Re: 9a57858f1103b89a5674f0d50c5fe1f756411df6

Josh Berkus wrote:
> Alvaro, All:
>
> Can someone help me with what we should tell users about this issue?
>
> 1. What users are especially likely to encounter it? All replication
> users, or do they have to do something else?

Replication users are more likely to get it on replicas, of course,
because that's running the recovery code continuously; however, anyone
that suffers a crash of a standalone system might also be affected.
(And it'd be worse, even, because that corrupts your main source of
data, not just a replicated copy of it.) Obviously, if you have a
corrupted replica and fail over to it, you're similarly screwed.

Basically you might be affected if you have tables that are referenced
in primary keys and to which you also apply UPDATEs that are
HOT-enabled.

> 2. What error messages will affected users get? A link to the reports
> of this issue on pgsql lists would tell me this, but I'm not sure
> exactly which error reports are associated.

Not sure about error messages. Essentially some rows would be visible
to seqscans but not to index scans.
These are the threads:
http://www.postgresql.org/message-id/CAM3SWZTMQiCi5PV5OWHb+bYkUcnCk=O67w0cSswPvV7XfUcU5g@mail.gmail.com
http://www.postgresql.org/message-id/CAM-w4HPTOeMT4KP0OJK+mGgzgcTOtLRTvFZyvD0O4aH-7dxo3Q@mail.gmail.com

> 3. If users have already encountered corruption due to the fixed issue,
> what do they need to do after updating? re-basebackup?

Replicas can be fixed by recloning, yeah. I haven't stopped to think
how to fix the masters. Greg, Peter, any clues there?

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services