I have a dual cpu box with 2GB RAM dedicated to running Postgres.
Last week, I upgraded FreeBSD from 4.4-STABLE to 4.6-RELEASE-p1. When
I went to restart postgres, it complained that it could not allocate
the shared memory segment. I'm running Postgres 7.2.1.
For those familiar with postgres, I was using shared_buffers=100000
with 4.4, but had to back that down to 32000 for 4.6. This is
obviously impacting performance...
The kern.ipc.* settings have not changed. In my /etc/sysctl.conf
file, I set
kern.ipc.shmmax=268435456
kern.ipc.shmall=65535
kern.ipc.shm_use_phys=1
With FreeBSD 4.6, I even upped the shmmax to 1073741824 to no avail.
I also set this in the kernel (so as to eliminate any issues with
setting it at boot time).
However, it does produce a most peculiar error message when running
postgres:
-- cut here --
IpcMemoryCreate: shmget(key=5432001, size=665346048, 03600) failed: Cannot allocate memory
This error usually means that PostgreSQL's request for a shared
memory segment exceeded available memory or swap space.
To reduce the request size (currently 665346048 bytes), reduce
PostgreSQL's shared_buffers parameter (currently 80000) and/or
its max_connections parameter (currently 48).
-- cut here --
Now, by my arithmetic, 665346048 is certainly less than 1073741824 by
quite a bit.
I did not recompile postgres after the FreeBSD upgrade.
Has something changed from 4.4-STABLE that would cause such a failure?
The funny thing is that it worked just fine with FBSD 4.4 and the
lower setting of shmmax (even with 100000 shared_buffers), so
something is making postgres try to allocate a larger hunk of memory.
I just don't know what.
Any advice would be appreciated.
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Vivek Khera, Ph.D. Khera Communications, Inc.
Internet: khera@kciLink.com Rockville, MD +1-240-453-8497
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