Question re PHYSICAL_MEMORY_BYTES

From: William Wagman <wjwagman_at_ucdavis.edu>
Date: Tue, 24 Mar 2009 11:29:01 -0700
Message-ID: <2A8185DC02A8CE4C8413E0A26A8A831A0325A2F786_at_XEDAMAIL2.ex.ad3.ucdavis.edu>

Greetings,

I have been looking at AWR Reports on a two-node RAC cluster running RHEL4, 32-bit and Oracle 10.2.0.3 SE and comparing the PHYSICAL_MEMORY_BYTES value with the same information on another identical cluster and finding a big discrepancy in the values which I don't understand. I've been looking around and so far have not been able to come up with an explanation for what I am seeing. Let's take one cluster at a time. Both machines in the cluster have 4GB physical memory -

myucd1:/local/d02/oracle->cat /proc/meminfo

MemTotal:      4090376 kB
MemFree:        530076 kB
Buffers:        205836 kB
Cached:        2389484 kB
SwapCached:          0 kB
Active:        2832112 kB
Inactive:       386320 kB
HighTotal:     3211100 kB
HighFree:        64000 kB
LowTotal:       879276 kB
LowFree:        466076 kB
SwapTotal:     2096376 kB
SwapFree:      2096376 kB
Dirty:             332 kB
Writeback:           0 kB
Mapped:        1820464 kB
Slab:            94728 kB

CommitLimit: 4141564 kB
Committed_AS: 5474452 kB
PageTables: 225628 kB
VmallocTotal: 106488 kB
VmallocUsed: 7388 kB
VmallocChunk: 98664 kB

HugePages_Total:     0
HugePages_Free:      0
Hugepagesize:     2048 kB

Yet selecting from v$osstat shows only 916644 bytes -

SQL> select * from v$osstat;

STAT_NAME                             VALUE  OSSTAT_ID
-------------------------------- ---------- ----------
NUM_CPUS                                  4          0
IDLE_TIME                         591089966          1
BUSY_TIME                          30269232          2
USER_TIME                          12758301          3
SYS_TIME                           17435075          4
IOWAIT_TIME                        12346622          5
NICE_TIME                               301          6
RSRC_MGR_CPU_WAIT_TIME                    0         14
LOAD                             .709960938         15
NUM_CPU_SOCKETS                           2         17
PHYSICAL_MEMORY_BYTES                916644       1008

As I understand it PHYSICAL_MEMORY_BYTES should indicate the actual physical memory available so I don't understand why the discrepancy. I have not gathered system statistics and don't know if that would have an impact. It also doesn't make sense to me that being a node in a cluster would affect this but I don't know. Any help gratefully appreciated.

Thanks.

Bill Wagman
Univ. of California at Davis
IET Campus Data Center
wjwagman_at_ucdavis.edu
(530) 754-6208

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Received on Tue Mar 24 2009 - 13:29:01 CDT