RE: Wait events
- From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 2 May 2004 21:29:53 -0500
The term "wait event," which Oracle Corporation chose to use long ago in
the Oracle7 documentation set, has caused a great deal of confusion. It
has led many authors to [mis]believe that a wait event's duration must
consist of only the time spent queued for some resource. Not true. It is
*NOT* the 'W' in the queueing theory equation "R = S + W".
The duration of a "wait event" is the time that elapses between some
time t0 when the Oracle kernel makes one gettimeofday call until some
later time t1 when the Oracle kernel makes another gettimeofday call.
Usually in between, the Oracle kernel issues a single OS call (read,
write, sleep, etc.), although there are some situations in which the
kernel makes two or more syscalls in the context of a single "wait"
(seek+read, for example). So the duration of a "wait event" includes all
time spent making the syscall, which includes service time and any
queueing delay that was incurred for the requested resource (plus the
duration of one gettimeofday call, but that's a minor detail).
Thankfully, the 10g documentation calls them "timed events" instead of
"wait events." They're still the same thing they ever were. But now they
have a less confusing name.
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Michael Brown
Sent: Monday, May 03, 2004 8:02 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Wait events
Simply put an Oracle wait event is what the kernel is doing at that
point in time for the session you are tracking. To understand how this
applies to performance, get a copy of Cary Millsap's book.
http://www.amazon.com/exec/obidos/tg/detail/-/059600527X/
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Computer Centre -
NIIPL
Sent: Monday, May 03, 2004 1:21 AM
To: ORALCE LIST
Subject: Wait events
Dear All,
Please help me know about Oracle wait events and its implication in
Oracle Performance. Thanks in Advance, Regards, Balu This mail is scaned
by eScan Anti Virus Software
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