From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
---|---|
To: | paolo romano <paolo(dot)romano(at)yahoo(dot)it> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: MultiXacts & WAL |
Date: | 2006-06-17 11:05:16 |
Message-ID: | Pine.OSF.4.61.0606171349020.307302@kosh.hut.fi |
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Lists: | pgsql-hackers |
On Sat, 17 Jun 2006, paolo romano wrote:
> When a transaction enters (successfully) the prepared state it only
> retains its exclusive locks and releases any shared locks (i.e.
> multixacts)... or, at least, that's how it should be in principle
> according to serializiaton theory, i haven't yet checked out if this is
> what is done in postgresql .
In PostgreSQL, shared locks are not taken when just reading data. They're
used to enforce foreign key constraints. When inserting a row to a table
with a foreign key, the row in the parent table is locked to
keep another transaction from deleting it. It's not safe to release the
lock before end of transaction.
- Heikki
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