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

> On Apr 16, 2026, at 14:13, SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com> wrote:
> 
> Hi hackers,
> 
> 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.
> 
> Thanks,
> Satya
> <0001-Fix-restore_tuple-losing-varlena-compression-flag.patch><0002-Add-compressed-TOAST-test-to-repack_toast.patch>

I managed to reproduce the bug manually, and confirmed your fix to work for me. The repro is not simple, so I won’t put it here. If somebody is interested in it, then I can provide.

I didn’t review the test in 0002, I guess we don’t have to add the test because once fixed, the bug won’t be there anymore, thus it’s not worthy extending the test time.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/