From: Gnanavel Shanmugam <s.gnanavel@inbox.com>
To: David Mitchell <david.mitchell@telogis.com>
To: pgsql-performance@postgresql.org
Subject: Re: How can I speed up this function?
Date: Mon, 27 Jun 2005 20:06:11 -0800
Message-ID: <96ACC448E50.000007FCs.gnanavel@inbox.com> (raw)
In-Reply-To: <42C0B7EE.4040608@telogis.com>
Merge the two select statements like this and try,
SELECT t.trans_id as ID,s.id, s.transaction_id, s.table_name, s.op, s.data
FROM pending_trans AS t join dbmirror.pending_statement AS s
on (s.transaction_id=t.id)
WHERE t.fetched = false order by t.trans_id,s.id limit 100;
If the above query works in the way you want, then you can also do the
update
using the same.
with regards,
S.Gnanavel
> -----Original Message-----
> From: david.mitchell@telogis.com
> Sent: Tue, 28 Jun 2005 14:37:34 +1200
> To: pgsql-performance@postgresql.org
> Subject: [PERFORM] How can I speed up this function?
>
> We have the following function in our home grown mirroring package, but
> it isn't running as fast as we would like. We need to select statements
> from the pending_statement table, and we want to select all the
> statements for a single transaction (pending_trans) in one go (that is,
> we either select all the statements for a transaction, or none of them).
> We select as many blocks of statements as it takes to top the 100
> statement limit (so if the last transaction we pull has enough
> statements to put our count at 110, we'll still take it, but then we're
> done).
>
> Here is our function:
>
> CREATE OR REPLACE FUNCTION dbmirror.get_pending()
> RETURNS SETOF dbmirror.pending_statement AS
> $BODY$
>
> DECLARE
> count INT4;
> transaction RECORD;
> statement dbmirror.pending_statement;
> BEGIN
> count := 0;
>
> FOR transaction IN SELECT t.trans_id as ID
> FROM pending_trans AS t WHERE fetched = false
> ORDER BY trans_id LIMIT 50
> LOOP
> update pending_trans set fetched = true where trans_id =
> transaction.id;
>
> FOR statement IN SELECT s.id, s.transaction_id, s.table_name, s.op,
> s.data
> FROM dbmirror.pending_statement AS s
> WHERE s.transaction_id = transaction.id
> ORDER BY s.id ASC
> LOOP
> count := count + 1;
>
> RETURN NEXT statement;
> END LOOP;
>
> IF count > 100 THEN
> EXIT;
> END IF;
> END LOOP;
>
> RETURN;
> END;$BODY$
> LANGUAGE 'plpgsql' VOLATILE;
>
> Table Schemas:
>
> CREATE TABLE dbmirror.pending_trans
> (
> trans_id oid NOT NULL,
> fetched bool DEFAULT false,
> CONSTRAINT pending_trans_pkey PRIMARY KEY (trans_id)
> )
> WITHOUT OIDS;
>
> CREATE TABLE dbmirror.pending_statement
> (
> id oid NOT NULL DEFAULT nextval('dbmirror.statement_id_seq'::text),
> transaction_id oid NOT NULL,
> table_name text NOT NULL,
> op char NOT NULL,
> data text NOT NULL,
> CONSTRAINT pending_statement_pkey PRIMARY KEY (id)
> )
> WITHOUT OIDS;
>
> CREATE UNIQUE INDEX idx_stmt_tran_id_id
> ON dbmirror.pending_statement
> USING btree
> (transaction_id, id);
>
> Postgres 8.0.1 on Linux.
>
> Any Help would be greatly appreciated.
>
> Regards
>
> --
> David Mitchell
> Software Engineer
> Telogis
>
> ---------------------------(end of broadcast)---------------------------
> TIP 8: explain analyze is your friend
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To: pgsql-performance@postgresql.org
Cc: s.gnanavel@inbox.com, david.mitchell@telogis.com
Subject: Re: How can I speed up this function?
In-Reply-To: <96ACC448E50.000007FCs.gnanavel@inbox.com>
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