Adding memory, now slower?

[Gerry Tully]

My users tell me that after I added 8gb of ram to my N class system (total 14gb)it runs slower than before. Could this be possible? Os 11.0 9gb swap Oracle production server. Any ideas? Thanks

[Ken Hubnik_2]

Did the Oracle DBA's increase the size of the SGA for Oracle??

[Nag Varma]

Quickly you may want to check how the memory is arranged in the carriers...you can check this map with
" xstm "
Select memory right click for " information "
It shows how the memory is arranged..
this will give us a fair idea..whats wrong...

Next think swap as a thumb of rule is 1 1/2 times the physical memory...so you may want to ponder on this too..

thanks
Nag Varma

[harry d brown jr]

What is your dbc_max_pct and dbc_min_pct set to??

64bit??

live free or die
harry

[John Palmer]

What are you using the extra memory for? Have you increased the size of the Oracle SGA's?

It could be that if you haven't amended the kernel's buffer cache parameters then you may have a huge buffer cache.

Check dbc_max_pct, as it's a percentage of total memory it could be much too large.

Also I'd run glance to try to find where the bottlenecks are.

Regards,
John

[Gerry Tully]

Here are my replies:
No the DBA did not increase the sizes if the SGA
Attached is a copy of the mem info from xstm.
The db min/max are set to 5/15.

[A. Clay Stephenson · Accepted solution]

Surprisingly, under 11.0 when the size of the buffer cache exceeds about 800MB-1GB in many cases the performance actually decreases because of the overhead of so large a cache. For this reason, I tend to favor a fixed buffer cache by setting bufpages to a non-zero value. I suspect that you have dynamic buffer cache and your upper value is no so large that you are exceeding 800MB-1GB.

[Gerry Tully]

Clay, what would be a good value to set bufpages. I currently have it set to 0.

[John Palmer]

I think with this much memory, I'd fix the buffer cache at about 700Mb by setting both dbc_min_pct and dbc_max_pct to 5.

I'd also be looking to increase the Oracle SGA's unless you bought the memory in order to run additional workloads.

Regards,
John

[Sandip Ghosh]

Also if you are running 32bit oracle and multiple instances of oracle, I would look into the implementing of memory windows.

Sandip

[Gerry Tully]

Yes, we got the memory to run another application. Can't increase the SGA as we are up against the shared memory limitations and can't put memory windows on yet. Don't ask.
so, you recomment max/min db both set to 5 and bufpages set to 700mb?

[A. Clay Stephenson]

If you set the dbc_max_pct and dbc_min_pct, you are right back in the same boat when the amount of installed memory changes. I would set bufpages to no more than 204800 (800 MB) and you may well see better performance at 400MB (102400). Bufpages is the number of 4096 byte pages to allocate. By the way, leave nbuf at the default 0.

[Sandip Ghosh]

If oyu set the dbc_max_pct/min_pct to 5pct~700 MB you do not need to change the bufpages. You need to change it when it exceeds these values.

Sandip

[A. Clay Stephenson]

One other point: You mentioned that you have 9GB of swap with 14GB of memory; this is fine as long as swapmem=1 is set (pseudoswap enabled) otherwise anything above 9GB will not be used for process space.

[Nag Varma]

So Gerry,
what was the problem..curious to know..
thanks
Nag Varma

[Gerry Tully]

Nag,

I can't get the system yet to make the changes because of month end close. After they are done, I will be able to make the parameter changes. Probably in a week or so.