Concurrent read from a partition table.

On Tue, Jul 12, 2011 at 6:01 AM, hyelluas <helen_yelluas@mcafee.com> wrote:

Hello,

I’m having a problem with concurrent processing.
2 queries are accessing the same parent table that have 24 partitions.
I see “shared lock is not granted “ for one of them on one of the children
while the other query is running.

Does the “ select from a parent table” make a lock on the children?

In general if there are no predicates in query, then select would be fired
across all
children.

How I can change it?
The one of the queries runs hourly ( 8 min) on the server , the other one
can be run by a user , and a few users can run the same query.

Thank you.
Helen

Could you post a self-contained test case?

Regards,
Chetan

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Hi Chetan,

I'm not sure how I can create a test case, I'm running queryes on 50g of
data to see this.

My general questions are about locking children when select from a parent, I
have not seen any documentation on it. Does any parameter like 'concurrent
read' exist? I'm still new to postgres, came from oracle & mysql.

Thanks.
Helen

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On Tue, Jul 12, 2011 at 11:46 PM, hyelluas <helen_yelluas@mcafee.com> wrote:

Hi Chetan,

I'm not sure how I can create a test case, I'm running queryes on 50g of
data to see this.

My general questions are about locking children when select from a parent,
I
have not seen any documentation on it. Does any parameter like 'concurrent
read' exist? I'm still new to postgres, came from oracle & mysql.

Thanks.
Helen

I tried with the attached test case and found that both the tables - base as
well as child tables are locked in shared mode for select queries.
For details, please check the attached inheritance_locks.txt file.

With "concurrent read" did you mean isolation settings?
Then please refer:
http://www.postgresql.org/docs/9.0/static/sql-set-transaction.html

Regards,
Chetan

--
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

Website: www.enterprisedb.com
EnterpriseDB Blog : http://blogs.enterprisedb.com
Follow us on Twitter : http://www.twitter.com/enterprisedb