Re: All-visible pages with valid prune xid are confusing

From: Melanie Plageman <melanieplageman(at)gmail(dot)com>
To: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de>
Subject: Re: All-visible pages with valid prune xid are confusing
Date: 2025-12-02 18:23:57
Message-ID: CAAKRu_YmOFcg3jTc+q6jB1eTq6txpnkwORF44SKXwDqCQZW3ZQ@mail.gmail.com
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On Tue, Dec 2, 2025 at 12:49 PM Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>
> Hmm. If the page has no prunable tuples left, it makes sense to set
> pd_prune_xid to InvalidTransactionId to avoid the useless round of
> pruning. In other cases, it would make sense to set it to some XID so
> that it gets pruned later. But a standby will only start pruning if it's
> later promoted to become a primary. At that point, all currently running
> transactions will be finished (except for prepared transactions).

What about on-access pruning during SELECT queries on a hot standby?

- Melanie

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