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Limited Shared Buffer Problem

From: "**Rod MacNeil" <rmacneil(at)interactdirect(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Limited Shared Buffer Problem
Date: 2010-01-29 16:37:55
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hi All,

I have a server running CentOS5 with 6gb of memory that will run postgres
8.3 exclusively.
I would like to allocate 4gb of the memory to shared buffers for postgres.
I have modified some kernel settings as follows:

shmall  1048576 pages  4,294,967,296 bytes
shmmax 4,294,967,295 bytes

I can set the postgres config to shared_buffers = 2700MB but no higher.
If I try shared_buffers = 2750MB the server fails to start with a message it
cannot allocate memory:

2010-01-29 11:24:39 EST FATAL:  shmat(id=1638400) failed: Cannot allocate

Is there some other setting that could be limiting the amount I can

Excerpt from postgresql.conf:

# - Memory -

shared_buffers = 2750MB                 # min 128kB or max_connections*16kB
                                        # (change requires restart)
temp_buffers = 32MB                     # min 800kB
max_prepared_transactions = 10          # can be 0 or more
                                        # (change requires restart)
# Note:  Increasing max_prepared_transactions costs ~600 bytes of shared
# per transaction slot, plus lock space (see max_locks_per_transaction).
work_mem = 2MB                          # min 64kB
maintenance_work_mem = 32MB             # min 1MB
#max_stack_depth = 2MB                  # min 100kB

Any help appreciated, Thanks



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Subject: Re: Limited Shared Buffer Problem
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Subject: Constraint propagating for equal fields

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