QUESTION:
I would like to know more about asynchronous I/O capability. The
parameters available on my Risc System/6000 w/AIX 3.2 shows MINIMUM
number of servers, MAXIMUM number of servers, maximum number of
REQUESTS, server PRIORITY and STATE to be configured. How do I
determine what are the 'best' values to use to improve my response time
and performance of the RISC running a database system which is expected
to use Asynchronous I/O?
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A: You want to have enough daemons running to handle the I/O
requests so that Sybase can continue to process without being
blocked waiting for I/O results. There will always be
MINIMUM number of daemons started. If there will be lots
of activity we want a higher minimum, but since each daemon
pinns memory, and pinned memory cannot be paged, we don't want
to have more daemons running than we need. For a starting
point try MINIMUM = number of disks 1,and MAXIMUM = MINIMUM + 5
I would leave the priority at 39.
Since the default priority is (40+nice), these daemons will be
slightly favored with this value of (39+nice). If you want to
favor them more, make changes slowly. A very low priority can
interfere with the system processes that require low priority.
Change the state to available.
As for tuning the best number: take statistics "vmstat -s"
before running your queries, and again at the end. Check the
field "iodone". From this you can determine how many physical
I/O's are being handled in a given wall clock period.
Then change the number of daemons running, and see if you can
get more iodones in the same time period. Also monitor
vmstat output to make sure the increase in daemons is not
increasing the amount of paging: pi, po, fr, sr.
Also watch the statistics from "svmon -G".
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This item was created from library item Q653904 CPVRJ
Additional search words:
AIX ALTERNATE ASYNCHRONOUS CPVRJ INDEX INPUT IO IX MAR94 MEASURE OP
OUTPUT OZNEW PERFORMANCE RISC RISCPERF RISCSYSTEM SOFTWARE SYS S6000
TUNE
WWQA: ITEM: RTA000039516 ITEM: RTA000039516
Dated: 03/1996 Category: RISCPERF
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