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oracle :latch: cache buffers chains

原创 Linux操作系统 作者:gluyuan 时间:2011-05-13 10:18:14 0 删除 编辑


Top 5 Timed Events                                                    Avg %Total
~~~~~~~~~~~~~~~~~~                                                   wait   Call
Event                                            Waits    Time (s)   (ms)   Time
----------------------------------------- ------------ ----------- ------ ------
PL/SQL lock timer                                3,181       3,336   1049   55.3
CPU time                                                     2,466          40.9
latch: cache buffers chains                        701          80    114    1.3
log file parallel write                          3,366          64     19    1.1
library cache pin                                  601          32     53


The latch: cache buffers chains Oracle metric are used to protect a buffer list in the buffer cache. These latches are used when searching for, adding, or removing a buffer from the buffer cache. Contention on this latch usually means that there is a block that is greatly contended for (known as a hot block).

Rich Niemiec notes on latch cache buffer chains:

"Latches are like locks on memory that are very quickly activated and released by a process, and they are used to prevent concurrent access to a shared-memory structure.

If the latch is not available, then a latch-free miss is recorded. Most latch problems are related to not using bind variables (library-cache latch), redo-generation issues (redo-allocation latch), buffer-cache contention issues (cache-buffers LRU條east recently used梒hain), and hot blocks in the buffer cache (cache-buffers chain)."



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