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Document piecemeal construction of partitioned indexes 

Continuous operation cannot be achieved without applying this technique,
so it needs to be properly described.

Author: Álvaro Herrera
Reported-by: Tom Lane
Discussion: https://postgr.es/m/8756.1556302759@sss.pgh.pa.us
This commit is contained in:
Alvaro Herrera 2019-06-04 16:42:40 -04:00
parent ece9dc40d6
commit 5efd604ec0
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doc/src/sgml/ddl.sgml
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@ -3948,6 +3948,44 @@ ALTER TABLE measurement ATTACH PARTITION measurement_y2008m02
One may then drop the constraint after <command>ATTACH PARTITION</command>
is finished, because it is no longer necessary.
</para>
<para>
As explained above, it is possible to create indexes on partitioned tables
and they are applied automatically to the entire hierarchy. This is very
convenient, as not only the existing partitions will become indexed, but
also any partitions that are created in the future will. One limitation is
that it's not possible to use the <literal>CONCURRENTLY</literal>
qualifier when creating such a partitioned index. To overcome long lock
times, it is possible to use <command>CREATE INDEX ON ONLY</command>
the partitioned table; such an index is marked invalid, and the partitions
do not get the index applied automatically. The indexes on partitions can
be created separately using <literal>CONCURRENTLY</literal>, and later
<firstterm>attached</firstterm> to the index on the parent using
<command>ALTER INDEX .. ATTACH PARTITION</command>. Once indexes for all
partitions are attached to the parent index, the parent index is marked
valid automatically. Example:
<programlisting>
CREATE INDEX measurement_usls_idx ON ONLY measurement (unitsales);
CREATE INDEX measurement_usls_200602_idx
ON measurement_y2006m02 (unitsales);
ALTER INDEX measurement_usls_idx
ATTACH PARTITION measurement_usls_200602_idx;
...
</programlisting>
This technique can be used with <literal>UNIQUE</literal> and
<literal>PRIMARY KEY</literal> constraints too; the indexes are created
implicitly when the constraint is created. Example:
<programlisting>
ALTER TABLE ONLY measurement ADD UNIQUE (city_id, logdate);
ALTER TABLE measurement_y2006m02 ADD UNIQUE (city_id, logdate);
ALTER INDEX measurement_city_id_logdate_key
ATTACH PARTITION measurement_y2006m02_city_id_logdate_key;
...
</programlisting>
</para>
</sect3>
<sect3 id="ddl-partitioning-declarative-limitations">