| Lists: | pgsql-sql |
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| From: | "Denis Khabas" <dkhabas(at)bluecatnetworks(dot)com> |
|---|---|
| To: | <pgsql-sql(at)postgresql(dot)org> |
| Subject: | Which SQL command creates ExclusiveLock? |
| Date: | 2004-04-21 14:58:28 |
| Message-ID: | 5DEC3FFCDE2F7C4DA45433EE09A4F22C013457FF@colossus.dyadem.corp |
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| Lists: | pgsql-sql |
Hi everyone!
I have a web application that uses Postgresql on backend. The application performs selects, updates, inserts, and deletes by using Hibernate. Tables
contain indexed fields. When I run the following query, SELECT * FROM pg_locks, it shows that some transactions place
ExclusiveLock:
relation | database | transaction | pid | mode | granted
----------+----------+-------------+-------+-----------------+---------
16757 | 16976 | | 22770 | AccessShareLock | t
| | 17965163 | 22770 | ExclusiveLock | t
According to postgres documentation, all update operations place ROW EXCLUSIVE MODE locks, and
EXCLUSIVE MODE is not automatically acquired by any postgres SQL command. So, which command places
ExclusiveLock??? I suspect that indexes can account for this behaviour, but couldn't find anything in the docs.
I am also wondering why there is nothing shown in "relation" column. I think it is supposed to display a table or index id or any other
object that is being locked.
Thanks for help!
Dennis
| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Denis Khabas" <dkhabas(at)bluecatnetworks(dot)com> |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: Which SQL command creates ExclusiveLock? |
| Date: | 2004-04-28 04:16:28 |
| Message-ID: | 22918.1083125788@sss.pgh.pa.us |
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| Lists: | pgsql-sql |
"Denis Khabas" <dkhabas(at)bluecatnetworks(dot)com> writes:
> According to postgres documentation, all update operations place ROW EXCLUS=
> IVE MODE locks, and=20
> EXCLUSIVE MODE is not automatically acquired by any postgres SQL command. S=
> o, which command places
> ExclusiveLock?
It says that no SQL command acquires ExclusiveLock *on a table*. The
pg_locks row you show represents ExclusiveLock on a transaction number.
Every transaction gets ExclusiveLock on its transaction number for the
duration of its existence.
regards, tom lane