Re: Solaris Priority Paging and Database products.

Hi All!

My standpoint on prioroty paging is, why not implement it, because, *it can only help*.
It's a tweak to the way Solaris manages it's buffercache, and it's a tweak for the better.

The white paper
at http://www.sun.com/sun-on-net/performance/priority_paging.html claims "performance gains between 10-300% on customer workloads". Well I certainly haven't seen that kind of dramatic improvement since implementing it a few months ago, but I guess it all depends on your workload, type of apps used, etc.

I do agree with the previous post in this thread that page-stealing (which is the activity that priority paging seeks to tweak) only occurs when you're running low on memory, so it follows that prioroty paging will only "come to the fore" in instances of memory contention. So it's not a general panacea, but rather IMHO a "good ace to have up your sleave" if and when you start to run into memory shortages.

Another important thing to note is that you must take pains to ensure that data files do not have their executable bits set, because this will fool the VM manager into thinking it's an executable, thereby subverting the priority algorithm. Hope you don't have f/s's with millions of data files default umask'd to 0755, or you're in for a pretty lengthy find -perm ...

I believe you can set p.p. dynamically on a running system via some ndd incantation. If so I guess you could do some performance tests... just make sure you pass on the results to the n.g. :)

Your post metions p.p. with specific reference to db products. As well as SA'ing Solaris I DBA a smallish (4GB) Informix installation. I did not notice any great leaps in performance of the RDBMS with the implementation of p.p., but I'd have to say that any effects were more than likely masked by the 100 other performance tweaks I'm continually implementing. To diverge from the topic just a little, if your talking databases and memory, your best friend is the the forcedirectio (man mount_ufs(1M)) mount option. This only applies if you're using cooked ufs files for your db files (most Oracle sites), rather than raw devices (most Informix sites), but if you are using cooked files, forcedirectio will save your db from swamping from vm buffercache with data that's already in it' own cache anyway. But I digress :)

Cheers
Andrew

Std.disclaimer: forget you read this, it's all crap, blah blah blah...

Richard Yates wrote:
>
> A quick question - has anyone implemented priority paging on Solaris
> and noticed a performance change with their database product? If so,
> I shall be very interested to hear any conclusions reached! I have
> done some testing, but due to certain factors formed no firm ideas,
> other than "it *should* be a good thing".
>
> Richard Yates.

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Share what you know. Learn what you don't. Received on Sat Sep 11 1999 - 00:00:00 CEST