We are using:

Windows 2000 SP4
Firebird-1.5.3.4870-0 SS
Apache2 2.0.52
PHP 5.1.2 (CGI-mode, with php_interbase.dll extension)
gds32.dll in Windows/system32 generated by FB1.5.3 instclient.exe i g
Database resides in c:\work\data and is aliased to alias1 in aliases.conf

C:\WINDOWS\system32\drivers\etc\services has the line:
gds_db 3050/tcp

All of this is running on one machine,
Everything is running ok while the load is lite.
I can connect to the FB server just fine through isql or through php.
But under heavy load (~90%+ cpu / 200+ concurrent database
connections) we get the following behaviors:

PHP:

ibase_connect("localhost:alias1", "SYSDBA", "masterkey");
returns:
Unable to complete network request to host "localhost". Failed to
establish a connection. No connection could be made because the target
machine actively refused it.

This happens periodically usually in batches (we have ~ 200 simultaneos
connections happening this way under load)

Firebird.log:
INTEL1-96502E87 (Client) Wed Feb 22 16:10:36 2006
Guardian starting: C:\Firebird\bin\fbserver.exe


INTEL1-96502E87 (Client) Wed Feb 22 16:13:48 2006
C:\Firebird\bin\fbserver.exe: terminated abnormally (4294967295)


INTEL1-96502E87 (Client) Wed Feb 22 16:13:49 2006
Guardian starting: C:\Firebird\bin\fbserver.exe


INTEL1-96502E87 (Client) Wed Feb 22 16:18:01 2006
C:\Firebird\bin\fbserver.exe: terminated abnormally (4294967295)


INTEL1-96502E87 (Client) Wed Feb 22 16:18:02 2006
Guardian starting: C:\Firebird\bin\fbserver.exe


INTEL1-96502E87 (Client) Wed Feb 22 16:25:38 2006
C:\Firebird\bin\fbserver.exe: terminated abnormally (4294967295)


INTEL1-96502E87 (Client) Wed Feb 22 16:25:39 2006
Guardian starting: C:\Firebird\bin\fbserver.exe

These logs seem to be unrelated to the PHP connection problems,
they are not happening at exactly the same time.

Any help would be greatly appreciated.

Thank you,

Dipesh