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Diffstat (limited to 'doc/src/sgml/ref/create_subscription.sgml')
| -rw-r--r-- | doc/src/sgml/ref/create_subscription.sgml | 87 |
1 files changed, 86 insertions, 1 deletions
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml index 57dec28a5df..b8cd15f3280 100644 --- a/doc/src/sgml/ref/create_subscription.sgml +++ b/doc/src/sgml/ref/create_subscription.sgml @@ -169,7 +169,9 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl <listitem> <para> Name of the publisher's replication slot to use. The default is - to use the name of the subscription for the slot name. + to use the name of the subscription for the slot name. The name cannot + be <literal>pg_conflict_detection</literal> as it is reserved for the + conflict detection. </para> <para> @@ -435,6 +437,89 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl </para> </listitem> </varlistentry> + + <varlistentry id="sql-createsubscription-params-with-retain-dead-tuples"> + <term><literal>retain_dead_tuples</literal> (<type>boolean</type>)</term> + <listitem> + <para> + Specifies whether the information (e.g., dead tuples, commit + timestamps, and origins) required for conflict detection on the + subscriber is retained. The default is <literal>false</literal>. + If set to <literal>true</literal>, a physical replication slot named + <quote><literal>pg_conflict_detection</literal></quote> will be + created on the subscriber to prevent the conflict information from + being removed. + </para> + + <para> + Note that the information useful for conflict detection is retained + only after the creation of the slot. You can verify the existence of + this slot by querying <link linkend="view-pg-replication-slots">pg_replication_slots</link>. + And even if multiple subscriptions on one node enable this option, + only one replication slot will be created. Also, + <varname>wal_level</varname> must be set to <literal>replica</literal> + or higher to allow the replication slot to be used. + </para> + + <caution> + <para> + Note that the information for conflict detection cannot be purged if + the subscription is disabled; thus, the information will accumulate + until the subscription is enabled. To prevent excessive accumulation, + it is recommended to disable <literal>retain_dead_tuples</literal> + if the subscription will be inactive for an extended period. + </para> + + <para> + Additionally when enabling <literal>retain_dead_tuples</literal> for + conflict detection in logical replication, it is important to design the + replication topology to balance data retention requirements with + overall system performance. This option provides minimal performance + overhead when applied appropriately. The following scenarios illustrate + effective usage patterns when enabling this option. + </para> + + <para> + a. Large Tables with Bidirectional Writes: + For large tables subject to concurrent writes on both publisher and + subscriber nodes, publishers can define row filters when creating + publications to segment data. This allows multiple subscriptions + to replicate exclusive subsets of the table in parallel, optimizing + the throughput. + </para> + + <para> + b. Write-Enabled Subscribers: + If a subscriber node is expected to perform write operations, replication + can be structured using multiple publications and subscriptions. By + distributing tables across these publications, the workload is spread among + several apply workers, improving concurrency and reducing contention. + </para> + + <para> + c. Read-Only Subscribers: + In configurations involving single or multiple publisher nodes + performing concurrent write operations, read-only subscriber nodes may + replicate changes without seeing a performance impact if it does index + scan. However, if the subscriber is impacted due to replication lag or + scan performance (say due to sequential scans), it needs to follow one + of the two previous strategies to distribute the workload on the + subscriber. + </para> + </caution> + + <para> + This option cannot be enabled if the publisher is a physical standby. + </para> + + <para> + Enabling this option ensures retention of information useful for + conflict detection solely for changes occurring locally on the + publisher. For the changes originating from different origins, + reliable conflict detection cannot be guaranteed. + </para> + </listitem> + </varlistentry> </variablelist></para> </listitem> |