Hi Robert, Thank you! Holy mackerel! That's a lot of memory. With that type of a calculation my 4GB arc_max setting is still in the danger zone on a Thumper. I wonder if any of the ZFS developers could shed some light on the calculation?
That kind of memory loss makes ZFS almost unusable for a database system. I agree that a page cache similar to UFS would be much better. Linux works similarly to free pages, and it has been effective enough in the past. Though I'm equally unhappy about Linux's tendency to grab every bit of free RAM available for filesystem caching, and then cause massive memory thrashing as it frees it for applications. Best Regards, Jason On 1/10/07, Robert Milkowski <[EMAIL PROTECTED]> wrote:
Hello Jason, Wednesday, January 10, 2007, 9:45:05 PM, you wrote: JJWW> Sanjeev & Robert, JJWW> Thanks guys. We put that in place last night and it seems to be doing JJWW> a lot better job of consuming less RAM. We set it to 4GB and each of JJWW> our 2 MySQL instances on the box to a max of 4GB. So hopefully slush JJWW> of 4GB on the Thumper is enough. I would be interested in what the JJWW> other ZFS modules memory behaviors are. I'll take a perusal through JJWW> the archives. In general it seems to me that a max cap for ZFS whether JJWW> set through a series of individual tunables or a single root tunable JJWW> would be very helpful. Yes it would. Better yet would be if memory consumed by ZFS for caching (dnodes, vnodes, data, ...) would behave similar to page cache like with UFS so applications will be able to get back almost all memory used for ZFS caches if needed. I guess (and it's really a guess only based on some emails here) that in worst case scenario ZFS caches would consume about: arc_max + 3*arc_max + memory lost for fragmentation So I guess with arc_max set to 1GB you can lost even 5GB (or more) and currently only that first 1GB can be get back automatically. -- Best regards, Robert mailto:[EMAIL PROTECTED] http://milek.blogspot.com
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