On 6-Dec-06, at 8:20 AM, Jens Schipkowski wrote:
On Wed, 06 Dec 2006 13:29:37 +0100, Dave Cramer <pg@xxxxxxxxxxxxx>
wrote:
Unless you specifically ask for it postgresql doesn't lock any
rows when you update data.
Thats not right. UPDATE will force a RowExclusiveLock to rows
matching the WHERE clause, or all if no one is specified.
@Joost Kraaijeveld: Yes, because there is no EntryExclusiveLock or
something like that. Roughly you can say, each UPDATE statement
iterates through the affected table and locks the WHERE clause
matching records (rows) exclusivly to prevent data inconsistancy
during the UPDATE. After that your rows will be updated and the
lock will be repealed.
You can see this during an long lasting UPDATE by querying the
pg_locks with joined pg_stats_activity (statement must be enabled).
Apparently I've completely misunderstood MVCC then.... My
understanding is that unless you do a select ... for update then
update the rows will not be locked .
Dave
Dave
On 6-Dec-06, at 2:04 AM, Joost Kraaijeveld wrote:
Does PostgreSQL lock the entire row in a table if I update only 1
column?
--Groeten,
Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
web: www.askesis.nl
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TIP 9: In versions below 8.0, the planner will ignore your desire to
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CU,
Jens
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Jens Schipkowski
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