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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>30.4. 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 V1.79.1" /><link rel="prev" href="logical-replication-conflicts.html" title="30.3. Conflicts" /><link rel="next" href="logical-replication-architecture.html" title="30.5. 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">30.4. Restrictions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="logical-replication-conflicts.html" title="30.3. Conflicts">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="logical-replication.html" title="Chapter 30. Logical Replication">Up</a></td><th width="60%" align="center">Chapter 30. Logical Replication</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="logical-replication-architecture.html" title="30.5. 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">30.4. 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 34. Large Objects">Chapter 34</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.
- </p></li></ul></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="logical-replication-conflicts.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="logical-replication.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="logical-replication-architecture.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">30.3. Conflicts </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 30.5. Architecture</td></tr></table></div></body></html>
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