Обсуждение: Shared memory leak on DSM slot exhaustion

Hello,

As reported over on pgsql-general[1], we leak shared memory when we
run out of DSM slots.  To see this, add the random-run-out-of-slots
hack I showed in that thread, create and analyze a table t(i) with a
million integers, run with dynamic_shared_memory_type=mmap, and try
SELECT COUNT(*) FROM t t1 JOIN t t2 USING (i) a few times and you'll
see that pgbase/pg_dynshmem fills up with leaked memory segments each
time an out-of-slots errors is raised.  (It happens with all DSM
types, but then the way to list the segments varies or there isn't
one, depending on type and OS.)  Here's a draft patch to fix that.

[1]
https://www.postgresql.org/message-id/CA%2BhUKG%2Bzw87b70yJp%2BOzz6LqS6s9QvdO4%2BhQuZc%3DDWLMi6Od6A%40mail.gmail.com

On Thu, Jan 30, 2020 at 4:54 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> As reported over on pgsql-general[1], we leak shared memory when we
> run out of DSM slots.  To see this, add the random-run-out-of-slots
> hack I showed in that thread, create and analyze a table t(i) with a
> million integers, run with dynamic_shared_memory_type=mmap, and try
> SELECT COUNT(*) FROM t t1 JOIN t t2 USING (i) a few times and you'll
> see that pgbase/pg_dynshmem fills up with leaked memory segments each
> time an out-of-slots errors is raised.  (It happens with all DSM
> types, but then the way to list the segments varies or there isn't
> one, depending on type and OS.)  Here's a draft patch to fix that.

Whoops. The patch looks OK to me.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

On Sat, Feb 1, 2020 at 7:37 AM Robert Haas <robertmhaas@gmail.com> wrote:
> Whoops. The patch looks OK to me.

Pushed.