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Reconsider pg_stat_subscription_workers view.

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It was decided (refer to the Discussion link below) that the stats
collector is not an appropriate place to store the error information of
subscription workers.

This patch changes the pg_stat_subscription_workers view (introduced by
commit 8d74fc96db) so that it stores only statistics counters:
apply_error_count and sync_error_count, and has one entry for
each subscription. The removed error information such as error-XID and
the error message would be stored in another way in the future which is
more reliable and persistent.

After removing these error details, there is no longer any relation
information, so the subscription statistics are now a cluster-wide
statistics.

The patch also changes the view name to pg_stat_subscription_stats since
the word "worker" is an implementation detail that we use one worker for
one tablesync and one apply.

Author: Masahiko Sawada, based on suggestions by Andres Freund
Reviewed-by: Peter Smith, Haiying Tang, Takamichi Osumi, Amit Kapila
Discussion: https://postgr.es/m/20220125063131.4cmvsxbz2tdg6g65@alap3.anarazel.de
This commit is contained in:
Amit Kapila
2022-03-01 06:17:52 +05:30
parent 54bd1e43ca
commit 7a85073290
14 changed files with 583 additions and 865 deletions
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4
doc/src/sgml/logical-replication.sgml
View File

@ -346,9 +346,7 @@
<para>
A conflict will produce an error and will stop the replication; it must be
resolved manually by the user. Details about the conflict can be found in
<link linkend="monitoring-pg-stat-subscription-workers">
<structname>pg_stat_subscription_workers</structname></link> and the
subscriber's server log.
the subscriber's server log.
</para>
<para>

99
doc/src/sgml/monitoring.sgml
View File

@ -628,11 +628,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
</row>
<row>
<entry><structname>pg_stat_subscription_workers</structname><indexterm><primary>pg_stat_subscription_workers</primary></indexterm></entry>
<entry>One row per subscription worker, showing statistics about errors
that occurred on that subscription worker.
See <link linkend="monitoring-pg-stat-subscription-workers">
<structname>pg_stat_subscription_workers</structname></link> for details.
<entry><structname>pg_stat_subscription_stats</structname><indexterm><primary>pg_stat_subscription_stats</primary></indexterm></entry>
<entry>One row per subscription, showing statistics about errors.
See <link linkend="monitoring-pg-stat-subscription-stats">
<structname>pg_stat_subscription_stats</structname></link> for details.
</entry>
</row>
@ -3063,23 +3062,20 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
</sect2>
<sect2 id="monitoring-pg-stat-subscription-workers">
<title><structname>pg_stat_subscription_workers</structname></title>
<sect2 id="monitoring-pg-stat-subscription-stats">
<title><structname>pg_stat_subscription_stats</structname></title>
<indexterm>
<primary>pg_stat_subscription_workers</primary>
<primary>pg_stat_subscription_stats</primary>
</indexterm>
<para>
The <structname>pg_stat_subscription_workers</structname> view will contain
one row per subscription worker on which errors have occurred, for workers
applying logical replication changes and workers handling the initial data
copy of the subscribed tables. The statistics entry is removed when the
corresponding subscription is dropped.
The <structname>pg_stat_subscription_stats</structname> view will contain
one row per subscription.
</para>
<table id="pg-stat-subscription-workers" xreflabel="pg_stat_subscription_workers">
<title><structname>pg_stat_subscription_workers</structname> View</title>
<table id="pg-stat-subscription-stats" xreflabel="pg_stat_subscription_stats">
<title><structname>pg_stat_subscription_stats</structname> View</title>
<tgroup cols="1">
<thead>
<row>
@ -3113,72 +3109,31 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>subrelid</structfield> <type>oid</type>
<structfield>apply_error_count</structfield> <type>bigint</type>
</para>
<para>
OID of the relation that the worker is synchronizing; null for the
main apply worker
Number of times an error occurred while applying changes
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>last_error_relid</structfield> <type>oid</type>
<structfield>sync_error_count</structfield> <type>bigint</type>
</para>
<para>
OID of the relation that the worker was processing when the
error occurred
Number of times an error occurred during the initial table
synchronization
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>last_error_command</structfield> <type>text</type>
<structfield>stats_reset</structfield> <type>timestamp with time zone</type>
</para>
<para>
Name of command being applied when the error occurred. This field
is null if the error was reported during the initial data copy.
Time at which these statistics were last reset
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>last_error_xid</structfield> <type>xid</type>
</para>
<para>
Transaction ID of the publisher node being applied when the error
occurred. This field is null if the error was reported
during the initial data copy.
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>last_error_count</structfield> <type>uint8</type>
</para>
<para>
Number of consecutive times the error occurred
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>last_error_message</structfield> <type>text</type>
</para>
<para>
The error message
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>last_error_time</structfield> <type>timestamp with time zone</type>
</para>
<para>
Last time at which this error occurred
</para></entry>
</row>
</tbody>
</tgroup>
</table>
@ -5320,22 +5275,16 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_stat_reset_subscription_worker</primary>
<primary>pg_stat_reset_subscription_stats</primary>
</indexterm>
<function>pg_stat_reset_subscription_worker</function> ( <parameter>subid</parameter> <type>oid</type> <optional>, <parameter>relid</parameter> <type>oid</type> </optional> )
<function>pg_stat_reset_subscription_stats</function> ( <type>oid</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Resets the statistics of subscription workers running on the
subscription with <parameter>subid</parameter> shown in the
<structname>pg_stat_subscription_workers</structname> view. If the
argument <parameter>relid</parameter> is not <literal>NULL</literal>,
resets statistics of the subscription worker handling the initial data
copy of the relation with <parameter>relid</parameter>. Otherwise,
resets the subscription worker statistics of the main apply worker.
If the argument <parameter>relid</parameter> is omitted, resets the
statistics of all subscription workers running on the subscription
with <parameter>subid</parameter>.
Resets statistics for a single subscription shown in the
<structname>pg_stat_subscription_stats</structname> view to zero. If
the argument is <literal>NULL</literal>, reset statistics for all
subscriptions.
</para>
<para>
This function is restricted to superusers by default, but other users