Reg: BULK COLLECT

On 05/25/2015 07:24 AM, Medhavi Mahansaria wrote:

Hello,

I am porting my application from Oracle to PostgreSQL.

We are using BULK COLLECT functionality of oracle.
How can i change the 'BULK COLLECT' fetch of the data from the cursor to make if compatible for pg/plsql?

A small example is as below (This is just an example and the query is much more complex which returns huge amount of data)

*/CREATE OR REPLACE FUNCTION abc() RETURNS VOID AS $body$/*

*/DECLARE/*
*/l_data b%ROWTYPE;/*

*/POPULATE_STATS CURSOR IS/*
*/(/*
*/SELECT * from a/*
*/)/*
*/; // query returning a huge amount of data/*

*/BEGIN/*
*/ OPEN POPULATE_STATS;/*
*/ LOOP/*
*/ FETCH POPULATE_STATS BULK COLLECT INTO l_data LIMIT 1000;/*
*/ IF POPULATE_STATS%ROWCOUNT > 0/*
*/ THEN/*
*/ FORALL i IN 1..l_data.COUNT/*
*/ INSERT INTO b VALUES l_data(i);/*
*/ END IF;/*
*/ IF NOT FOUND THEN EXIT; END IF; /*
*/ END LOOP;/*
*/ CLOSE POPULATE_STATS;/*
*/EXCEPTION/*
*/ WHEN OTHERS THEN/*
*/ CODE := SQLSTATE;/*
*/ MSG := SQLERRM;/*
*/ INSERT INTO tracker VALUES (CODE,MSG,LOCALTIMESTAMP);/*
*/ RAISE NOTICE 'SQLERRM';/*
*/ RAISE NOTICE '%', SQLSTATE;/*
*/ RAISE NOTICE '%', MSG;/*
*/END;
/*
*/$body$/*
*/LANGUAGE PLPGSQL;/*

How can i change the 'BULK COLLECT' fetch of the data from the cursor to make if compatible for pg/plsql?

Thanks & Regards
Medhavi Mahansaria
Mailto: medhavi.mahansaria@tcs.com

That seems pretty over complicated version of:

insert into b select * from a;

Which is all you'll need in PG. It it does something else, then I failed to understand the stored proc.

-Andy

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It seems you are fetching from a table then sequentially inserting each
record to another table.
In PostgreSQL, you could use cursors in PL/pgSQL ("
http://www.postgresql.org/docs/9.4/interactive/plpgsql-cursors.html").

Alternatively you may write a single query which selects from the table and
performs an insert into the other table, it is usually more efficient than
sequential single record inserts.

If the amount of data are significant you may use ORDER BY and LIMIT in
your SELECT query in order to limit the count of records you are fetching
for insertion.
You may place this SQL query in a loop within a bash script as shown below,
this bash script and the pseudo query updates a few records of a given
table at a time, you may convert this example into an INSERT query for
piecemeal inserts keeping the transaction size manageable.

#!/bin/sh
#date;time sh scripts/sample_piecemeal_db_updation.sh 10000 2>&1|tee
/tmp/sample_piecemeal_db_updation.sh.sh.log;date;
export PSQL_PATH="/apps/postgreSQL/pgsql-9.1.4/bin/psql";
export DB_NAME="my_db";
export PGPORT="5432";
export DB_USER="some_user";
export DB_HOST="some_ip"; #put the actual ip here.
step=$1;

echo `date +%Y-%m-%d.%H%Mhrs:%S.%N`'-DB update commences';
trim() { echo $1; }

_sql_query2="
SELECT count(a.*)AS cnt FROM main_table a;
";
echo $_sql_query2;
counter=0;
for cnt in `$PSQL_PATH -d$DB_NAME -U$DB_USER --port=$PGPORT
--host=$DB_HOST --quiet --tuples-only -c"$_sql_query2"`
do
echo '$cnt is:'$cnt;
counter=$(( $counter + 1 ));
for i in $(seq 0 $step $cnt)
do
_sql_query1="
SET work_mem='1GB';
UPDATE main_table b
SET some_field=a.some_field
FROM
(
SELECT
a.id
,b.some_field2
FROM
(
SELECT
a.*
FROM
main_table a
ORDER BY a.id ASC
OFFSET $i
LIMIT $step
)a
JOIN
some_other_table b
ON
b.some_other_field=a.some_other_field
)a
WHERE
b.id=a.id
;
";
#echo "_sql_query1 is:$_sql_query1";
results=`$PSQL_PATH -d$DB_NAME -U$DB_USER --port=$PGPORT
--host=$DB_HOST --quiet --tuples-only -c"$_sql_query1"`
echo "cnt is:$cnt, step is:$step, i is:$i,
results:$results";
done;
done;
echo `date +%Y-%m-%d.%H%Mhrs:%S.%N`'-DB updation concludes.';

Regards,
Allan.

