A session waits on this event when it is requesting a mutex in shared mode, when another session is currently holding a this mutex in exclusive mode on the same cursor object. Parameter Description P1 Hash value of cursor P2 Mutex value (top 2 bytes contain SID holding mutex in exclusive mode, and bottom two…
Reading from the control file. This happens often. For example, while: Making a backup of the control files Sharing information (between instances) from the control file Reading other blocks from the control files Reading the header block Wait Time: The wait time is the elapsed time of the read Parameter Description file# The control file from…
This event occurs while the session is writing physical blocks to all control files. This happens when: The session starts a control file transaction (to ensure the control files are up to date in case the session crashes before committing the control file transaction) The session commits a transaction to a control file Changing a generic…
When a process spawn is aborted while the process spawning background is in the middle of spawning, the current session must wait until the pid of the new process is filled in. Once the pid is filled in, then the process spawn can be actually aborted.
A session waits for a checkpoint to complete. This could happen, for example, during a close database or a local checkpoint.
This event occurs only if the instance is mounted in shared mode (Oracle Real Application Cluster). During the read of the buffer, the contents changed. This means that either: The version number, dba, or the incarnation and sequence number stored in the block no longer match The checksum on the block does not match the…
The session waits on the buffer hash chain latch. Primarily used in the dump routines. The virtual address in the SGA where this latch is located. Use the following statement to find the name of this latch: select * from v$latch a, v$latchname b where addr = latch addr and a.latch# = b.latch#; chain# The…
Oracle does not really wait on this event; the foreground only yields the CPU. Thus, the chances of catching this event are very low. This is not an application induced deadlock, but an assumed deadlock by the cache layer. The cache layer cannot get a buffer in a certain mode within a certain amount of…
This article is part of Oracle Performance Tuning Series and is created to describe Oracle’s locking mechanism. A lock is a resource that you need to hold to get access to the resource. Oracle has two kind of locks: enqueues and latches, we would now focus on these locking mechanism individually. Enqueues Enqueues are sophisticated…
If you performed lot of DMLs (specially Deletes) on a table, you may have lots of empty leaf blocks in the associated indexes on that table. These empty leaf blocks are left in the b-tree structure AND attached to the freelist. On subsequent inserts, the process might need to split a block so it takes…
Oracle Database Internal Mechanism 