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help / color / mirror / Atom feedFrom: Nico Heller <[email protected]>
To: Tom Lane <[email protected]>
Cc: [email protected]
Subject: Re: Guarantee order of batched pg_advisory_xact_lock
Date: Thu, 12 Feb 2026 11:18:34 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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I just checked for hash collisions with the following query today:
SELECT COUNT(*), hashtextextended(key, 0) FROM
(
SELECT key FROM table1
UNION
SELECT key FROM table2
UNION
...
) keys (key)
GROUP BY hashtextextended(key, 0)
HAVING COUNT(*) > 1
Where table1, table2, ... are all the tables we are acquire keys from to
use for the mentioned query.
Sadly, no results were returned. Thus, I can rule out hash collisions.
Any other thoughts? Here is an error log from the JDBC driver:
org.postgresql.util.PSQLException: ERROR: deadlock detected Detail:
Process 60780 waits for ExclusiveLock on advisory lock
[24605,3030106527,494580150,1]; blocked by process 65280.
Process 65280 waits for ExclusiveLock on advisory lock
[24605,1321834016,1311356115,1]; blocked by process 60780.
On 2/11/26 23:49, Tom Lane wrote:
> Nico Heller<[email protected]> writes:
>> So it would probably be better to ORDER BY the hashtextended result
>> instead of :keysToLock, right?
> Yeah, that seems like it'd work, if you have no other dependencies
> on the locking order.
>
> regards, tom lane
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