Re: GiST index build missing smgrimmedsync()?

Heikki Linnakangas <hlinnaka@iki.fi>

From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Melanie Plageman <melanieplageman@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2022-02-24T14:32:53Z
Lists: pgsql-hackers
On 23/02/2022 23:30, Melanie Plageman wrote:
> I brought this up in [1] but wanted to start a dedicated thread.
> 
> Since 16fa9b2b30a357 GiST indexes are not built in shared buffers.
> However, smgrimmedsync() is not done anywhere and skipFsync=true is
> always passed to smgrwrite() and smgrextend(). So, if a checkpoint
> starts and finishes after WAL-logging some of the index build pages and
> there is a crash sometime before the dirty pages make it to permanent
> storage, won't that data be lost?

Yes, good catch!

> Seems like the following would address this:

Committed essentially that, except that I put the smgrimmedsync in a 
separate if-block, and copied the comment from the similar piece of code 
from nbtsort.c to explain the issue.

Thanks!

- Heikki



Commits

  1. Fix data loss on crash after sorted GiST index build.