Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)

public inbox for [email protected]  
help / color / mirror / Atom feed

From: Andrey Borodin <[email protected]>
To: Melanie Plageman <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Robert Haas <[email protected]>
Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)
Date: Mon, 14 Jul 2025 11:37:47 +0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAAKRu_a-aVGxNEdkJt+96HGryQXuQNuXe+PhR0KcnUhXSOPBJw@mail.gmail.com>
References: <CAAKRu_ZMw6Npd_qm2KM+FwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g@mail.gmail.com>
	<CAAKRu_YXP1Us41fkZJeBK5SSj5whNC0C9fZNT6Brdtm+F0agpg@mail.gmail.com>
	<CAAKRu_bAR5uCfjuc06vc_xrZjNCJLs493NgHjTOUDso9qGdE0w@mail.gmail.com>
	<CAAKRu_ac4vUdU-U3ax8j=N8y2OM9-pbFZhafLVfzDOM8MtzvvA@mail.gmail.com>
	<[email protected]>
	<CAAKRu_a-aVGxNEdkJt+96HGryQXuQNuXe+PhR0KcnUhXSOPBJw@mail.gmail.com>

> On 14 Jul 2025, at 00:15, Melanie Plageman <[email protected]> wrote:
> 
>> 
>> Also, I'd prefer "page is not marked all-visible but visibility map bit is set in relation" to emit XX001 for monitoring reasons, but again, this is small note, while I need a broader picture.
> 
> Could you clarify what you mean by this? Are you talking about the
> string representation of the visibility map bits in the WAL record
> representations in heapdesc.c?

This might be a bit off-topic for this thread, but as long as the patch touches that code we can look into this too.

If VM bit all-visible is set while page is not all-visible IndexOnlyScan will show incorrect results. I observed this inconsistency few times on production.

Two persistent subsystems (VM and heap) contradict each other, that's why I think this is a data corruption. Yes, we can repair the VM by assuming heap to be the source of truth in this case. But we must also emit ERRCODE_DATA_CORRUPTED XX001 code into the logs. In many cases this will alert on-call SRE.

To do so I propose to replace elog(WARNING,...) with ereport(WARNING,(errcode(ERRCODE_DATA_CORRUPTED),..).

Best regards, Andrey Borodin.

view thread (143+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected], [email protected]
  Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox