Re: CREATE INDEX CONCURRENTLY does not index prepared xact's data

On Tue, Nov 02, 2021 at 06:20:42AM +0530, Sandeep Thakkar wrote:
> (gdb) frame 1
> 
> #1  0x40000000003fdc00:0 in equalTupleDescs (tupdesc1=0x60000000001f65e0,
> 
>     tupdesc2=0x60000000001fba08)
> 
...
> (gdb) p tupdesc2->attrs[2]
> 
> $6 = {attrelid = 27272, attname = {data = "b", '\000' <repeats 62 times>},
>   atttypid = 19, attstattarget = -1, attlen = 64, attnum = 3, attndims = 0,
>   attcacheoff = -1, atttypmod = -1, attbyval = false, attalign = 99 'c',
>   attstorage = 112 'p', attcompression = 0 '\000', attnotnull = false,
>   atthasdef = false, atthasmissing = false, attidentity = 0 '\000',
>   attgenerated = 0 '\000', attisdropped = false, attislocal = true,
>   attinhcount = 0, attcollation = 950}

That looks healthy.  Since gdb isn't giving line numbers, let's single-step
from the start of the function and see if that is informative.  Please apply
the attached patch, which just adds a test file.  Then run "make -C
src/test/subscription check PROVE_TESTS=t/080_step_equalTupleDescs.pl" and
attach
src/test/subscription/tmp_check/log/regress_log_080_step_equalTupleDescs in a
reply to this email.

On Mon, Nov 01, 2021 at 12:01:08AM +0500, Andrey Borodin wrote:
> So far I didn't come up with a clear understanding how this might happen.

Agreed.

> The only idea I have:
> 1. It seems equalTupleDescs() got two valid pointers, probably with broken data.
> 2. Maybe relation->rd_rel (alloceted just before relation->rd_att) was used incorrectly?
> 3. This could happen if CLASS_TUPLE_SIZE is calculated wrong. Don't we need to MAXALIGN everything due to added
sizeof(relminmxid)?
> #define CLASS_TUPLE_SIZE \
>      (offsetof(FormData_pg_class,relminmxid) + sizeof(TransactionId))

See the comment at overread_tuplestruct_pg_cast for the reason why I think
that can't cause an actual malfunction.  Still, there's some possibility of
this being the explanation.