|From:||Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>|
|To:||Andres Freund <andres(at)anarazel(dot)de>|
|Cc:||Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: recovering from "found xmin ... from before relfrozenxid ..."|
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On 2020-Jul-13, Andres Freund wrote:
> On 2020-07-13 17:12:18 -0400, Robert Haas wrote:
> > 1. There's nothing to identify the tuple that has the problem, and no
> > way to know how many more of them there might be. Back-patching
> > b61d161c146328ae6ba9ed937862d66e5c8b035a would help with the first
> > part of this.
> Not fully, I'm afraid. Afaict it doesn't currently tell you the item
> pointer offset, just the block numer, right? We probably should extend
> it to also include the offset...
Just having the block number is already a tremendous step forward; with
that you can ask the customer to set a pageinspect dump of tuple
headers, and then the problem is obvious. Now if you want to add block
number to that, by all means do so.
FWIW I do support the idea of backpatching the vacuum errcontext commit.
One useful thing to do is to mark a tuple frozen unconditionally if it's
marked hinted XMIN_COMMITTED; no need to consult pg_clog in that case.
The attached (for 9.6) does that; IIRC it would have helped in a couple
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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