On Mon, May 25, 2015 at 3:24 PM, Medhavi Mahansaria <
medhavi.mahansaria@tcs.com> wrote:

On 05/25/2015 05:24 AM, Medhavi Mahansaria wrote:

Hello,

I am porting my application from Oracle to PostgreSQL.

We are using BULK COLLECT functionality of oracle.
How can i change the 'BULK COLLECT' fetch of the data from the cursor to
make if compatible for pg/plsql?

See here:

http://www.postgresql.org/docs/9.4/interactive/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING

A small example is as below (This is just an example and the query is
much more complex which returns huge amount of data)

*/CREATE OR REPLACE FUNCTION abc() RETURNS VOID AS $body$/*

*/DECLARE/*
*/l_data b%ROWTYPE;/*

*/POPULATE_STATS CURSOR IS/*
*/(/*
*/SELECT * from a/*
*/)/*
*/; // query returning a huge amount of data/*

*/BEGIN/*
*/ OPEN POPULATE_STATS;/*
*/ LOOP/*
*/ FETCH POPULATE_STATS BULK COLLECT INTO l_data LIMIT 1000;/*
*/ IF POPULATE_STATS%ROWCOUNT > 0/*
*/ THEN/*
*/ FORALL i IN 1..l_data.COUNT/*
*/ INSERT INTO b VALUES l_data(i);/*
*/ END IF;/*
*/ IF NOT FOUND THEN EXIT; END IF; /*
*/ END LOOP;/*
*/ CLOSE POPULATE_STATS;/*
*/EXCEPTION/*
*/ WHEN OTHERS THEN/*
*/ CODE := SQLSTATE;/*
*/ MSG := SQLERRM;/*
*/ INSERT INTO tracker VALUES (CODE,MSG,LOCALTIMESTAMP);/*
*/ RAISE NOTICE 'SQLERRM';/*
*/ RAISE NOTICE '%', SQLSTATE;/*
*/ RAISE NOTICE '%', MSG;/*
*/END;
/*
*/$body$/*
*/LANGUAGE PLPGSQL;/*

How can i change the 'BULK COLLECT' fetch of the data from the cursor to
make if compatible for pg/plsql?

Thanks & Regards
Medhavi Mahansaria
Mailto: medhavi.mahansaria@tcs.com

--
Adrian Klaver
adrian.klaver@aklaver.com

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Dear Andy,

We are using bulk collect to enhance the performance as the data is huge.

But as you said it is ideally insert into b select * from a;

So now I am using the looping through query result option as Adrian
suggested.

http://www.postgresql.org/docs/9.4/interactive/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING

Thank You Adrian.

Thanks & Regards
Medhavi Mahansaria
Tata Consultancy Services Limited
Unit-VI, No.78, 79& 83,
L-Centre, EPIP Industrial Estate,
Whitefield
Bangalore - 560066,Karnataka
India
Ph:- +91 80 67253769
Cell:- +91 9620053040
Mailto: medhavi.mahansaria@tcs.com
Website: http://www.tcs.com
____________________________________________
Experience certainty. IT Services
Business Solutions
Consulting
____________________________________________

From: Andy Colson <andy@squeakycode.net>
To: Medhavi Mahansaria <medhavi.mahansaria@tcs.com>,
pgsql-general@postgresql.org
Date: 05/25/2015 06:15 PM
Subject: Re: [GENERAL] Reg: BULK COLLECT

On 05/25/2015 07:24 AM, Medhavi Mahansaria wrote:

Hello,

I am porting my application from Oracle to PostgreSQL.

We are using BULK COLLECT functionality of oracle.
How can i change the 'BULK COLLECT' fetch of the data from the cursor to

make if compatible for pg/plsql?

