Re: [PATCH] Compressed TOAST data corruption with REPACK CONCURRENTLY

SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com> wrote:

> restore_tuple() in repack.c uses SET_VARSIZE() to reconstruct the varlena header when 
> reading back external attributes from the spill file. In this process, looks like the flag 
> SET_VARSIZE_COMPRESSED is silently lost. Because of this, when REPACK CONCURRENTLY
> run  any concurrently updated column whose value was TOAST-compressed ends up with raw 
> compressed bytes behind an "uncompressed" header returning garbled data on subsequent reads.
> It appears that existing tests are using random chars which are uncompressable.
> 
> Please find the attached 0001-Fix-restore_tuple-losing-varlena-compression-flag.patch to fix this. 
> Additionally I updated the existing repack_toast test to include the scenario I was talking about.

Good catch, thanks!

I'd slightly prefer to fix it w/o checking the varlena type, as
attached. However, your test fails to reproduce the issue here, so I'm not
able to verify the fix. I'll take a closer look early next week.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com