topic Re: memory performance question 11.0 64 bit in Operating System - HP-UX

memory performance question 11.0 64 bit

Penni Nussbaum — Thu, 26 Apr 2001 18:40:11 GMT

I have an 11.0 system (64 bit) with memory (according to Glance) as follows..
phys mem 2 gb
user mem 1.36 gb
free mem 332.4 mb
sys mem 115.8
buf cache 204.8
total vm 765.5
active vm 723.3

This is an oracle database server. It keeps on getting memory shortage problems. There is 1 gig of swap. I don't have any more disks to add more swap. Pseudo swap is turned on.

bufpages = 0
db max =10
db min = 2
nbuf =0

Besides adding more memory, does anyone have tuning ideas? Also, the developer is sure that Oracle is using only 1 gig of memory. He wants to know why the OS requires 1 gig (He assumes this since we are getting memory errors when no one can telnet into the box).

Re: memory performance question 11.0 64 bit

Thierry Poels_1 — Thu, 26 Apr 2001 18:46:29 GMT

hi,
If the server is mainly an Oracle database server then you should minimize the file cache:
set dbc_min & dbc_max = 2
just my 2 cents,
Thierry.

Re: memory performance question 11.0 64 bit

A. Clay Stephenson — Thu, 26 Apr 2001 18:49:14 GMT

First thing let's see how much shared memory Oracle is eating. ipcs -m -a. Also get some page/in and especially page/out rates via glance.

Re: memory performance question 11.0 64 bit

Penni Nussbaum — Thu, 26 Apr 2001 18:52:47 GMT

Re: memory performance question 11.0 64 bit

A. Clay Stephenson — Thu, 26 Apr 2001 19:08:25 GMT

Next question, you appear to have 3 oracle instances running. Is this correct?

Re: memory performance question 11.0 64 bit

Penni Nussbaum — Thu, 26 Apr 2001 19:10:49 GMT

yep, 3 instances.

Re: memory performance question 11.0 64 bit

A. Clay Stephenson — Thu, 26 Apr 2001 19:25:59 GMT

Are you using raw disk for database I/O (or vxfs mount options mincache=direct, convosync=direct (both bypass the UNIX buffers)?
If so really reduce the buffer cache sizes so that Oracle is not buffering in both the SGA's and the Unix Block I/O Buffers. Thierry's suggestion is a good one. I would prefer to set bufpages to about 15360 (60MB) if this is a pure database server.

I would also ask the DBA to reduce his buffers
a bit (especially on any of the non-production instances) to see if this helps.

If you are using cooked files for datafiles/indexes and you have OnLineJFS I strongly suggest that you use the mount options mentioned above to avoid the double buffering. No database changes will be required.

Hopr some of this helps...

Re: memory performance question 11.0 64 bit

A. Clay Stephenson — Thu, 26 Apr 2001 19:32:17 GMT

One other thing Penni:
Are the glance snapshots you're sending taken when thinks are pretty good or when the box is a dog? Things don't look so terrible so far.
When things are bad it would also be nice to have some idea of run queue sizes as well.

Re: memory performance question 11.0 64 bit

Thierry Poels_1 — Fri, 27 Apr 2001 05:59:28 GMT

Hi,
I agree with Clay; the system statistisch you showed us, don't look like an overloaded system.
And (also mentioned by Clay, I'm just repeating ;) check if you can shrink some SGA-sizes. They seem to consume a considerable amount of memory; but size depends on your setup, size of database, users, etc. so I'm not going to state that they really are to big.

One more thing I noticed is the amount of swapspace used: 95%. You might need to increase your swapspace.
Thierry.

Re: memory performance question 11.0 64 bit

Carlos Fernandez Riera — Fri, 27 Apr 2001 10:31:52 GMT

The amount of recomended swap is two times phisical memory and you have configured a half.

To add swap you need disk space but in 11.0 swap could be in any vg.

By the other hand, you there are running 3 oracle instances with shared memory sizes (SEGMENT SIZE) of about 200, 254 and 500 Mb each, this is 1 Gb, plus 10% of buffer cache get 1,2 Gb of memory used with out users.

