</para>

</sect1>

<sect1 id="logical-replication-restrictions">

<title>Restrictions</title>

<para>

Logical replication currently has the following restrictions or missing

functionality. These might be addressed in future releases.

</para>

<itemizedlist>

<listitem>

<para>

The database schema and DDL commands are not replicated. The initial

schema can be copied by hand using <literal>pg_dump

--schema-only</literal>. Subsequent schema changes would need to be kept

in sync manually. (Note, however, that there is no need for the schemas

to be absolutely the same on both sides.) Logical replication is robust

when schema definitions change in a live database: When the schema is

changed on the publisher and replicated data starts arriving at the

subscriber but does not fit into the table schema, replication will error

until the schema is updated. In many cases, intermittent errors can be

avoided by applying additive schema changes to the subscriber first.

</para>

</listitem>

<listitem>

<para>

Sequence data is not replicated. The data in serial or identity columns

backed by sequences will of course be replicated as part of the table,

but the sequence itself would still show the start value on the

subscriber. If the subscriber is used as a read-only database, then this

should typically not be a problem. If, however, some kind of switchover

or failover to the subscriber database is intended, then the sequences

would need to be updated to the latest values, either by copying the

current data from the publisher (perhaps

using <command>pg_dump</command>) or by determining a sufficiently high

value from the tables themselves.

</para>

</listitem>

<listitem>

<para>

<command>TRUNCATE</command> commands are not replicated. This can, of

course, be worked around by using <command>DELETE</command> instead. To

avoid accidental <command>TRUNCATE</command> invocations, you can revoke

the <literal>TRUNCATE</literal> privilege from tables.

</para>

</listitem>

<listitem>

<para>

Large objects (see <xref linkend="largeobjects">) are not replicated.

There is no workaround for that, other than storing data in normal

tables.

</para>

</listitem>

<listitem>

<para>

Replication is only possible from base tables to base tables. That is,

the tables on the publication and on the subscription side must be normal

tables, not views, materialized views, partition root tables, or foreign

tables. In the case of partitions, you can therefore replicate a

partition hierarchy one-to-one, but you cannot currently replicate to a

differently partitioned setup. Attempts to replicate tables other than

base tables will result in an error.

</para>

</listitem>

</itemizedlist>

</sect1>

<sect1 id="logical-replication-architecture">

<title>Architecture</title>