Examine the following details from the AWR report for your three-instance RAC database:
Which inferences is correct?
A.
There are a large number of requests for cr blocks or current blocks currently in progress.
B.
Global cache access is optimal without any significant delays.
C.
The log file sync waits are clue to cluster interconnect latency.
D.
To determine the frequency of two-way block requests you must examine other events In the
report.
Explanation:
Analyzing Cache Fusion Transfer Impact Using GCS Statistics
This section describes how to monitor GCS performance by identifying objects read and modified
frequently and the service times imposed by the remote access. Waiting for blocks to arrive mayconstitute a significant portion of the response time, in the same way that reading from disk could
increase the block access delays, only that cache fusion transfers in most cases are faster than
disk access latencies.
The following wait events indicate that the remotely cached blocks were shipped to the local
instance without having been busy, pinned or requiring a log flush:
gc current block 2-way
gc current block 3-way
gc cr block 2-way
gc cr block 3-way
The object statistics for gc current blocks received and gc cr blocks received enable quick
identification of the indexes and tables which are shared by the active instances. As mentioned
earlier, creating an ADDM analysis will, in most cases, point you to the SQL statements and
database objects that could be impacted by interinstance contention.
Any increases in the average wait times for the events mentioned in the preceding list could be
caused by the following occurrences:
High load: CPU shortages, long run queues, scheduling delays
Misconfiguration: using public instead of private interconnect for message and block traffic
If the average wait times are acceptable and no interconnect or load issues can be diagnosed,
then the accumulated time waited can usually be attributed to a few SQL statements which need
to be tuned to minimize the number of blocks accessed.
Oracle Real Application Clusters Administration and Deployment Guide
11g Release 2 (11.2)
http://www.slideshare.net/oracleil/rac-performance-tuning-iloug
slide 25
A is wrong. no gc cr buffer busy event
B is right. gc current block 3-way is 1ms average
C is wrong. log file sync is clue to too many commits
D is wrong. no 2-way block requests
So B is correct
Incorrect question (I found it in other tests):
Which TWO inferences are correct?
Answer: A, C