PerfMatrix 
What is Buffer Hit ratio OR Buffer Hit %? ‘Buffer Hit Ratio’ is measured by the percentage of times the data block is requested by the query and available in memory. It is also called the ‘Buffer-Cache Hit Ratio’. Effective use of the buffer cache can greatly reduce the I/O load on the database. If … Read more
What is Execute to Parse ratio OR Execute to Parse %? Every query needs to be parsed before it gets executed. If some queries are quite frequently used, a good design will be to reuse the parsed query. That means it will not parse the same query again. In an ideal world, execution should be … Read more
In AWR, the ‘Instance Efficiency Percentages’ table comes under the ‘Report Summary’ section. Refer to the below figure: The following metrics are available in the ‘Instance Efficiency Percentages’ table of an AWR report: Buffer Nowait % (Buffer Nowait Ratio) This metric provides the percentage of availability of the data buffers. This ratio gives an idea … Read more
In AWR, the Load Profile table comes under the ‘Report Summary’ section. Refer to the below figure: The following metrics are available in the Load Profile table of an AWR report: DB Time(s) DB Time(s) is the number of average active sessions during the given period. The active sessions are calculated by dividing the ‘DB … Read more
Following are the Performance Engineering Interview Questions Set #13. Q. 61 How can lock contention be identified in an AWR report? Ans: High wait events like “enq: TX- row lock contention” or “enq: TM- contention” indicate lock waits. The “Segments by Row Lock Waits” section shows which segments are involved. Q. 62 What does the … Read more
Following are the Performance Engineering Interview Questions Set #12. Q. 56 What role does the buffer cache play in database performance? Ans: The buffer cache stores copies of data blocks read from the disk. A properly sized buffer cache reduces physical I/O by satisfying requests from memory, thus improving performance. Q. 57 How can you … Read more