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 child latch. The latch allows a process to scan a hash chain without having the linked list change while it scans. Problem: High or rapidly increasing wait counts on the CACHE BUFFERS CHAINS latch is an indication that the latch is not able to service the different sessions fast enough. Contention for these latches can be caused by very heavy access to a single block or heavy concurrent execution of poorly written SQL statements which touch too many blocks (i.e. same blocks). This latch used to be big problem in Oracle7 and Oracle8i. In Oracle9i, operations on this latch have been optimized significantly. Analysis: Once a buffer chain contention problem has been identified , determine the object that the block belongs to.
本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1277885
