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 re-cache 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, MaxFileSystemCache, 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.

Other Global Improvements

Garbage Collector Rationalisation

V. Khorsun

Feature request CORE-1071

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 CORE961

The engine will now release external table files as soon as they are no longer in use by user requests.

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Global Improvements in Firebird 2.1

Synchronization of DSQL metadata cache objects in Classic server

A. dos Santos Fernandes

Feature request CORE-976

No details.

BLOB Improvements

A. dos Santos Fernandes

Feature request CORE-1169

Conversion of temporary blobs to the destination blob type now occurs when materializing.

Type Flag for Stored Procedures

D. Yemanov

Feature request CORE-779

Introduced a type flag for stored procedures, adding column RDB$PROCEDURE_TYPE to the table RDB $PROCEDURES. Possible values are:

- 0 or NULL -

legacy procedure (no validation checks are performed)

- 1 -

selectable procedure (one that contains a SUSPEND statement)

- 2 -

executable procedure (no SUSPEND statement, cannot be selected from)

Help for Getting Core Dumps on Linux

A. Peshkov

Feature request CORE-1558

The configuration parameter BugcheckAbort provides the capability to make the server stop trying to continue operation after a bugcheck and instead, to call abort() immediately and dump a core file. Since a bugcheck usually occurs as a result of a problem the server does not recognise, continuing operation with an unresolved problem is not usually possible anyway, and the core dump can provide useful debug information.

In the more recent Linux distributions the default setups no longer dump core automatically when an application crashes. Users often have troubles trying to get them working. Differing rules for Classic and Superserver, combined with a lack of consistency between the OS setup tools from distro to distro, make it difficult to help out with any useful “general rule”.

Code has been added for Classic and Superserver on Linux to bypass these problems and automate generation of a core dump file when an abort() on BUGCHECK occurs. The Firebird server will make the required 'cwd' (change

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Global Improvements in Firebird 2.1

working directory) to an appropriate writable location (/tmp) and set the core file size limit so that the 'soft' limit equals the 'hard' limit.

Note

In a release version, the automated core-dumping is active only when the BugcheckAbort parameter in firebird.conf is set to true (1). In a debug version, it is always active.

If you need to enable the facility, don't forget that the server needs to be restarted to activate a parameter change.

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