>>> So, what I'm saying is that MaxFileSystemCache may be useful for classic
>>> as well, in some situations. I haven't tried it though. Still on 2.1.
>>
>> And you speak about FileSystemCacheSize setting which was introduced
>> in v2.5 and allows to limit size of file system cache. This is system-wide
>> setting and it is fully independent of Firebird's usage of file system cache.
>
> I'm confused now. ;-) I don't find FileSystemCacheSize in firebird.conf,
> thus I guess it isn't a V2.5 setting?
It was introduced in v2.5 :) Probably you have copied firebird.conf from
older version
when installed your v2.5.
> So, in respect to memory usage: Is the worst case that pages are cached
> in both, Firebird page cache and OS file system cache? Is this possible?
If Firebird is using file system cache (and by default it used) then double
caching
(by both FB and OS) is in place. If RAM is not enough for both caches (set of
active
pages in DB can't fit into each of the caches) there will be competition for
memory
and sooner of all OS will intensively use its own page file (AKA swap file)
creating
additional IO load.
Therefore, if you plan to make huge page cache in Firebird it have sence to
try to
disable file system caching. By default, file system cache will be disabled for
particular
database if Firebird's cache for that database is more than 65536 pages.
Note, Firebird have no such features as pre-fetch (or read-ahead) and
multy-block IO,
therefore it will be slower at physical IO than file system. Also, disabled
file system
cache means enabled Forced Writes, despite of database setting (at least on
Windows).
Regards,
Vlad
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