Thanks Tanel for the information. It too much asking but For #1 . Can you please elaborate or give example for this in which situation we will be waiting for new session to be created. #2. Can you please explain more on "You can still ask latches with other (lower) levels in no-wait mode and I think there also some special cases involved." On Sat, Jul 11, 2009 at 5:38 AM, Tanel Poder <tanel@xxxxxxxxxx> wrote: > 1. Session allocation latch is taken when a new session is about to be > created by a process and we need to find & allocate a slot from session > state object array (v$session). There's also a process allocation latch for > allocating process state objects from v$process array. > > 2. Latch level is used for internal purposes, for detecting and avoiding > possible latch deadlocks. Ideally this wouldn't be needed, but as there are > bugs in software then the latch level assertion allows a problem latch get > to fail with ORA-600 instead of causing a potential deadlock. When holding a > latch with level X, you can only request with level greater than X in > willing to wait mode. You can still ask latches with other (lower) levels in > no-wait mode and I think there also some special cases involved... > > 3. One way to find out what block type IDs mean is this: > > SQL> select view_definition from v$fixed_view_definition where view_name = > 'GV$WAITSTAT'; > > VIEW_DEFINITION > -------------------------------------------------- > select inst_id,decode(indx,1,'data block',2,'sort > block',3,'save undo block', 4,'segment > header',5,'save undo header',6,'free > list',7,'extent map', 8,'1st level bmb',9,'2nd > level bmb',10,'3rd level bmb', 11,'bitmap > block',12,'bitmap index block',13,'file header > block',14,'unused', 15,'system undo > header',16,'system undo block', 17,'undo > header',18,'undo block'), count,time from > x$kcbwait where indx!=0 > > > -- > Tanel Poder > http://blog.tanelpoder.com > > > On Sat, Jul 11, 2009 at 7:14 AM, Taral Desai <taral.desai@xxxxxxxxx>wrote: > >> Hi All, >> Can you please make me understand below things. >> >> 1. What is *LATCH*.*session allocation. We are seeing this in one of our >> RAC environment for Jobs* >> *2. What is v$latch.level. What is this used for.* >> *3. Not regarding latch but how to get data block type list. I know >> julian had mention on his site but how do we get this from database. >> * >> -- >> >> Thanks & Regards, >> Taral Desai >> Shelley >> Winters<http://www.brainyquote.com/quotes/authors/s/shelley_winters.html> - >> "Whenever you want to marry someone, go have lunch with his ex-wife." >> > > > > -- > Tanel Poder > http://blog.tanelpoder.com > > -- Thanks & Regards, Taral Desai Gilda Radner <http://www.brainyquote.com/quotes/authors/g/gilda_radner.html> - "Adopted kids are such a pain - you have to teach them how to look like you."