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| -rw-r--r-- | doc/src/sgml/logicaldecoding.sgml | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml index c42082002e0..484915d0422 100644 --- a/doc/src/sgml/logicaldecoding.sgml +++ b/doc/src/sgml/logicaldecoding.sgml @@ -12,7 +12,6 @@ <para> Changes are sent out in streams identified by logical replication slots. - Each stream outputs each change exactly once. </para> <para> @@ -204,8 +203,7 @@ $ pg_recvlogical -d postgres --slot test --drop-slot In the context of logical replication, a slot represents a stream of changes that can be replayed to a client in the order they were made on the origin server. Each slot streams a sequence of changes from a single - database, sending each change exactly once (except when peeking forward - in the stream). + database. </para> <note> @@ -222,6 +220,20 @@ $ pg_recvlogical -d postgres --slot test --drop-slot </para> <para> + A logical slot will emit each change just once in normal operation. + The current position of each slot is persisted only at checkpoint, so in + the case of a crash the slot may return to an earlier LSN, which will + then cause recent changes to be resent when the server restarts. + Logical decoding clients are responsible for avoiding ill effects from + handling the same message more than once. Clients may wish to record + the last LSN they saw when decoding and skip over any repeated data or + (when using the replication protocol) request that decoding start from + that LSN rather than letting the server determine the start point. + The Replication Progress Tracking feature is designed for this purpose, + refer to <link linkend="replication-origins">replication origins</link>. + </para> + + <para> Multiple independent slots may exist for a single database. Each slot has its own state, allowing different consumers to receive changes from different points in the database change stream. For most applications, a |