If realy you can not increase swap ( that is what you need), try to reduce shared memory usage.

Run swapinfo... you are near to the message "not enough memory" ....

Re: memory performance question 11.0 64 bit

Penni Nussbaum — Fri, 27 Apr 2001 10:54:43 GMT

The statistics I showed are not when the system was low on memory. When the system is low on memory, no one can log on.

I realize I need to increase sap size, but there is no more disk space anywhere on this system. No free disks and the no gree space on any volume groups.

One of thehigh level users is questioning why the system needs almost 1 gig of memory (Oracle needing the other). I need to defend that 1 gig.

Re: memory performance question 11.0 64 bit

Penni Nussbaum — Fri, 27 Apr 2001 11:01:52 GMT

Regarding mincache=direct and convosync, it is my understanding these options need Online JFS, which we do not have here.

Re: memory performance question 11.0 64 bit

Penni Nussbaum — Fri, 27 Apr 2001 11:24:48 GMT

One more question. Although I only have 1 gig of swap with 2 gig of memory, I do have the kernel parameter swapmem_on set to 1. I thought turning this on helps alleviate the swap shortage.

Re: memory performance question 11.0 64 bit

Carlos Fernandez Riera — Fri, 27 Apr 2001 11:37:35 GMT

Perhaps this help:

When you start a new process ( like telnet) the kernel reserve space in swap to use if is needed. If you have not enough swap the system cant reserve swap then and then message issued is not " more swap needed" the message is not enought memory.

This is not a problem of memory, the problem is swap.

If you can not add disk, then reduce memory usage. That oracle instance of 505 Mb of shared memory maybe could be reduced ( raising db_block_buffers, or shared_pool_size.

Choosing between performance and accessibility... i dont need performance if i cant access!.

Re: memory performance question 11.0 64 bit

Servio Cabrera — Fri, 27 Apr 2001 12:06:01 GMT

I have seen, when you apply the kernel template for Monolitic DB server, it put swapmen=0, and I heard some experts dont recomend swapmem=1, for a DB server. But if you do that, you have to increase the swapspace even more to compensate. If you are mirroring the swap lv, try to break the mirror and use the freed space for another swap lv, so you will double. And again, reduce the db_max_pct to 2%

Re: memory performance question 11.0 64 bit

Stefan Farrelly — Fri, 27 Apr 2001 12:17:02 GMT

Youve simply got to have swap size set to the same as memory, at a minimum. You really need 2 GB of swap. Using pseudo-swap is not an alternative as this will cause memory contention and performance degredation, especially as you only have 300 odd MB free which means your using 700MB of pseudo swap instead of swapspace. Pseudo-sawp is a backup (for emergencies when your really out of memory) not as an alternative to swapspace.

Increase swapspace to 2GB and you will be surprised how much better your system performs.

Re: memory performance question 11.0 64 bit

Penni Nussbaum — Fri, 27 Apr 2001 12:21:43 GMT

Thanks. I cannot change kernel parameter because of the reboot, but I did unmirror my swap which doubled the size. I'll see what happens today.

Re: memory performance question 11.0 64 bit

Carlos Fernandez Riera — Fri, 27 Apr 2001 19:47:07 GMT

Shit man...

If you need a kings reponse you should say it before...

There was 3 hated saying what was the problem.

Re: memory performance question 11.0 64 bit

Thierry Poels_1 — Sat, 28 Apr 2001 05:23:45 GMT

LOL Carlos. Yep Penni seems to be very selective in giving points ;)
Personally I would prefer some feedback on how things are going after the swap increase (you did really add swap space, not just decreased the mirror) than getting points without knowing what did the trick.
regards,
Thierry.

Re: memory performance question 11.0 64 bit

A. Clay Stephenson — Sat, 28 Apr 2001 21:35:35 GMT

Penni: You cheated when you told us that you had no more disks for swap and then ... oops I unmirrored swap. I took you at your word and was trying everything I could to avoid using filesystem swap which was the only option left.