Re: OT - Blog entry on hugepages
Date: Wed, 4 Apr 2012 13:08:23 -0700
than paging and scanning stats that might be solved with largepages? Recently an AIX customer was seeing slow I/Os from an NFS filer but fast local I/O response times. Of course the customer blamed the NFS filer, but the filer reported constant speeds during good periods as well as bad. I suspected the network, but they were on 10GbE which looked to perform well. The customer claimed that on the database host box there was free CPU and that there was no scanning or paging out during the periods of NFS I/O slowdown. I personally didn't see the scanning or paging data. They were using some AIX tools that I wasn't familiar with and I didn't see vmstat output. Once the went to large pages the NFS read I/O slowdown went away, and they are convinced that it's the large pages that "fixed" the problem. Seems like it did, but I'm uncomfortable with the analysis. The only indication of memory pressure problems the customer gave was high SYS cpu which seems like a less than satisfactory way to identify a problem of memory pressure.
If I remember correctly, at "Brushco" (maybe some of the original players can chime in here) the first time I ran into largepage issues was on a Sequent almost 20 years ago where each process had a copy of the addressable process memory page table, so the larger the SGA, the more room these pagetables took up and the more databases process there were, the more memory was consumed by these process memory tables .By going to large pages the pagetable was smaller and less memory was used. This could be seen with memory issues that showed up in scanning and page outs.
On Thu, Mar 15, 2012 at 9:41 AM, Allen, Brandon <Brandon.Allen_at_oneneck.com>wrote:
> Just a small correction - the 64k pages in AIX are called "medium pages".
> The "large pages" in AIX are 16M and they require some extra
> configuration. For more detail:
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
> On Behalf Of Rich Jesse
> AIX, where the 64k largepages are self-managed in both AIX and Oracle.
> Privileged/Confidential Information may be contained in this message or
> attachments hereto. Please advise immediately if you or your employer do
> not consent to Internet email for messages of this kind. Opinions,
> conclusions and other information in this message that do not relate to the
> official business of this company shall be understood as neither given nor
> endorsed by it.