My current understanding is: a) For normal buffer gets, the latch is acquired, the chain is scanned the buffer is pinned the latch is released the buffer is used -- the latch is acquired the pin is dropped (although the pin may be held for the duration of the SQL or pl/sql call if Oracle expects to revisit the buffer)
b) Consistent gets - examination the latch is acquired the chain is scanned if the buffer can be found it read the latch is dropped Iin case (b), Oracle can make use of a shared read latch - where the underlying CPU supports it. But I may be wrong - especially about (b), and I haven't identified all the cases where an examination is legal. Question 2 - the best answers come from Steve Adams. But in summary, think library cache latch children - you may need to validate several objects in the library cache at once, and they could be covered by different child latches. Latches have a level#, from 0 to 9, and there is a precedence of latch acquisition across levels that is designed to stop latch acquisition deadlocks (again see S.A.). The holding of multiple latches also explains the presence of the column named (something like) waits_holding in v$latch. You have waited for this latch whilst holding another latch. Regards Jonathan Lewis http://www.jlcomp.demon.co.uk The educated person is not the person who can answer the questions, but the person who can question the answers -- T. Schick Jr One-day tutorials: http://www.jlcomp.demon.co.uk/tutorial.html Three-day seminar: see http://www.jlcomp.demon.co.uk/seminar.html ____UK___November The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html ----- Original Message ----- To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]> Sent: Wednesday, December 03, 2003 4:19 AM Hi All, My system is suffering in cache buffer chain,I found the reason. My general questions is 1) When the process holding the latch how long the latch will be held ,until the hase chain is read or the process goes to the particular block and return the rows(output) ? 2) When the situation will occur for the process to hold two latches(different or same) simultaneously ? Please reply. Syed. -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jonathan Lewis INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).