Obtaining advisory lock using ORDER BY

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От	Andreas Joseph Krogh
Тема	Obtaining advisory lock using ORDER BY
Дата	13 июля 2015 г. 14:15:50
Msg-id	VisenaEmail.d6.3439608014f9803b.14e87beacbf@tc7-visena обсуждение исходный текст
Ответы	Re: Obtaining advisory lock using ORDER BY
Список	pgsql-general

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Hi all.

I have this "dequeue" query which is working:

select qe.entity_id, qe.queue_id, qe.sequence_id, qe.tx_id    , qe.payload_string
from origo_queue_entry qe
WHERE
    qe.queue_id = 2
    AND pg_try_advisory_xact_lock(sequence_id)
LIMIT 1 FOR UPDATE
;

I'm not sure is this is guaranteed to lock in ASC-order on column sequence_id, is it?

To ensure this I've tried with an explicit ORDER BY on "sequence_id", like this:

select qe.entity_id, qe.queue_id, qe.sequence_id, qe.tx_id    , qe.payload_string
from origo_queue_entry qe
WHERE
    qe.queue_id = 2
    AND pg_try_advisory_xact_lock(sequence_id)
ORDER BY qe.sequence_id ASC LIMIT 1 FOR UPDATE
;