Memory Utilization in N4000

[Richard Zanni]

I may have an issue with memory capacity on an N4000, running Oracle on 11.0 with 4GB of RAM. I've read several other postings concerning the question of memory utilization. From what I gather, memory utilization can be important, but even more telling is the pageout rate.

I ran a "vmstat 5 5000" during working hours and also glance. There are several periods (on the order of less than a minute) throughout the day when we are paging out at ~60. Glance shows we do hit 100% also.

My question is this: I've read that pageout rates of 50~60 could indicate the need for more memory. I do see this from vmstat, but it seems sporadic and most of the day we are not pageing out at all (or very little).

I've included the output from the vmstat. Here's a screen shot of glance:

B3692A GlancePlus C.03.05.00 08:09:44 pwm-d-0 9000/800 Current Avg High
--------------------------------------------------------------------------------
CPU Util SU U | 9% 5% 76%
Disk Util FF | 3% 6% 100%
Mem Util S SU UB B | 96% 79% 100%
Swap Util U UR R | 36% 30% 42%
--------------------------------------------------------------------------------
MEMORY REPORT Users= 2
Event Current Cumulative Current Rate Cum Rate High Rate
--------------------------------------------------------------------------------
Page Faults 3 16179485 0.6 187.4 8599.0
Page In 2 6278060 0.4 72.7 3256.0
Page Out 0 36361 0.0 0.4 321.3
KB Paged In 0kb 757.3mb 0.0 8.9 932066.6
KB Paged Out 0kb 609.8mb 0.0 7.2 7248.4
Reactivations 0 24205 0.0 0.2 4.5
Deactivations 0 24205 0.0 0.2 3.3
KB Deactivated 0kb 228kb 0.0 0.0 12.3
VM Reads 0 46966 0.0 0.5 135.7
VM Writes 0 76084 0.0 0.8 666.5

Total VM : 2.63gb Sys Mem : 222.3mb User Mem: 3.29gb Phys Mem: 4.00gb
Active VM: 670.1mb Buf Cache: 327.7mb Free Mem: 182.0mb

(BTW, dbc_max_pct is set at 8%.)

Thanks for your help...

[Steve Steel]

Hi

Look at the page shown here.

Also good tools

Memory Usage (â What is using all of the memoryâ ?)

by:eric.herberholz@hp.com

Last modified: March 23, 2004

Latest version also available at external ftp site:

ftp://eh:spear9@hprc.external.hp.com/memory.htm


Steve

[Stefan Farrelly]

What does swapinfo -mt show ? The device USED lines show much memory has been swapped out - I reckon its in the hundreds of MB.

The whole point of a database server is to NEVER allow it to runout of ram as performance degrades by a huge factor if it does. Youve got too much user ram (almost 3.3GB out of 4GB total) being used. Either reduce the size of your database SGA or get some users off or if you cant add more ram.

[Richard Zanni]

root >swapinfo -mt
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 10512 174 10338 2% 0 - 1 /dev/vg00/lvol2
reserve - 4310 -4310
memory 3079 589 2490 19%
total 13591 5073 8518 37% - 0 -

What is a "SGA"? I'm not a db person.

[Stefan Farrelly]

Well, youre currently only 174MB swapped out which isnt too bad (although we keep this to ZERO on all our oracle servers). You need to keep an eye on the swapinfo command when you suffer a period of high paging - to see how much ram in total gets paged (the used line on device).

You can check how much shared memory your oracle database is hogging with this command;
ipcs -ma | grep oracle
The size in bytes is in the SEGSZ column. Your dba's can reduce it if its too big (in the Gb).

[Richard Zanni]

root >ipcs -ma | grep oracle
m 385030 0x267baad4 --rw-rw---- oracle oinstall oracle oinstall 308 980885504 4115 4104 9:03:09 9:03:5
9 12:30:09
m 22535 0xda9bc90c --rw-r----- oracle oinstall oracle oinstall 12 164859904 29683 14302 6:11:23 7:00:3
2 12:00:10
m 1126408 0x41534f52 --rw-rw-rw- oracle oinstall oracle oinstall 1 1800 8261 4110 8:59:38 no-entry 1
3:39:42

Thanks for your help Stefan!

[Jean-Luc Oudart]

Check the memory usage for your database(s).
Reduce the non-used areas (do you use java ? if not reduce java pool, ...)

you can also tune the shared memory.
cf. attached script (pool_estimate.sql)

finally reduce the SGA.

Also I would suggest you run statspack before and after the different changes to check the oracle processing improvements

Regards,
Jean-Luc