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

[David Mitchell]

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

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