From: | Daniel Westermann <daniel(dot)westermann(at)dbi-services(dot)com> |
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To: | pgsql-general(at)postgresql(dot)org |
Subject: | Question on memory management sysv/posix on Linux |
Date: | 2016-02-17 10:26:33 |
Message-ID: | 1137430158.10758.1455704793888.JavaMail.zimbra@dbi-services.com |
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Lists: | pgsql-general |
Hi
I have a question about memory management in PostgreSQL. I understand the default on Linux usually is "posix" which creates files in /dev/shm. With the default settings of 128MB for shared_buffers this is the result:
ls -la /dev/shm
total 4
drwxrwxrwt 2 root root 60 Feb 17 11:19 .
drwxr-xr-x 18 root root 3100 Feb 17 09:36 ..
-rw------- 1 postgres postgres 2316 Feb 17 11:19 PostgreSQL.1804289383
Question: Why is this file only 2316 bytes?
Switching to sysv (same setting for shared_buffers):
ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0052e2c1 622592 postgres 600 56 5
0x6b8b4567 655361 postgres 600 2316 5
Again 2316 bytes. Why?
Is the 56 bytes segment related to Robert's post and only used for determining which processes are attached?
http://rhaas.blogspot.com/2012/06/absurd-shared-memory-limits.html
Thanks in advance
Daniel
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