Connection number

Question

Inquiry about the Connection item in First connection attribute.
1. Connection exceed than setting connection attribute value.
The attribute values is set as Connection=10. But, more than 1000 connections are able to connect (all same in Process, thread and ttisql).
By looking at the document, tt_ref.pdf, setting the number of maximum connection is indicated. If the system still operates even though it reach the maximum setting connection value, what is this maximum values for?
2. If the connection exceed than setting value, does it cause any problem? Or, any effect on the resources(cpu, memory etc…) ?
3. If connection attribute does not really limits the connection number, is there any other way to control connection number?
4. When connection attribute’s values is set as 234, connection is unable and gives a error code(925).
It’s occurred on Linux system and setting values of semaphore is 'kernel.sem = 250 32000 100 128'.
What brings this error?

Answer 1

There is often confusion around this parameter. It is really a performance optimisation parameter. It does not limit the number of connections but affects the mechanism by which connections wait for locks if they cannot acquire them immediately. The first 'n' connections (in Connections=n, default is 64) use an efficient semaphore based lock wait mechanism while connections beyond this number use a less efficient mechanism.
We would normally recommend that you set this value to a few more than the maximum humber of concurrent connections that you expect there to be. Note that if you do increase this beyond the default you may also need to increase the number of semaphores defined in the kernel as (each connection requires a semphore) otherwise you will get the error that you are seeing :-)
Regards,
Chris