diff options
| -rw-r--r-- | doc/src/sgml/ddl.sgml | 12 | ||||
| -rw-r--r-- | doc/src/sgml/ref/alter_table.sgml | 27 |
2 files changed, 20 insertions, 19 deletions
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml index 12905c97211..9235797af2d 100644 --- a/doc/src/sgml/ddl.sgml +++ b/doc/src/sgml/ddl.sgml @@ -3308,13 +3308,13 @@ ALTER TABLE measurement ATTACH PARTITION measurement_y2008m02 <para> Before running the <command>ATTACH PARTITION</> command, it is recommended to create a <literal>CHECK</> constraint on the table to - be attached describing the desired partition constraint. That way, + be attached matching the desired partition constraint. That way, the system will be able to skip the scan to validate the implicit - partition constraint. Without such a constraint, the table will be - scanned to validate the partition constraint while holding an - <literal>ACCESS EXCLUSIVE</literal> lock on the parent table. - One may then drop the constraint after <command>ATTACH PARTITION</> - is finished, because it is no longer necessary. + partition constraint. Without the <literal>CHECK</> constraint, + the table will be scanned to validate the partition constraint while + holding an <literal>ACCESS EXCLUSIVE</literal> lock on the parent table. + It may be desired to drop the redundant <literal>CHECK</> constraint + after <command>ATTACH PARTITION</> is finished. </para> </sect3> diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml index dae63077eed..30644170ca5 100644 --- a/doc/src/sgml/ref/alter_table.sgml +++ b/doc/src/sgml/ref/alter_table.sgml @@ -781,23 +781,24 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> <literal>FOREIGN KEY</literal> constraints are not considered. If any of the <literal>CHECK</literal> constraints of the table being attached is marked <literal>NO INHERIT</literal>, the command will fail; - such a constraint must be recreated without the <literal>NO INHERIT</literal> - clause. + such constraints must be recreated without the + <literal>NO INHERIT</literal> clause. </para> <para> If the new partition is a regular table, a full table scan is performed - to check that no existing row in the table violates the partition - constraint. It is possible to avoid this scan by adding a valid - <literal>CHECK</literal> constraint to the table that would allow only - the rows satisfying the desired partition constraint before running this - command. It will be determined using such a constraint that the table - need not be scanned to validate the partition constraint. This does not - work, however, if any of the partition keys is an expression and the - partition does not accept <literal>NULL</literal> values. If attaching - a list partition that will not accept <literal>NULL</literal> values, - also add <literal>NOT NULL</literal> constraint to the partition key - column, unless it's an expression. + to check that existing rows in the table do not violate the partition + constraint. It is possible to avoid this scan by adding a valid + <literal>CHECK</literal> constraint to the table that allows only + rows satisfying the desired partition constraint before running this + command. The <literal>CHECK</literal> constraint will be used to + determine that the table need not be scanned to validate the partition + constraint. This does not work, however, if any of the partition keys + is an expression and the partition does not accept + <literal>NULL</literal> values. If attaching a list partition that will + not accept <literal>NULL</literal> values, also add + <literal>NOT NULL</literal> constraint to the partition key column, + unless it's an expression. </para> <para> |