[firebird-support] Firebird's default settings
Hi! I have never tried to change Firebird's default settings, because the server has always been "good enough" and "if it isn't broken, don't fix it". But I can't help but wonder about some of the settings, because I don't understand their default values. Specifically, assuming Firebird 2.5 in the default install (which, I believe, is using SuperServer): - CpuAffinityMask - I can see why the value 1 would be a safe lower bound, but why doesn't the server default to a value which would use all available CPU cores? (That is, if CpuAffinityMask is not explicitly set, use all available CPUs.) Can I expect some adverse effects from setting CpuAffinityMask to 3 on a dual core system? - DefaultDbCachePages - why the value 2048? Given the usual settings, that means only 8 MB is used for database cache (per database). Today's computers tend to have 2 or more GB RAM, wouldn't it make more sense to default to 65536 or even 262144 pages? Again, if I increase the number to say 131072 pages (8192 bytes page size, one database only) on a 2.5 GB RAM system, can I expect any adverse effects? Thanks, Pepak ++ Visit http://www.firebirdsql.org and click the Resources item on the main (top) menu. Try Knowledgebase and FAQ links ! Also search the knowledgebases at http://www.ibphoenix.com ++ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/firebird-support/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/firebird-support/join (Yahoo! ID required) <*> To change settings via email: firebird-support-dig...@yahoogroups.com firebird-support-fullfeatu...@yahoogroups.com <*> To unsubscribe from this group, send an email to: firebird-support-unsubscr...@yahoogroups.com <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [firebird-support] Firebird's default settings
On Mon, Jul 16, 2012 at 4:46 AM, Josef Kokeš wrote: > Hi! > > Specifically, assuming Firebird > 2.5 in the default install (which, I believe, is using SuperServer): > > - CpuAffinityMask - I can see why the value 1 would be a safe lower > bound, but why doesn't the server default to a value which would use all > available CPU cores? (That is, if CpuAffinityMask is not explicitly set, > use all available CPUs.) Can I expect some adverse effects from setting > CpuAffinityMask to 3 on a dual core system? > The problem is that SuperServer is multi-threaded but not interlocked, so only one thread runs at a time so it cannot take advantage of multiple cores. Some operating systems move the process from one core to another in an attempt to balance load. That degrades performance, but can be prevented by setting the CPU affinity to a specific core. > > - DefaultDbCachePages - why the value 2048? Given the usual settings, > that means only 8 MB is used for database cache (per database). Firebird was designed to run with fewer than 100 pages in cache - the original version was validated with a ten page cache. Yes, no modern hardware, increasing the cache makes sense. > Again, if I increase the number > to say 131072 pages (8192 bytes page size, one database only) on a 2.5 > GB RAM system, can I expect any adverse effects? > Assuming you're using a 64 bit architecture for server and operating system, it should help. However, the usefulness of a large cache is somewhat application and data dependent, so I'd try it on a test machine rather than launching it directly in production. Good luck, Ann [Non-text portions of this message have been removed]
Re: [firebird-support] Firebird's default settings
> The problem is that SuperServer is multi-threaded but not > interlocked, so only one thread runs at a time so it cannot take > advantage of multiple cores. Some operating systems move the process > from one core to another in an attempt to balance load. That degrades > performance, but can be prevented by setting the CPU affinity to a > specific core. Ah. I see I misunderstood the release notes completely, then: The superserver is multithreaded, but it only applies to separate databases, so I would need to use 2 (4) databases AND set CPU affinity to get the benefit. Correct? Further reading seems to indicate that Firebird can't use multiple CPU cores for a single database in any threading mode, except for miscellaneous tasks such as sweep. Is this also correct? >> Again, if I increase the number to say 131072 pages (8192 bytes >> page size, one database only) on a 2.5 GB RAM system, can I expect >> any adverse effects? > > Assuming you're using a 64 bit architecture for server and operating > system, it should help. However, the usefulness of a large cache is > somewhat application and data dependent, so I'd try it on a test > machine rather than launching it directly in production. Could you please elaborate on the "assuming you're using a 64 bit architecture" part? If I calculate correctly, 128K cache pages with 8K page size should amount to 1G memory, which is safely withing reach of a 32bit application. Why would I need to use a 64bit system in this scenario? Note: I am assuming a dedicated server with only one database. Another question: I can see why a large cache fail to help performance in some cases, but, assuming there is enough memory for the cache, can it actually harm performance? Thanks for your answers. Pepak
Re: [firebird-support] Firebird's default settings
>> The problem is that SuperServer is multi-threaded but not >> interlocked, so only one thread runs at a time so it cannot take >> advantage of multiple cores. Some operating systems move the process >> from one core to another in an attempt to balance load. That degrades >> performance, but can be prevented by setting the CPU affinity to a >> specific core. > > Ah. I see I misunderstood the release notes completely, then: The > superserver is multithreaded, but it only applies to separate databases, > so I would need to use 2 (4) databases AND set CPU affinity to get the > benefit. Correct? Correct. This information is a bit hidden but there in the following Firebird 2.5 architecture comparison sheet: http://www.firebirdsql.org/file/fb25_architecture_comparison.pdf > Further reading seems to indicate that Firebird can't use multiple CPU > cores for a single database in any threading mode, except for > miscellaneous tasks such as sweep. Is this also correct? No. SuperClassic and Classic can take advantage of multiple cores for a single database. The following screencast might be helpful: http://www.iblogmanager.com/download/demos/firebird/fb25_architectures_smp.html -- With regards, Thomas Steinmaurer http://www.upscene.com/ >>> Again, if I increase the number to say 131072 pages (8192 bytes >>> page size, one database only) on a 2.5 GB RAM system, can I expect >>> any adverse effects? >> >> Assuming you're using a 64 bit architecture for server and operating >> system, it should help. However, the usefulness of a large cache is >> somewhat application and data dependent, so I'd try it on a test >> machine rather than launching it directly in production. > > Could you please elaborate on the "assuming you're using a 64 bit > architecture" part? If I calculate correctly, 128K cache pages with 8K > page size should amount to 1G memory, which is safely withing reach of a > 32bit application. Why would I need to use a 64bit system in this > scenario? Note: I am assuming a dedicated server with only one database. > > Another question: I can see why a large cache fail to help performance > in some cases, but, assuming there is enough memory for the cache, can > it actually harm performance? > > Thanks for your answers. > > Pepak > > > > > ++ > > Visit http://www.firebirdsql.org and click the Resources item > on the main (top) menu. Try Knowledgebase and FAQ links ! > > Also search the knowledgebases at http://www.ibphoenix.com > > ++ > Yahoo! Groups Links > > >
