<div style="font-family:微软雅黑;font-size:14px;line-height:21px;white-space:normal;widows:auto;background-color:#FFFFFF;"> <div> <span style="font-family:Arial;">&nbsp; &nbsp; Cache Fusion basically is about<span style="background-color:inherit;">&nbsp;</span></span><span style="color:red;font-family:Arial;">fusing the memory buffer cache of multiple instance into one single cache.</span><span style="font-family:Arial;"><span style="background-color:inherit;">&nbsp;</span>For example if we have 3 instance in a RAC which is using the same datafiles and each instance is having its own memory buffer cache in their own SGA, then cache fusion will make the database behave as if it has a single instance and the total buffer cache is the sum of buffer cache of all the 3 instance. Below figure shows what I mean.</span><br style="background-color:inherit;" /> </div> <div> <span style="font-family:Arial;"><br style="background-color:inherit;" /> </span> </div> <div> <span style="font-family:Arial;">&nbsp; &nbsp; 缓存融合是指将多个实例的内存缓存融合到一个实例的缓存中。例如，如果我们在一个使用同相同数据文件RAC集群中有三个实例，每个实例在他们自己的SGA中有自己的buffer cache。那么，cache fusion 会使数据库表现如下：有一个实例的全部buffer cache是3个实例大小的总和。</span> </div> <div> <img data-media-type="image" src="file://D:/%E6%9C%89%E9%81%93%E4%BA%91%E7%AC%94%E8%AE%B0/%E6%95%B0%E6%8D%AE%E7%9B%AE%E5%BD%95/zr2095@163.com/b5a43bbc10e744bb811e3ead5f481532/1.gif" data-attr-org-src-id="1D54D0612A4A4DA49149CC8051CB9330" data-attr-org-img-file="file:///D:/%E6%9C%89%E9%81%93%E4%BA%91%E7%AC%94%E8%AE%B0/%E6%95%B0%E6%8D%AE%E7%9B%AE%E5%BD%95/zr2095@163.com/b5a43bbc10e744bb811e3ead5f481532/1.gif" style="background-color:inherit;cursor:default;display:inline-block;margin-top:8px;max-width:800px;" /> </div> <div> <span style="font-family:Arial;"><img src="/attachment/201510/15/30208428_1444872270e9VP.gif" width="494" height="325" alt="" /><br style="background-color:inherit;" /> </span> </div> <div> <span style="font-family:Arial;"> <p> <span style="background-color:inherit;color:red;">&nbsp; &nbsp; This behavior is possible because of high speed interconnect existing in the cluster between each instance.</span><span style="background-color:inherit;">&nbsp;</span>Each of instance is connected to other instance using a high-speed interconnect. This makes it possible to share the memory between 2 or more servers. Previously only datafile sharing was possible, now because of interconnect, even the cache memory can be shared. </p> <p> &nbsp; &nbsp; &nbsp;这个表现可能是由于高速内部连接存在于集群中的每个实例。每个实例使用高速内部连接来连接到其他的实例。这就使得可以在2个或者更多的服务器上共享内存。以前是有数据文件能够共享，现在由于内部连接，甚至是内存缓存也能被共享了。 </p> <p> <br /> </p> <p> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; But how this helps? Well, for example if we have a data block in one of the instance and its updating the block and other instance needs the same data block then this data block can be copied from holding instance buffer cache to requesting instance buffer cache using this high-speed interconnect.<span style="background-color:inherit;">&nbsp;</span><span style="background-color:inherit;color:red;">This high speed interconnect is a private connection made just for sending data blocks and more by instances.</span><span style="background-color:inherit;">&nbsp;</span>External users cannot use this connection. It is this interconnect which makes multiple server behave like a cluster.<span style="background-color:inherit;">&nbsp;</span><span style="background-color:inherit;color:red;">These servers are bind together using this interconnect.</span> </p> <p> &nbsp; &nbsp; &nbsp;但是这个有什么帮助呢？例如，如果我们在其中一个实例中有一个数据块和它正在更新的块，其他的实例需要同一个数据块，那么这个数据块能够使用高速内部连接从持有这个块的buffer cache复制到请求实例的buffer cache。这个高速连接是一个私有连接，被实例用来发送数据或者其他的内容。外部用户不能使用这个连接。正是这个内部连接使得多个服务器表现得像一个集群。多个服务器通过这个内部连接被绑定在一起。 </p> </span> </div> <br style="background-color:inherit;" /> </div> <div style="font-family:微软雅黑;font-size:14px;line-height:21px;white-space:normal;widows:auto;background-color:#FFFFFF;"> Cache Fusion简单示例 </div> <div style="font-family:微软雅黑;font-size:14px;line-height:21px;white-space:normal;widows:auto;background-color:#FFFFFF;"> <br /> <img src="/attachment/201510/15/30208428_1444872293T979.png" width="623" height="473" alt="" /><img src="/attachment/201510/15/30208428_1444872293bv1U.png" width="623" height="473" alt="" /><img src="/attachment/201510/15/30208428_1444872293QkrO.png" width="623" height="473" alt="" /><img src="/attachment/201510/15/30208428_144487229411pg.png" width="623" height="473" alt="" /><img src="/attachment/201510/15/30208428_14448722943F0q.png" width="623" height="473" alt="" /><br style="background-color:inherit;" /> </div> <div style="font-family:微软雅黑;font-size:14px;line-height:21px;white-space:normal;widows:auto;background-color:#FFFFFF;"> <br /> </div>