Capitalizing On The Aix System Libraries; Using The Thread_Post_Many Api; File Systems - IBM Power7 Optimization And Tuning Manual

When you uninstall a DB2 copy in a global environment, all associated instances must be
dropped or updated to another DB2 copy and its corresponding system WPARs must
be active.
When you apply fix packs to a DB2 copy in a global environment, all associated instances
must be stopped and its corresponding system WPARs must be active.
For information about installing a DB2 copy on a WPAR, see Chapter 8, "Workload
Partitioning", in Best Practices for DB2 on AIX 6.1 for POWER Systems, SG24-7821.
For more information about this topic, see 8.8, "Related publications" on page 144.

8.5 Capitalizing on the AIX system libraries

This section describes methods for capitalizing on the AIX system libraries.

8.5.1 Using the thread_post_many API

DB2 uses thread_wait and thread_post_many to improve the efficiency of DB2 threads
running on multi-processor Power Systems. DB2 takes advantage of the thread_post_many
function. The availability of such an API on AIX directly impacts the efficiency of DB2
processing, as it allows for waking many EDUs with a single function call, which in other
operating systems requires many individual function calls (typically as many as the number of
EDUs being woken up).

8.5.2 File systems

DB2 uses most of the advanced features within the AIX file systems. These features include
Direct I/O (DIO), Concurrent I/O (CIO), Asynchronous I/O, and I/O Completion Ports (IOCP).
Non-buffered I/O
By default, DB2 uses CIO or DIO for newly created table space containers because
non-buffered I/O provides more efficient underlying storage access over buffered I/O on most
workloads, with most of the benefit that is realized by bypassing the file system cache.
Non-buffered I/O is configured through the NO FILE SYSTEM CACHING clause of the table space
definition. To maximize the benefits of non-buffered I/O, a correct buffer pool size is essential.
This size can be achieved by using STMM to tune the buffer pool sizes. (The default buffer
pool is always tuned by STMM, but user created buffer pools must specify the automatic
keyword for the size to allow STMM to tune them.) When STMM is enabled, it automatically
adjusts the buffer pool size for optimal performance.
For file systems that support CIO, such as AIX JFS2, DB2 automatically uses this I/O method
because of its performance benefits over DIO.
The DB2 log file by default uses DIO, which brings similar performance benefits as avoiding
file system cache for table spaces.
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POWER7 and POWER7+ Optimization and Tuning Guide