Re: Оцените производительность.

Главная Форумы POWER Systems AIX/Hardware Оцените производительность. Re: Оцените производительность.

#12986
Alex Kovalev
Участник

У нас тоже везде включен. Специально каких либо тестов показывающих влияния данного параметра на производительность не проводили. С одной стороны потому что продуктив весь на vxfs, а тестовые среды как правило по нескольку штук на одном томе (страйпе) в пределах LPAR. Если интересно попробовать, то ниже описание, которое вы наверное уже читали или видели.
I/O subsystem performance considerations
It is recommended that MWC be turned on for most logical volumes to insure data integrity and minimize
the data synchronization time after a system crash. If this leads to I/O performance problems, the traditional
methods of database tuning should be applied first. This includes topics like application design, database parameterization, datafile layout, etc. The ultimate goals are to avoid unnecessary I/O and then to spread
the remaining I/O evenly over all available physical disks. The disk subsystem performance can be
monitored with the standard tools like iostat and filemon. A disk should be investigated more
closely if iostat constantly shows a disk utilization of more than 15-20%.
Filemon can be used to determine the most active logical volumes and datafiles on that disk, the results
can then be compared with the Oracle v$filestat statistics for verification. The next step might be to move
some heavily used objects from these datafiles out into their own tablespaces and datafiles, or to separate
two actively used datafiles on their own disks.
If the database system still suffers from the write performance penalty associated with MWC, you might
decide to turn MWC off for selected logical volumes. Remember that Oracle tries to do all writes and some
reads (e.g. table scans) asynchronously to the application. Even though iostat shows a high disk utilization
rate, this may not be adversely affecting end user or response time performance. If you plan to turn MWC
off, first move datafiles with heavy write activity into their own filesystems. Then implement a procedure
to synchronize the mirror copies of these filesystems in the event of a system crash. Then, you can safely
turn MWC off.
It is recommended to leave MWC on for “read-only” and “read-mostly” filesystems as the MWC setting is
irrelevant for reads.