On Thu, Nov 29, 2007 at 11:42:18AM -0500, Bruce Momjian wrote:
> Joshua D. Drake wrote:
> > Tom Lane wrote:
> > > "Joshua D. Drake" <[EMAIL PROTECTED]> writes:
> > >> Rules are extremely slow in comparisons and not anywhere near as
> > >> flexible. As I said up post yesterday... they work well in the basic
> > >> partitioning configuration but anything else they are extremely
> > >> deficient.
> > >
> > > I think that the above claim is exceedingly narrow-minded.
> >
> > We are talking about partitioning. It is supposed to be narrow-minded.
>
> Sure, but look at all the confusion we have had just on this list about
> it. We had better state why triggers should be used in place of rules
> _for_ _partitioning_ or that confusion will continue.
Please find enclosed a patch with use cases for each.
Cheers,
David.
--
David Fetter <[EMAIL PROTECTED]> http://fetter.org/
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Index: doc/src/sgml/ddl.sgml
===================================================================
RCS file: /projects/cvsroot/pgsql/doc/src/sgml/ddl.sgml,v
retrieving revision 1.77
diff -c -r1.77 ddl.sgml
*** doc/src/sgml/ddl.sgml 28 Nov 2007 15:42:31 -0000 1.77
--- doc/src/sgml/ddl.sgml 29 Nov 2007 17:51:46 -0000
***************
*** 2510,2564 ****
<listitem>
<para>
If data will be added only to the latest partition, we can
! set up a very simple rule to insert data. We must
! redefine this each month so that it always points to the
! current partition:
!
! <programlisting>
! CREATE OR REPLACE RULE measurement_current_partition AS
! ON INSERT TO measurement
! DO INSTEAD
! INSERT INTO measurement_y2006m01 VALUES ( NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales );
</programlisting>
We might want to insert data and have the server automatically
locate the partition into which the row should be added. We
! could do this with a more complex set of rules as shown below:
<programlisting>
! CREATE RULE measurement_insert_y2004m02 AS
! ON INSERT TO measurement WHERE
! ( logdate >= DATE '2004-02-01' AND logdate < DATE '2004-03-01' )
! DO INSTEAD
! INSERT INTO measurement_y2004m02 VALUES ( NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales );
! ...
! CREATE RULE measurement_insert_y2005m12 AS
! ON INSERT TO measurement WHERE
! ( logdate >= DATE '2005-12-01' AND logdate < DATE '2006-01-01' )
! DO INSTEAD
! INSERT INTO measurement_y2005m12 VALUES ( NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales );
! CREATE RULE measurement_insert_y2006m01 AS
! ON INSERT TO measurement WHERE
! ( logdate >= DATE '2006-01-01' AND logdate < DATE '2006-02-01' )
! DO INSTEAD
! INSERT INTO measurement_y2006m01 VALUES ( NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales );
! </programlisting>
!
! Note that the <literal>WHERE</literal> clause in each rule
! exactly matches the <literal>CHECK</literal>
! constraint for its partition.
</para>
</listitem>
</orderedlist>
--- 2510,2589 ----
<listitem>
<para>
If data will be added only to the latest partition, we can
! set up a very simple trigger function to insert data. We must
! redefine this each month so that it always points to the current
! partition:
!
! <programlisting>
! CREATE OR REPLACE FUNCTION measurement_current_partition()
! RETURNS TRIGGER
! LANGUAGE plpgsql
! AS $$
! BEGIN
! INSERT INTO measurement_y2006m01
! VALUES (
! NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales
! );
! RETURN NEW;
! END;
! $$;
! </programlisting>
!
! The first time we create the table, we create a trigger which
! calls the above trigger function. When we replace the trigger
! function, we don't need to replace the trigger.
!
