Re: Small issues with CREATE TABLE COMPRESSION

On Thu, Apr 29, 2021 at 9:31 AM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
>
> On Tue, Apr 27, 2021 at 03:22:25PM +0900, Michael Paquier wrote:
> > Hi all,
>
> > And so, ALTER MATERIALIZED VIEW supports SET COMPRESSION but this is
> > not mentioned in its docs:
> > https://www.postgresql.org/docs/devel/sql-altermaterializedview.html
> >
> > psql could have tab completion support for that.
>
> Actually ALTER matview ALTER col has no tab completion at all, right ?

Right.

> Good point. I started with this.
>
> diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
> index 39927be41e..8cceea41d0 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>.

Your documentation looks fine to me.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com