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Avoid a few more SET DATA TYPE table rewrites.

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When the new type is an unconstrained domain over the old type, we don't
need to rewrite the table.

Noah Misch and Robert Haas
This commit is contained in:
Robert Haas
2011-02-14 23:17:35 -05:00
parent 8e1124eeeb
commit 0d90dc16f8
2 changed files with 24 additions and 11 deletions
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15
doc/src/sgml/ref/alter_table.sgml
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@ -766,13 +766,14 @@ ALTER TABLE <replaceable class="PARAMETER">name</replaceable>
<para>
Adding a column with a non-null default or changing the type of an
existing column will require the entire table and indexes to be rewritten.
As an exception, if the old type type is binary coercible to the new
type and the <literal>USING</> clause does not change the column contents,
a table rewrite is not needed, but any indexes on the affected columns
must still be rebuilt. Adding or removing a system <literal>oid</> column
also requires rewriting the entire table. Table and/or index rebuilds may
take a significant amount of time for a large table; and will temporarily
require as much as double the disk space.
As an exception, if the <literal>USING</> clause does not change the column
contents and the old type is either binary coercible to the new type or
an unconstrained domain over the new type, a table rewrite is not needed,
but any indexes on the affected columns must still be rebuilt. Adding or
removing a system <literal>oid</> column also requires rewriting the entire
table. Table and/or index rebuilds may take a significant amount of time
for a large table; and will temporarily require as much as double the disk
space.
</para>
<para>