diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/ref/alter_table.sgml | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml index 6166b263345..9cef1f101eb 100644 --- a/doc/src/sgml/ref/alter_table.sgml +++ b/doc/src/sgml/ref/alter_table.sgml @@ -391,7 +391,21 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM </term> <listitem> <para> - This sets the compression method for a column. The supported compression + This sets the compression method to be used for data inserted into a column. + + This does not cause the table to be rewritten, so existing data may still + be compressed with other compression methods. If the table is rewritten with + <command>VACUUM FULL</command> or <command>CLUSTER</command>, or restored + with <application>pg_restore</application>, then all tuples are rewritten + with the configured compression methods. + + Also, note that when data is inserted from another relation (for example, + by <command>INSERT ... SELECT</command>), tuples from the source data are + not necessarily detoasted, and any previously compressed data is retained + with its existing compression method, rather than recompressing with the + compression methods of the target columns. + + The supported compression methods are <literal>pglz</literal> and <literal>lz4</literal>. <literal>lz4</literal> is available only if <literal>--with-lz4</literal> was used when building <productname>PostgreSQL</productname>. |