Latches and Tuning:Latches

1. Query the V$FIXED_TABLE to determine the V$ views that provide latch information.

a. Execute the following query:> select name from v$fixed_table where name like 'V$LATCH%';

2. Remember that there are 14 levels of latches, numbered 0 �C 13.

a. Take a look at three common latches and their level by executing the following query:> select name, level# from v$latch where name in ('cache buffers chain','library cache','redo allocation'); You may or may not see each of these latches listed depending upon the state and activity on your database.

3. Each parent and child latch has one instance in X$KSLLT.

a. Execute the following query to view a KSLLT structure for a latch:> select v$latch_parent.addr,v$latch_parent.level#,v$latch_parent.latch#, v$latch_parent.name from v$latch_parent,x$ksllt where v$latch_parent.addr = x$ksllt.addr; You should at least see information for the ‘latch wait list’ latch. However, your results will vary depending upon the state and activity of your database.

4. Using the latch# from the previous query, you can query the X$KSLLD table to see the array of latch descriptors.