Re: [PERFORM] How can I speed up this function?

[David Mitchell]

The function I have exits the loop when the count hits 100 yes, but the 
inner loop can push the count up as high as necessary to select all the 
statements for a transaction, so by the time it exits, the count could 
be much higher. I do want to limit the statements, but I want to get 
enough for complete transactions.

David
Gnanavel Shanmugam wrote:
But in the function you are exiting the loop when the count hits 100. If you
do not want to limit the statements then remove the limit clause from the
query I've written.

with regards,
S.Gnanavel



-----Original Message-----
From: [EMAIL PROTECTED]
Sent: Tue, 28 Jun 2005 16:29:32 +1200
To: [EMAIL PROTECTED]
Subject: Re: [PERFORM] How can I speed up this function?

Hi Gnanavel,

Thanks, but that will only return at most 100 statements. If there is a
transaction with 110 statements then this will not return all the
statements for that transaction. We need to make sure that the function
returns all the statements for a transaction.

Cheers

David

Gnanavel Shanmugam wrote:

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: [EMAIL PROTECTED]
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


--
David Mitchell
Software Engineer
Telogis


--
David Mitchell
Software Engineer
Telogis

---------------------------(end of broadcast)---------------------------
TIP 8: explain analyze is your friend