Re: [HACKERS] Parallel Hash take II

Hi Thomas,

I was testing this feature with v20 patch, and I got a crash while doing large joins with small work_mem, and lots of workers as below.

-- Machine Configuration: (d1.xlarge) CUPs : 8 , RAM  : 16GB , SIze : 640GB

-- postgres.conf setting as below:
work_mem = 64kB
max_parallel_workers_per_gather = 128
max_parallel_workers = 64
enable_mergejoin = off
enable_nestloop = off
enable_hashjoin = on
force_parallel_mode = on
seq_page_cost = 0.1
random_page_cost = 0.1
effective_cache_size = 128MB
parallel_tuple_cost = 0
parallel_setup_cost = 0
parallel_synchronization_cost = 0

-- created only one table "lineitem" of size 93GB.
postgres=# select pg_size_pretty(pg_total_relation_size('lineitem'));
 pg_size_pretty
----------------
 93 GB
(1 row)

[centos@centos-prabhat bin]$ vi test10.sql
explain (analyze, costs off)
select  count(*) from lineitem t1 join lineitem t2 using(l_suppkey) join lineitem t3 using(l_suppkey);
select  count(*) from lineitem t1 join lineitem t2 using(l_suppkey) join lineitem t3 using(l_suppkey);

[centos@centos-prabhat bin]$ ./psql postgres -a -f test10.sql > test10.out

[centos@centos-prabhat bin]$ vi test10.out
explain (analyze, costs off)
select  count(*) from lineitem t1 join lineitem t2 using(l_suppkey) join lineitem t3 using(l_suppkey);
psql:test10.sql:2: WARNING:  terminating connection because of crash of another server process
DETAIL:  The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
HINT:  In a moment you should be able to reconnect to the database and repeat your command.
psql:test10.sql:2: server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
psql:test10.sql:2: connection to server was lost


Kindly check, if you can reproduce the same at your end.