entries after reconnection.

    </para>
 
    <para>
    </para>
 
    <para>