Re: PGSQL 11.4: shared_buffers and /dev/shm size

Hello Jean,

I have 8 GB RAM and /dev/shm size is 4GB, and there is no significant memory usage by other system processes. I surprised that Postgres uses more space in /dev/shm than sharred_buffers parameter allows, probably I don't understand what this parameter means.

I have no opportunity to enlarge total RAM and probably this query requires too much RAM to execute. Should Postgres just use HDD as temporary storage in this case?

Konstantin

> On 9 Jul 2019, at 12:53, Jean Louis <bugs(at)gnu(dot)support> wrote:
>
> * Konstantin Malanchev <hombit(at)gmail(dot)com <mailto:hombit(at)gmail(dot)com>> [2019-07-09 11:51]:
>> Hello,
>>
>> I'm running PostgreSQL 11.4 on Linux 4.12.14 and I see the following issue while executing single one query:
>> ERROR: could not resize shared
>> memory segment "/PostgreSQL.1596105766" to 536870912 bytes: No space left on device
>>
>> In my postgresql.conf I set sharred_buffers=256MB, I see that it is applied:
>> SHOW shared_buffers;
>> shared_buffers
>> ----------------
>> 256MB
>>
>> At the same time during the query execution, I see a lot of files in /dev/shm with the total size more than 256MB
>>
>> ls -lh /dev/shm
>>
>> How can I configure limit for total shared memory size?
>
> The limit is mostly set by the memory, as /dev/shm
> is like virtual memory or RAM disk.
>
> Increase the RAM.
>
> Jean