Shared memory leak on DSM slot exhaustion
Hello,
As reported over on pgsql-general[1]/messages/by-id/CA+hUKG+zw87b70yJp+Ozz6LqS6s9QvdO4+hQuZc=DWLMi6Od6A@mail.gmail.com, 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]: /messages/by-id/CA+hUKG+zw87b70yJp+Ozz6LqS6s9QvdO4+hQuZc=DWLMi6Od6A@mail.gmail.com
Attachments:
0001-Fix-memory-leak-on-DSM-slot-exhaustion.patchapplication/octet-stream; name=0001-Fix-memory-leak-on-DSM-slot-exhaustion.patchDownload+8-10
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