Following are the Performance Engineering Interview Questions Set #16.
Q. 76 Explain the “latch: cache buffers chains” wait event and its impact.
Ans: This wait event indicates contention for cache buffer chain latches, which protect the hash chains of buffer headers in the buffer cache. High waits suggest hot blocks or heavy concurrent access to specific buffers.
Q. 77 How can “latch: cache buffers chains” contention be alleviated?
Ans: Identify hot blocks using VSBH and VSCACHE and spread out access by partitioning data, optimizing SQL to access data less frequently, or adding indexes to reduce unnecessary full scans.
Q. 78 What is the significance of the “library cache lock” wait event?
Ans: It indicates contention in the library cache, often due to high parsing rates, invalidations, or concurrent DDL operations. This can lead to increased CPU usage and slower query performance.
Q. 79 How can you address “library cache lock” waits?
Ans: Reduce hard parsing by using bind variables, minimize DDL operations during peak times, and ensure the shared pool is adequately sized.
Q. 80 What does the “Instance Efficiency Percentage” section of the AWR report represent?
Ans: It represents how efficiently the database instance is operating, such as buffer cache hit ratio, library cache hit ratio and parse ratio.
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