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Data Guard redo configuration asynchronous mode, the Log Network Server (LNS) process will attemp to read redo directly from the log buffer. If the redo to be sent is not found in the log buffer, then the LNS process will go to the Online Redo Log (ORL) to retrieve it. Size the log buffer so that LNS is always able to find the redo that is needs to send within the log buffer. The log buffer hit ratio is tracked in the view x$logbuf_readhist . A low hit ratio indicates that the LNS is frequently reading from the ORL instead of the log buffer. If there are periods when redo transport is coming close, but is not quite keeping pace with your redo generation rate, consider increasing the log buffer size in Data Guard 11g to achieve a favorable hit ratio.

In 11gR2, Oracle has introduced a new registry to maintain the clusterware resources (css, crs,evm,gip and more) in a new registry called Oracle Local Registry (OLR) . Multiple processes on each node have simultaneous read and write access to the OLR particular to the node on which they reside, regardless of whether Oracle Clusterware is running or fully functional. By default, OLR is located at Grid_home/cdata/host_name.olr on each node.The OCR still exists, but maintains only the cluster resources. Until Oracle Database 11gR1, the RAC configurations consisted of just one registry when running Oracle Clusterware. Shortly called OCR, Oracle Cluster Registry, maintained the cluster level resource information, privileges etc. To be precise, the OCR maintained information about 2 sets of node level resources, namely, the Oracle Clusterware Components (CRS, CSS, evm) as well as Cluster resources (DB, Listener etc).