Re: Researching latch efficiency
Date: Sat, 28 Jun 2008 21:45:23 +0200
Symptoms vs problems. Latch waits are always symptoms of the real problem. So this particular latch is a symptom because the shadows sending many messages to the background processes. Normally this would be LGWR and/or the DBWR. Dumping the messages (oradebug dump messages and x$message have the answers). Hmmm didn't I do a presentation on this 3-4 years ago during IOUG :)
Op 6/21/08 3:21 PM, Yong Huang <yong321_at_yahoo.com> schreef:
> Anjo Kolk's wait event article is still the most complete about documenting
> latches. Search for it on Google.
> There is a pool of message blocks in the SGA. This pool is controlled by the
> init.ora parameter _messages. If a process needs a message it will get the
> latch, search a linked list for a free message block, unlink this message
> , put this message on the message queue for the intended process and then
> release this latch. The event rdbms ipc message indicates that a process is
> waiting for a message to arrive on his message queue. The event rdbms ipc
> message reply is used to indicate that a message is expected back by the
> sending process.
> Why not compare the numbers in Spotlight and sqlplus? If they're close, they
> must be referring to the same event.
> Yong Huang
>> I'm using Quest's Spotlight and wonder if it means "latch: messages". I >> may need to open a ticket with Quest Support to explain the display in >> their GUI. >> >> Not sure if this is the one I'm waiting on. I'll look deeper. >> >> sql> select * from v$event_name where name = 'latch: messages'; >> >> The online Oracle doc referenced by Jared (thanks J!) does not have all >> 889 wait events documented for 10.2.0.4. I doubt I'm gonna find it. :-)
Received on Sat Jun 28 2008 - 14:45:23 CDT