A small example is as below (This is just an example and the query is

much more complex which returns huge amount of data)

*/CREATE OR REPLACE FUNCTION abc() RETURNS VOID AS $body$/*

*/DECLARE/*
*/l_data b%ROWTYPE;/*

*/POPULATE_STATS CURSOR IS/*
*/(/*
*/SELECT * from a/*
*/)/*
*/; // query returning a huge amount of data/*

*/BEGIN/*
*/ OPEN POPULATE_STATS;/*
*/ LOOP/*
*/ FETCH POPULATE_STATS BULK COLLECT INTO l_data LIMIT 1000;/*
*/ IF POPULATE_STATS%ROWCOUNT > 0/*
*/ THEN/*
*/ FORALL i IN 1..l_data.COUNT/*
*/ INSERT INTO b VALUES l_data(i);/*
*/ END IF;/*
*/ IF NOT FOUND THEN EXIT; END IF; /*
*/ END LOOP;/*
*/ CLOSE POPULATE_STATS;/*
*/EXCEPTION/*
*/ WHEN OTHERS THEN/*
*/ CODE := SQLSTATE;/*
*/ MSG := SQLERRM;/*
*/ INSERT INTO tracker VALUES (CODE,MSG,LOCALTIMESTAMP);/*
*/ RAISE NOTICE 'SQLERRM';/*
*/ RAISE NOTICE '%', SQLSTATE;/*
*/ RAISE NOTICE '%', MSG;/*
*/END;
/*
*/$body$/*
*/LANGUAGE PLPGSQL;/*

How can i change the 'BULK COLLECT' fetch of the data from the cursor to

make if compatible for pg/plsql?

Thanks & Regards
Medhavi Mahansaria
Mailto: medhavi.mahansaria@tcs.com

That seems pretty over complicated version of:

insert into b select * from a;

Which is all you'll need in PG. It it does something else, then I failed
to understand the stored proc.

-Andy

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On 05/25/2015 07:24 AM, Medhavi Mahansaria wrote:

Hello,

I am porting my application from Oracle to PostgreSQL.

We are using BULK COLLECT functionality of oracle.
How can i change the 'BULK COLLECT' fetch of the data from the cursor

to make if compatible for pg/plsql?

A small example is as below (This is just an example and the query is

much more complex which returns huge amount of data)

*/CREATE OR REPLACE FUNCTION abc() RETURNS VOID AS $body$/*

*/DECLARE/*
*/l_data b%ROWTYPE;/*

*/POPULATE_STATS CURSOR IS/*
*/(/*
*/SELECT * from a/*
*/)/*
*/; // query returning a huge amount of data/*

*/BEGIN/*
*/ OPEN POPULATE_STATS;/*
*/ LOOP/*
*/ FETCH POPULATE_STATS BULK COLLECT INTO l_data LIMIT 1000;/*
*/ IF POPULATE_STATS%ROWCOUNT > 0/*
*/ THEN/*
*/ FORALL i IN 1..l_data.COUNT/*
*/ INSERT INTO b VALUES l_data(i);/*
*/ END IF;/*
*/ IF NOT FOUND THEN EXIT; END IF; /*
*/ END LOOP;/*
*/ CLOSE POPULATE_STATS;/*
*/EXCEPTION/*
*/ WHEN OTHERS THEN/*
*/ CODE := SQLSTATE;/*
*/ MSG := SQLERRM;/*
*/ INSERT INTO tracker VALUES (CODE,MSG,LOCALTIMESTAMP);/*
*/ RAISE NOTICE 'SQLERRM';/*
*/ RAISE NOTICE '%', SQLSTATE;/*
*/ RAISE NOTICE '%', MSG;/*
*/END;
/*
*/$body$/*
*/LANGUAGE PLPGSQL;/*

How can i change the 'BULK COLLECT' fetch of the data from the cursor

to make if compatible for pg/plsql?

Thanks & Regards
Medhavi Mahansaria
Mailto: medhavi.mahansaria@tcs.com

That seems pretty over complicated version of:

insert into b select * from a;

Which is all you'll need in PG. It it does something else, then I
failed to understand the stored proc.

-Andy

On 5/27/2015 12:52 AM, Medhavi Mahansaria wrote:> Dear Andy,

We are using bulk collect to enhance the performance as the data is huge.

But as you said it is ideally insert into b select * from a;

So now I am using the looping through query result option as Adrian
suggested.

http://www.postgresql.org/docs/9.4/interactive/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING

Thank You Adrian.

Thanks & Regards
Medhavi Mahansaria

Did you time it? I'll bet "insert into b select * from a" is the
fastest method.

-Andy

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On 27 May 2015 at 06:52, Medhavi Mahansaria <medhavi.mahansaria@tcs.com>
wrote:

We are using bulk collect to enhance the performance as the data is huge.

Using BULK COLLECT speeds up retrieving rows into memory, but if the data
is huge that wasn't a great plan anyway, so doing it faster doesn't matter
much.

--
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