<para>

Changes are sent out in streams identified by logical replication slots.

Each stream outputs each change exactly once.

</para>

<para>

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>

independently of the connection using them and are crash-safe.

</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