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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>31.4. Restrictions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="logical-replication-conflicts.html" title="31.3. Conflicts" /><link rel="next" href="logical-replication-architecture.html" title="31.5. Architecture" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">31.4. Restrictions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="logical-replication-conflicts.html" title="31.3. Conflicts">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="logical-replication.html" title="Chapter 31. Logical Replication">Up</a></td><th width="60%" align="center">Chapter 31. Logical Replication</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="logical-replication-architecture.html" title="31.5. Architecture">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LOGICAL-REPLICATION-RESTRICTIONS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">31.4. Restrictions</h2></div></div></div><p>
Logical replication currently has the following restrictions or missing
functionality. These might be addressed in future releases.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
The database schema and DDL commands are not replicated. The initial
schema can be copied by hand using <code class="literal">pg_dump
--schema-only</code>. 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.
</p></li><li class="listitem"><p>
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 <code class="command">pg_dump</code>) or by determining a sufficiently high
value from the tables themselves.
</p></li><li class="listitem"><p>
Replication of <code class="command">TRUNCATE</code> commands is supported, but
some care must be taken when truncating groups of tables connected by
foreign keys. When replicating a truncate action, the subscriber will
truncate the same group of tables that was truncated on the publisher,
either explicitly specified or implicitly collected via
<code class="literal">CASCADE</code>, minus tables that are not part of the
subscription. This will work correctly if all affected tables are part
of the same subscription. But if some tables to be truncated on the
subscriber have foreign-key links to tables that are not part of the same
(or any) subscription, then the application of the truncate action on the
subscriber will fail.
</p></li><li class="listitem"><p>
Large objects (see <a class="xref" href="largeobjects.html" title="Chapter 35. Large Objects">Chapter 35</a>) are not replicated.
There is no workaround for that, other than storing data in normal
tables.
</p></li><li class="listitem"><p>
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.
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