On Tue, Jul 9, 2019 at 11:11 PM Konstantin Malanchev <hom...@gmail.com> wrote: > Thank you for explanation. work_mem = 512MB and > max_parallel_workers_per_gather = 2 and I run only one Postgres instance and > only one query. EXPLAIN shows "Workers Planned: 2" for this query. Why it can > use more than 1GB of /dev/shm?
For example, if you have one Parallel Hash Join in your plan, it could allocate up to 512MB * 3 of shared memory (3 = leader process + 2 workers). It sounds like you'll need to set work_mem smaller. If you run EXPLAIN ANALYZE you'll see how much memory is used by individual operations. Usually it's regular private anonymous memory, but for Parallel Hash it's /dev/shm memory. -- Thomas Munro https://enterprisedb.com
