[PATCH] Compressed TOAST data corruption with REPACK CONCURRENTLY

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