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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
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@ -3331,6 +3331,44 @@ ALTER TABLE measurement ATTACH PARTITION measurement_y2008m02
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One may then drop the constraint after <command>ATTACH PARTITION</command>
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is finished, because it is no longer necessary.
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</para>
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<para>
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As explained above, it is possible to create indexes on partitioned tables
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and they are applied automatically to the entire hierarchy. This is very
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convenient, as not only the existing partitions will become indexed, but
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also any partitions that are created in the future will. One limitation is
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that it's not possible to use the <literal>CONCURRENTLY</literal>
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qualifier when creating such a partitioned index. To overcome long lock
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times, it is possible to use <command>CREATE INDEX ON ONLY</command>
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the partitioned table; such an index is marked invalid, and the partitions
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do not get the index applied automatically. The indexes on partitions can
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be created separately using <literal>CONCURRENTLY</literal>, and later
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<firstterm>attached</firstterm> to the index on the parent using
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<command>ALTER INDEX .. ATTACH PARTITION</command>. Once indexes for all
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partitions are attached to the parent index, the parent index is marked
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valid automatically. Example:
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<programlisting>
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CREATE INDEX measurement_usls_idx ON ONLY measurement (unitsales);
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CREATE INDEX measurement_usls_200602_idx
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ON measurement_y2006m02 (unitsales);
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ALTER INDEX measurement_usls_idx
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ATTACH PARTITION measurement_usls_200602_idx;
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...
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</programlisting>
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This technique can be used with <literal>UNIQUE</literal> and
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<literal>PRIMARY KEY</literal> constraints too; the indexes are created
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implicitly when the constraint is created. Example:
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<programlisting>
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ALTER TABLE ONLY measurement ADD UNIQUE (city_id, logdate);
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ALTER TABLE measurement_y2006m02 ADD UNIQUE (city_id, logdate);
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ALTER INDEX measurement_city_id_logdate_key
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ATTACH PARTITION measurement_y2006m02_city_id_logdate_key;
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...
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</programlisting>
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</para>
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</sect3>
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<sect3 id="ddl-partitioning-declarative-limitations">
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