Re: [evlog-dev] evlog and db2

Question #1: evlview --new uses posix_log_notify() because posix_log_read()
never blocks.  Neither does posix_log_seek(), which is pertinent if you
want only selected records.  So you have to explicitly sleep() or pause()
while waiting for the next record.  The non-blocking nature of
posix_log_read() can be a pain, but it's been in the POSIX spec since
God-knows-when.

Question #2: As I mentioned in previous (private) mail, I'd expect the
plug-in technique to be faster.  I just ran a little benchmark.  On my
laptop, I could log about 3800 NODATA events per second without evlview
--new running.  This dropped to about 2340 events per second with evlview
--new running.  (evlview managed to catch all the events, but evlogd simply
logged fewer of them.)  I attribute most of the difference to the
notification overhead; presumably, evlogd had to spend more time waiting
for evlnotifyd.

Jim


|---------+-------------------------------------------->
|         |           Mark Megerian/Rochester/IBM@IBMUS|
|         |           Sent by:                         |
|         |           [email protected]|
|         |           ceforge.net                      |
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|         |                                            |
|         |           03/05/03 02:18 PM                |
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  |       To:       [email protected]                                                                                           |
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  |       Subject:  [evlog-dev] evlog and db2                                                                                                        |
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I have made good progress with getting the evlog data into a db2 table.  In
looking through the code in evlview for getting notified of new events, I
was puzzled by something.

I suspect this is a naive question, but:

- The code uses posix_log_notify_add to ask to be notified about new
events, but then it uses posix_log_read to process all of the events.  To
the uninitiated, that seems like a contradiction.  Why ask to be notified,
if you are essentially going to loop on reading the log for new events
anyway?  Is it because there is a level of indirection between the evlog
event, and this posix log??

Also, I am interested in getting any opinions on the performance
expectations of using this notify technique vs. the plug-in technique.
Expecting to have a large volume of events over 1,024 nodes, so pathlength
is important.


thanks!



Mark Megerian    (507) 253-1682
[email protected]




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