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Re: [HACKERS] table partitioning pl/pgsql helpers

From: Jim Nasby <decibel(at)decibel(dot)org>
To: Enrico Sirola <enrico(dot)sirola(at)gmail(dot)com>
Cc: "pgsql-general(at)postgresql(dot)org General" <pgsql-general(at)postgresql(dot)org>
Subject: Re: [HACKERS] table partitioning pl/pgsql helpers
Date: 2007-06-01 22:53:56
Message-ID: F1465A3F-4136-4050-B486-1CE0FDE69429@decibel.org (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
Dropping -hackers; that list is for development of the database  
engine itself.

The problem is that rules will happen before triggers, so what you're  
trying to do will never work. Instead, just have the trigger insert  
the data into the appropriate table.

On May 30, 2007, at 9:55 AM, Enrico Sirola wrote:

> Hello,
>
> I'm trying to write a trigger on insert which should insert the row  
> in another
> table. The table on which to insert the row should be selected at  
> runtime and
> it is not know in advance. For example, let's say we have a table with
> two columns, a date and an integer. a row is inserted into table  
> XXX and
>
> CREATE TABLE XXX
> (
> 	refdate date;
> 	x2 integer;
> )
>
> when the statement
>
> insert into XXX VALUES ('2007-11-11', 1);
>
> is executed, a trigger (or rule) should be fired to insert the row  
> into
> table XXX_20071111 (having the same schema). If the XXX_* tables  
> are created beforehand
> this is not a problem because you can set up a rule for each date  
> performing
> the needed insert (as documented in http://www.postgresql.org/docs/ 
> 8.1/interactive/ddl-partitioning.html)
>
> The problem arises when you try to extend the trigger in order to  
> also dinamically
> perform table creation is the XXX_20071111 doesn't exist:
>
> I have, for example:
>
>
> CREATE OR REPLACE FUNCTION add_child_table(parent_name varchar, d  
> date)
> RETURNS varchar AS $$
> DECLARE
>         new_table_name varchar;
> BEGIN
>       raise notice '%', 'creating table';
>         new_table_name := date2tblname(parent_name, d); -- converts  
> table name and date into child table name
>         execute 'CREATE TABLE ' || new_table_name || ' ( ) INHERITS  
> (' || parent_name || ')';
>         execute 'CREATE RULE '
>                 || new_table_name
>                 || '_insert AS ON INSERT TO '
>                 || parent_name
>                 || ' WHERE ( refdate = DATE ' /* refdate is the  
> field we use to partition */
>                 || '''' || d || ''''
>                 || ' ) DO INSTEAD INSERT INTO '
>                 || new_table_name
>                 || ' VALUES ( NEW.* )';
>         return new_table_name;
> END;
> $$ LANGUAGE plpgsql;
>
> I can use the above to add a child table and the rule to implement  
> partitioning
>
> CREATE OR REPLACE FUNCTION child_creation_trigger()
> RETURNS "trigger" AS $$
> BEGIN
>         IF ( child_exist(TG_RELNAME::text, NEW.refdate) = false ) THEN
>               raise notice '%', 'creating ' || TG_RELNAME::text ||  
> ' for ' || NEW.refdate::text;
>               perform add_child_table(TG_RELNAME::text, NEW.refdate);
>               --insert into ' || child_table_name || ' values  
> ( NEW.* );
>               RETURN NEW;
>         ELSE
>               raise notice '%', 'NOT creating ' || TG_RELNAME::text  
> || ' for ' || NEW.refdate::text;
>               RETURN NEW;
>         END IF;
> END;
> $$ LANGUAGE plpgsql;
>
> The trigger function is hooked to the to-be-partitioned table
>
>
> CREATE TRIGGER XXX_trigger BEFORE INSERT
> ON XXX FOR EACH ROW
> execute procedure child_creation_trigger ();
>
>
> now, every time I insert a tuple into XXX, the trigger is fired and  
> checks if the needed table exists or
> not. If not, it creates the table and rule and goes on. The problem  
> is that in this case the first
> row is inserted into the XXX table, not in the (just created)  
> XXX_<refdate> . Then I tried to insert
> the row myself from the trigger body (and return null in order to  
> skip the original insertion), but
> I'm not able to do it (see the commented insert in the above IF  
> clause) because I can't properly
> quote the target table name.
> I shoud perform a
>
> insert into child_table_name values (NEW.*);
>
> obviously written like this the plpgsql complains at runtime  
> because child_table_name is not a table name.
> If, on the other side, I dynamically create the query like in
>
> execute 'insert into ' || child_table_name || ' values (NEW.*)';
>
> it complains because NEW in the execution context is unknown.
>
> This should be a rather common problem... Isn't it? Is there a  
> canonical way to
> solve it? Maybe there's a trivial answer, but I have no plpgsql  
> programming
> experience.
>
> Thanks a lot in advance,
>
> Enrico Sirola
> enrico(dot)sirola(at)gmail(dot)com
>
>
>

--
Jim Nasby                                            jim(at)nasby(dot)net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)



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