! <programlisting>
! CREATE TRIGGER insert_measurement_current_partition
! BEFORE INSERT
! ON measurement
! EXECUTE PROCEDURE measurement_current_partition();
</programlisting>
We might want to insert data and have the server automatically
locate the partition into which the row should be added. We
! could do this with a more complex trigger function as shown
! below:
<programlisting>
! CREATE OR REPLACE FUNCTION measurement_insert()
! RETURNS TRIGGER
! LANGUAGE plpgsql
! AS $$
! BEGIN
! IF ( logdate >= DATE '2004-02-01' AND logdate < DATE '2004-03-01' )
THEN
!
! INSERT INTO measurement_y2004m02
! VALUES (
! NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales
! );
! ELSIF ( logdate >= DATE '2005-12-01' AND logdate < DATE
'2006-01-01' ) THEN
! ...
! ELSIF ( logdate >= DATE '2008-01-01' AND logdate < DATE
'2006-02-01' ) THEN
! INSERT INTO measurement_y2008m01
! VALUES (
! NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales
! );
! ELSE
! RAISE EXCEPTION 'In, measurement_insert(), the date out of range.
Fix the trigger function!';
! END IF;
! RETURN NULL;
! END;
! $$;
! </programlisting>
!
! Note that the <literal>WHERE</literal> clause in each section
! of the trigger function exactly matches the
! <literal>CHECK</literal> constraint for its partition.
</para>
</listitem>
</orderedlist>
***************
*** 2568,2594 ****
As we can see, a complex partitioning scheme could require a
substantial amount of DDL. In the above example we would be
creating a new partition each month, so it might be wise to write a
! script that generates the required DDL automatically.
</para>
! <para>
! Partitioning can also be arranged using a <literal>UNION ALL</literal>
! view:
<programlisting>
! CREATE VIEW measurement AS
! SELECT * FROM measurement_y2004m02
! UNION ALL SELECT * FROM measurement_y2004m03
! ...
! UNION ALL SELECT * FROM measurement_y2005m11
! UNION ALL SELECT * FROM measurement_y2005m12
! UNION ALL SELECT * FROM measurement_y2006m01;
</programlisting>
- However, the need to
- recreate the view adds an extra step to adding and dropping
- individual partitions of the data set.
- </para>
</sect2>
<sect2 id="ddl-partitioning-managing-partitions">
--- 2593,2623 ----
As we can see, a complex partitioning scheme could require a
substantial amount of DDL. In the above example we would be
creating a new partition each month, so it might be wise to write a
! script that generates the required DDL automatically. You could
! also write a function to determine the partition dynamically
! before doing the INSERT.
</para>
! <para>
! In the much rarer case where you only plan to do bulk
! inserts--batch inserts of logs would be an example--you can use
! RULEs instead of TRIGGERs. Here is an example of a RULE you
! would change via a cron job at the end of each month:
<programlisting>
! CREATE OR REPLACE RULE measurement_current_partition AS
! ON INSERT TO measurement
! DO INSTEAD
! INSERT INTO measurement_y2008m01
! VALUES (
! NEW.city_id,
! NEW.logdate,
! NEW.peaktemp,
! NEW.unitsales
! );
</programlisting>
+ </para>
</sect2>
<sect2 id="ddl-partitioning-managing-partitions">
***************
*** 2751,2772 ****
<para>
There is currently no way to verify that all of the
<literal>CHECK</literal> constraints are mutually
! exclusive. Care is required by the database designer.
</para>
</listitem>
- <listitem>
- <para>
- There is currently no simple way to specify that rows must not be
- inserted into the master table. A <literal>CHECK (false)</literal>
- constraint on the master table would be inherited by all child
- tables, so that cannot be used for this purpose. One possibility is
- to set up an <literal>ON INSERT</> trigger on the master table that
- always raises an error. (Alternatively, such a trigger could be
- used to redirect the data into the proper child table, instead of
- using a set of rules as suggested above.)
- </para>
- </listitem>
</itemizedlist>
</para>
--- 2780,2791 ----
<para>
There is currently no way to verify that all of the
<literal>CHECK</literal> constraints are mutually
! exclusive. It is easier to create code which generates
! partitions and creates and/or modifies associated objects than
! to write each by hand.
</para>
</listitem>
</itemizedlist>
</para>
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