Firebird 2.1 Release Notes

Global Improvements in Firebird 2.1
Bypass Filesystem Caching on Superserver
V. Khorsun
Feature requests CORE-1381 and CORE-1480
Firebird uses and maintains its own cache in memory for page buffers. The operating system, in turn, may recache
Firebird's cache in its own filesystem cache. If Firebird is configured to use a cache that is large relative
to the available RAM and Forced Writes is on, this cache duplication drains resources for little or no benefit.
Often, when the operating system tries to cache a big file, it moves the Firebird page cache to the swap, causing
intensive, unnecessary paging. In practice, if the Firebird page cache size for Superserver is set to more than 80
per cent of the available RAM, resource problems will be extreme.
Note
Filesystem caching is of some benefit on file writes, but only if Forced Writes is OFF, which is not recommended
for most conditions.
Now, Superserver on both Windows and POSIX can be configured by a new configuration parameter, Max-
FileSystemCache, to prevent or enable filesystem caching. It may provide the benefit of freeing more memory
for other operations such as sorting and, where there are multiple databases, reduce the demands made on host
resources.
Note
For Classic, there is no escaping filesystem caching.
For details of the MaxFileSystemCache parameter, see MaxFileSystemCache.
Garbage Collector Rationalisation
V. Khorsun
Feature request CORE-1071
Other Global Improvements
The background garbage collector process was reading all back versions of records on a page, including those
created by active transactions. Since back versions of active records cannot be considered for garbage collection,
it was wasteful to read them.
Immediate Release of External Files
V. Khorsun
Feature request CORE- 961
The engine will now release external table files as soon as they are no longer in use by user requests.
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