Author: mac

This is an Exadata wait event similar to db file sequential read and normally occurs during index lookups when the block is not in memory and must be read from the Exadata storage cell disks. These are generally considered a ‘good’ read unless the index being used is not very efficient. In this case the…

This is an Exadata wait event similar to ‘db file scattered read’ and typically indicates the statement is performing a full table scan or an index fast full scan. This wait event is not seen nearly as much as ‘db file scattered read’ is seen on non-Exadata platforms because many full scans are offloaded to…

This is an Exadata wait event that occurs when a storage cell is starting and opening a cell for use.     Solutions This is a normal part of starting up the storage cell in an Exadata system. If there are queries waiting on this, it means the storage cell has not yet started.

This is an Exadata wait event that occurs when a storage cell is starting and discovering disks.   Solutions This is a normal part of starting up the storage cell in an Exadata system. If there are queries waiting on this, it means the storage cell has not yet started.

This is an Exadata wait event that occurs during the shutdown of a storage cell. This is normal activity associated with shutdown processing.   Solutions If there are queries waiting on this event, it may indicate that your storage cell is in progress of shutting down and the query is forced to wait.

This is an Exadata wait event similar to ‘db file parallel read’ and normally occurs during multi-block reads of non-contiguous blocks. The most common operations associated with this wait event are index range scans, index unique scans and lookups by rowid. Solutions Review solutions for db file parallel read for more information.

Background A user process acquires this latch to scan the SGA for database cache buffers. Blocks in the buffer cache are placed on linked lists (cache buffer chains). Blocks are put on the hash chain according to their DBA (data block adress) and CLASS of the block. Each hash chain is protected by a single…

This latch is needed when user processes try to scan the LRU (least recently used) chain containing blocks in the buffer cache. This latch must be acquired before the block can be inserted into (when the block is read in from the disk) or taken out of the LRU chain (when the block is written…

Wait occurs when a session attempts to access a block in memory, is denied and must wait until the buffer becomes available. This event happens because a buffer is either being read into the buffer cache by another session (and the session is waiting for that read to complete) or the buffer is in the…

Wait is related to the sizing / usage of the CTWR dba buffer in the Large Pool memory structure more …       Solutions Problem: When a session waits on the “Block Change Tracking Buffer” event, it indicates that there was a wait for space in the CTRW dba buffer. If this happens too…