Re: Parallel scan with SubTransGetTopmostTransaction assert coredump

On Tue, May 11, 2021 at 11:28 AM Pengchengliu <pengchengliu@tju.edu.cn> wrote:
>
> Hi Andres,
>    Reproduce steps.
>
> 1, Modify and adjust NUM_SUBTRANS_BUFFERS to 128 from 32 in the file  "src/include/access/subtrans.h" line number 15.
> 2, configure with enable assert and build it.
> 3, init a new database cluster.
> 4, modify  postgres.conf  and add some parameters as below. As the coredump from parallel scan, so we adjust parallel setting, make it easy to reproduce.
>
>   max_connections = 2000
>
>   parallel_setup_cost=0
>   parallel_tuple_cost=0
>   min_parallel_table_scan_size=0
>   max_parallel_workers_per_gather=8
>   max_parallel_workers = 32
>
> 5, start the database cluster.
> 6, use the script init_test.sql  in attachment to create tables.
> 7, use pgbench with script sub_120.sql in attachment to test it. Try it sometimes, you should get the coredump file.
>     pgbench  -d postgres -p 33550  -n -r -f sub_120.sql   -c 200 -j 200 -T 120
>

Hi,

I had a go at reproducing your reported issue, making sure to follow
all your steps.
Unfortunately, your script seemed to run OK with pgbench and no
crash/coredump occurred for me (and yes, I definitely had asserts
enabled).
I tried with both the 13.2 source code
(3fb4c75e857adee3da4386e947ba58a75f3e74b7), running through the script
with pgbench twice to completion, and also did the same using the
latest Postgres source code.

Will be interesting to see if anyone is able to reproduce your issue.

Regards,
Greg Nancarrow
Fujitsu Australia