Doc: mention CREATE+ATTACH PARTITION with CREATE TABLE...PARTITION OF.

Clarify that ATTACH/DETACH PARTITION can be used to perform partition
maintenance with less locking than straight CREATE TABLE/DROP TABLE.
This was already stated in some places, but not emphasized.

Back-patch to v14 where DETACH PARTITION CONCURRENTLY was added.
(We had lower lock levels for ATTACH PARTITION before that, but
this wording wouldn't apply.)

Justin Pryzby, reviewed by Robert Treat and Jakub Wartak;
a little further wordsmithing by me

Discussion: https://postgr.es/m/20220718143304.GC18011@telsasoft.com

diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 5179125510b1e8b2c7267376765727d0dbbf995f..91c036d1cbead540c4f5690b1b38b5e4ad680e52 100644 (file)
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4114,9 +4114,15 @@ CREATE TABLE measurement_y2008m02 PARTITION OF measurement
 </programlisting>
 
      As an alternative, it is sometimes more convenient to create the
-     new table outside the partition structure, and make it a proper
+     new table outside the partition structure, and attach it as a
      partition later. This allows new data to be loaded, checked, and
      transformed prior to it appearing in the partitioned table.
+     Moreover, the <literal>ATTACH PARTITION</literal> operation requires
+     only <literal>SHARE UPDATE EXCLUSIVE</literal> lock on the
+     partitioned table, as opposed to the <literal>ACCESS
+     EXCLUSIVE</literal> lock that is required by <command>CREATE TABLE
+     ... PARTITION OF</command>, so it is more friendly to concurrent
+     operations on the partitioned table.
      The <literal>CREATE TABLE ... LIKE</literal> option is helpful
      to avoid tediously repeating the parent table's definition:
 
@@ -4136,11 +4142,6 @@ ALTER TABLE measurement ATTACH PARTITION measurement_y2008m02
 </programlisting>
     </para>
 
-    <para>
-     The <command>ATTACH PARTITION</command> command requires taking a
-     <literal>SHARE UPDATE EXCLUSIVE</literal> lock on the partitioned table.
-    </para>
-
     <para>
      Before running the <command>ATTACH PARTITION</command> command, it is
      recommended to create a <literal>CHECK</literal> constraint on the table to

diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index a03dee4afef538fd3c5cb3f68550c5ca25ceb290..10ef699fab92016188d20fa335c874f017ea2403 100644 (file)
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -615,12 +615,24 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
      </para>
 
      <para>
-      Operations such as TRUNCATE which normally affect a table and all of its
+      Operations such as <command>TRUNCATE</command>
+      which normally affect a table and all of its
       inheritance children will cascade to all partitions, but may also be
-      performed on an individual partition.  Note that dropping a partition
-      with <literal>DROP TABLE</literal> requires taking an <literal>ACCESS
-      EXCLUSIVE</literal> lock on the parent table.
+      performed on an individual partition.
      </para>
+
+     <para>
+      Note that creating a partition using <literal>PARTITION OF</literal>
+      requires taking an <literal>ACCESS EXCLUSIVE</literal> lock on the
+      parent partitioned table.  Likewise, dropping a partition
+      with <command>DROP TABLE</command> requires taking
+      an <literal>ACCESS EXCLUSIVE</literal> lock on the parent table.
+      It is possible to use <link linkend="sql-altertable"><command>ALTER
+      TABLE ATTACH/DETACH PARTITION</command></link> to perform these
+      operations with a weaker lock, thus reducing interference with
+      concurrent operations on the partitioned table.
+     </para>
+
     </listitem>
    </varlistentry>