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CHAPTER 12 Managing System Resources
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The
JAVA_NAMESPACE_SIZE option of the SET OPTION command sets the
maximum size (in bytes) of that part of the memory that is allocated to Java
applications on a per database basis. Per database memory allocations include
Java class definitions. As class definitions are effectively read-only, they are
shared among connections. Consequently, their allocations come right out of
the fixed cache, and this option sets a limit on the size of these allocations.
The process threading model
Adaptive Server IQ uses operating system kernel threads to improve
performance. Threads can be found at the user level and at the kernel level.
Lightweight processes are underlying threads of control that are supported by
the kernel. The operating system decides which lightweight processes (LWPs)
should run on which processor and when. It has no knowledge about what the
user threads are or how many are active in each process.
The operating system kernel schedules LWPs onto CPU resources. It uses their
scheduling classes and priorities. Each LWP is independently dispatched by the
kernel, performs independent system calls, incurs independent page faults, and
runs in parallel on a multiprocessor system.
Adaptive Server IQ Version 12 uses a simpler process threading model than
previous versions. Instead of multiple processes for each CPU shuttling among
users, there is now a single, highly threaded process that serves all Adaptive
Server IQ users. Adaptive Server IQ assigns varying numbers of kernel threads
to each user connection, based on the type of processing being done by that
process, the total number of threads available, and the setting of various
options.
The following figure shows kernel threads for various users as they are
distributed across multiple CPUs.