RE: MMAN blocker
- From: Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>
- To: Stefan Koehler <contact@xxxxxxxx>, "ORACLE-L (oracle-l@xxxxxxxxxxxxx)" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 12 Sep 2019 13:03:18 +0000
Hi Stefan,
=> So if I've understood correctly, you're suggesting that the MMAN might
have waited on a semaphore held by some other process?
I was trying to figure out if MMAN got/send some notification via semaphore
or if some other processes were involved in IPC communication at all ("The
pid column identifies the most recent process to complete a semaphore
operation."). Not quite sure if semaphore posts are always guaranteed to
arrive nowadays (or the mess of crashed processes, etc. is cleaned up
properly) - wanted to go a little bit deeper here with it :-)
Just a little side note: on Solaris, Oracle database uses "event completion
framework" (
https://blogs.oracle.com/dap/libevent-and-solaris-event-ports ;)
instead of semaphores for notifications. I traced Oracle C functions handling
notifications and saw that they're underpinned by port* instead of sem* OS
kernel functions. Of course, your remarks about semaphores apply to "event
completion framework" too.
Best regards,
Nenad
https://nenadnoveljic.com/blog/
-----Original Message-----
From: Stefan Koehler <contact@xxxxxxxx>
Sent: Donnerstag, 25. Juli 2019 16:07
To: Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>; ORACLE-L
(oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
Subject: RE: MMAN blocker
Hello Nenad,
=> So if I've understood correctly, you're suggesting that the MMAN might
have waited on a semaphore held by some other process?
I was trying to figure out if MMAN got/send some notification via semaphore or
if some other processes were involved in IPC communication at all ("The pid
column identifies the most recent process to complete a semaphore operation.").
Not quite sure if semaphore posts are always guaranteed to arrive nowadays (or
the mess of crashed processes, etc. is cleaned up properly) - wanted to go a
little bit deeper here with it :-)
=> But then why ORA-04031 flood, in the first place? According to the system
dump there was plenty of free memory to fulfill the request, at least at some
point. The scenario of not being able to find consecutive 40 bytes seems
rather unlikely.
Sorry I may got your question wrong but I thought you wanna know what kind of
action triggers MMAN as you wrote "How does a session makes a decision whether
to allocate a chunk from the free memory or to wait on 'SGA: allocation forcing
component growth'?". Seems like it was not or there is a bug for finding free
space :-)
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website:
http://www.soocs.de
Twitter: @OracleSK
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