IBM Power7 - Page 206

190 POWER7 and POWER7+ Optimization and Tuning Guide
– 64 KB page use for data, text, and stack is implemented separately from 64 KB pages
for the SGA, and is done through an environment variable that is exported on behalf of
the Oracle user:
$ export LDR_CNTRL=DATAPSIZE=64K@TEXTPSIZE=64K@STACKPSIZE=64K oracle
* LDR_CNTRL=DATAPSIZE=64K@TEXTPSIZE=64K@STACKPSIZE=64K
export LDR_CNTRL
CPU
CPU specifications are as follows:
򐂰 SMT mode: POWER7 supports SMT4 mode, which is the AIX default. AIX and Oracle
performance support encourages starting with the default.
򐂰 Virtual processor folding: This is a feature of Power Systems in which unused virtual
processors are taken offline until demand requires that they be activated. The default is to
allow virtual processor folding; do not alter this setting without consulting AIX support.
򐂰 Specific to POWER7 SMT4 mode: Certain Oracle 11G parameters, including
DB_WRITER_PROCESSES and PARALLEL_MAX_SERVERS, are partly derived from CPU_COUNT, and
CPU_COUNT is equal by default to the number of logical CPUs. CPU_COUNT automatically
adjusts to changes in virtual processor count and to SMT mode, up to three times the
value on startup.
򐂰 When you migrate from single-threaded platforms to Power Systems, or from POWER5 or
POWER6 to POWER7 with SMT4 mode, the value of CPU_COUNT also increases, affecting
DB_WRITER_PROCESSES, PARALLEL_MAX_SERVERS, and other dependent parameters. Queries
that are sensitive to a degree of parallelism might change behavior because of the
migration to POWER7. Reviewing the PARALLEL_MAX_SERVERS parameter after migration,
but set DB_WRITER PROCESSES to the defaults.
I/O
I/O specifications are as follows:
򐂰 If ASM is not used, use max interpolicy striping (also known as
pp spreading or poor man’s
striping
) when logical volumes are created. To get the most benefit from spreading
physical partitions across the LUNs, use a small physical partition size, for example,
32 MB or 64 MB.
򐂰 Async I/O is used even with Concurrent I/O (CIO):
– With AIXV 6.1 and AIX V7.1, start with the asynchronous I/O defaults. With AIX V6.1,
there is a new implementation of AIO. AIO kernel extensions are loaded at system boot
(always loaded), AIO servers stay active if there are service requests, and the number
of AIO servers is dynamically increased or reduced based on demand of the workload.
The aio_server_inactivity parameter defines how many seconds of idle time before
an AIO server exits. AIO tunables are now based on logical CPU count, and it is usually
not necessary to tune minservers, maxservers, and maxreqs.
– In AIX V6.1, there are two tunables for minservers and maxservers,
aio_minservers/aio_maxservers for older threads, and
posix_aio_minservers/posix_aio_maxservers for POSIX threads. Oracle uses
older threads.
– Increase aio_maxservers or posix_aio_maxservers Only by running ioo –p –o (the
default is 30 per logical CPU) if you run pstat -a | fgrep aio or ps -k | fgrep aio
shows that you are continually using maxservers.
– Oracle parameter (init.ora) should be set to disk_asynch_io = TRUE.