How much physical memory is Oracle using?

[Haitham Hamad]

I have two D350 servers each having 256MB of RAM and 1G of swap. Both are running 1 Oracle instance with SGA size of 245MB. Attached is the Glance output of Both servers. I have users connecting to the database through oracle forms available from the servers and others are using the servers as NFS servers to store local files. Attached is the output of Glance. The first server is a lot slower than the first one and cannot figure out why. I know that I need more memory but still both system have the same memory. The only logical explanation that I have is that out of the user memory available, the first server's SGA is not getting as much memory as the second server's SGA and it is competing with the NFS connections?. Please correct me if I am wrong. How do I find out how much "physical memory" the SGA is using and how much the NFS connections are using?. Is the buffer cache having any affect since it is higher on the second server but both have dbc_max_pct of 50.

TIA, Haitham

[Haitham Hamad]

Here is the attachment

[Roger Baptiste]

hi,

firstly, for 256Mb of RAM,
the setting of dbc_max_pct
is way too high for 50.
Reduce it to 10 and dbc_min_pct to 5.

>
UNIX95= ps -e -o vsz=Kbytes -o ruser -o pid,args=Command-Line |grep oracle |sort -rnk1

Also, you can look at
ipcs -am |grep oracle.

With 256Mb , there is little
you can do nitpicking on memory usage. NFS shouldnt make that much of a difference on memory usage. It is probale that one of the system's database is more active.

I would suggest to change
the dbc values (reduce them).
Also, for such a small memory, it is pointless to
have pseudo swap . So, if you have pseudoswap , disable it.

The easiest way is to add additional memory.

-raj

[Alan Riggs]

The SGA will use exactly as much physical memory as the size you specify. If it cannot find a contiguous shared memory segment of the appropriate size, the database will not start. You can check the size with ipcs -ma.

Your buffer settings do not appear to be 50%, and you are, in fact, using more buffer space on the fast system. I doubt that decreasing buffer size will help. The 20MB being used on the slow system might even be too low. That really depends on what else is running on the servers, since oracle does its own buffering.

Question: do you have online JFS, and if so are you using oracle's recommended mount options? Without them, oracle data gets buffered twice, hurting performance.

You are doing more paging on the slow system. This might be a function of data use as much as configuration. Since you are paging, though, you should do everything possible to optimize the disk access speeds of your sawap areas.

Are the servers identical in their disk speeds, etc? Is the data layout identical (or close?). Have you taken care to segregate index from data space?

[harry d brown jr]

I wouldn't run oracle on any machine with less than 3/4 of a gb. Oracle is a pig and loves to consume resources. Your performance will be improved if you get more memory. I noticed you are paging also, and more memory will take care of that (well sometimes).

live free or die
harry

[Haitham Hamad]

My understanding is that UNIX will try to assign the shared memory for Oracle from the total virtual memory it has (not the physical memory). What happens when a buffer cache needs more memory that is not physically available, Does the SGA starts paging out?? ipcs -ma shows me the amount of shared memory but not the physical amount of memory used by oracle at a specific moment. Does the sz column in ps -efl shows that value. RajMan, I couldnot use the -o option.

[Uday_S_Ankolekar]

Hi,
This could help you
UNIX95= ps -e -o vsz=Kbytes -o ruser -o pid,args=Command-Line | sort -rnk1 | more

-USA..

[Jim Turner]

How much physical memory is Oracle using? The easy answer is too damn much, but that's why Oracle is fondly known as a virus. Seriously, though . . .

If anything loads before Oracle which would push part of Oracle's SGA into swap, you're pooched. Check the memory report in Glance on both your machines. I think you will find the slower machine to have consistent VM Reads and Writes where the faster machine doesn't.

And to echo what has already been said, 256MB of RAM is absurdly low for Oracle. You need more physical RAM. Lots more. What you are currently trying to do is akin to pulling a freight train with a motorcycle.

Cheers,
Jim

[harry d brown jr]

Haitham ,

Don't worry about the buffer cache, it'll take care of itself. If you have buffer cache too large, then apps, like oracle have less memory to play with. r% min and 10% max are good numbers to use, but rarely ever 50%.


live free or die
harry

[harry d brown jr]

That was supposed to be 5% min and 10% max (I think I fat fingered that one!).

live free or die
harry