Henry,
I'll make an attempt, but I am still learning a great deal about wait events
and trace files. Cary, Mogens, Anjo, Tim, Jonathan, Wolfgang, et.al. are better
authorities, so any corrections are very welcome.
The time between waits is the elapsed time. If we equate elapsed time to
response time, we must look at the two components of RT, wait time and service time.
If the time differential is 7 minutes, x minutes is service time and y minutes is wait
time. It is possible that only .01 seconds was wait time, while the remaining 6:59:99
was service time (i.e. cpu)
I can't explain the scattered read issue. However, it is interesting to note
that the # of blocks to be read is offset by 1 in the second wait event. Perhaps, the
read request was issued, but the 65.6041 block was already in memory, so the read
request was reissued minus that block. I'm not sure how the latch free enters into the
picture, but I have a feeling that this wait is integral in the sequence of events.
Dan
Henry Poras wrote:
>
> (Tried sending this yesterday. I'll try again)
>
> Dan,
> I was running a 10046 (level 12) trace on an awful piece of PeopleSoft SQL
> today and got some really odd results in my trace file (8.1.7).
>
> *** 2003-07-23 15:40:59.149
> WAIT #1: nam='db file scattered read' ela= 0 p1=65 p2=6041 p3=18
> *** 2003-07-23 15:46:06.340
> WAIT #1: nam='latch free' ela= 1 p1=813986232 p2=66 p3=0
> *** 2003-07-23 15:47:53.851
> WAIT #1: nam='db file scattered read' ela= 0 p1=65 p2=6042 p3=17
>
> Two things struck me (three if it takes me too long to write this and I get
> home late). First, the timestamps show an elapsed time of ~7 minutes, but
> the trace file has ela=1 (one onehundredth of a second). The 7 minutes is
> closer to reality. Huh???
>
> Secondly, the first scattered read reads 18 blocks starting at 6041. Why
> does the next scattered read start at block# 6042?
>
> Any ideas?
>
> Henry
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