Extremely High V_$SYSTEM_EVENT Wait Times on Oracle DB

oracleperformance

I'm working on troubleshooting an oracle DB that's having some general performance problems. I ran the following query:

SELECT event AS "Event|Name",
       total_waits "Total|Waits",
       round(time_waited / 100, 0) "Seconds|Waiting",
       total_timeouts "Total|Timeouts",
       average_wait / 100 "Average|Wait|(in secs)"
  FROM sys.v_$system_event e
  ORDER BY time_waited DESC;

The first few lines returned as follows. Millions of seconds of wait time! (By comparison our other DBs are < 10 seconds of wait time for the top events.) What do these events do and what could cause these massive wait times? The DB has been up for 30 days so we're seeing aggregation over that much time.

Event Name                                 Waits    Seconds Timeouts  Avg Wait
----------------------                 ---------   -------- --------  --------
SQL*Net message from client            488397968   32050594        0    0.0656
rdbms ipc message                       91335556    2455744  9529486    0.0269
DIAG idle wait                           5214769     347077  5214769    0.0666
Streams AQ: qmn coordinator idle wait     186521     173696    93278    0.9312
Streams AQ: qmn slave idle wait            95359     173692       51    1.8215
Space Manager: slave idle wait            523165     173647   521016    0.3319
pmon timer                                968303     173630   870108    0.1793
fbar timer                                  8770     173403     8713   19.7723
smon timer                                 14103     173278     7006   12.2866
log file sync                           57967889      90402   649458    0.0016
og file parallel write                  86618366      39509        0    0.0005
db file sequential read                244286101      11171        0         0
control file parallel write              1274395       3949        0    0.0031
db file scattered read                 157316868       1635        0         0
db file parallel read                   11948170       1190        0    0.0001

Best Answer

"SQLNet message from client" is the time spent by the database waiting to be asked to do something by a client (I would also interpret this to be an indicator of the number of SQLNet requests processed by the database). AskTom has more information about the event. It doesn't look like a very long average wait, either, so perhaps you've got an app that's making LOTS of small requests to the server? That's a lot of waits in 30 days (average of 16M per day).

As for the rdbms ipc message, this means (Oracle 10g Reference):

"The background processes (LGWR, DBWR, LMS0) use this event to indicate that they are idle and are waiting for the foreground processes to send them an IPC message to do some work."

This is generally a non event from a tuning perspective. (Burleson)

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