Question

The read efficiency is the percentage of times a data page is found in the data cache memory (or buffer pool) without requiring a physical I/O. How do you trace the read efficiency records and what factors impact this percentage?

Answer 1

Read Efficiency of the data cache is a percentage, which tracks how well the cache is perfoming its job to avoid physical or IO operations. The read efficiency of each data is caclulated as difference of total number of data requests and number of actual I/Os performed then divided by the total number of requests. We can write it as

Read Efficiency = ((Number of Database I/O requests)-(Number of Physical I/O s) ) /

(Number of database I/O requests)

We can trace the read efficiency records by examining the actual numbers for I/O(Input/ Output) requests and actual Physical I/O operations in the DBMS trace records or by using database performance monitor

The following factors impact read efficiency percentage.

1) Anticipation of I/O requirements and scheduling reads of multiple blocks prior to request for processing. Good anticipation brings good performance.

2) Read efficiency value depend on the type of processing.

3) Many sequential processes can cause the data cache to be overrun and the efficiency to drop.

4) Systems with many processes that access data only weeklu or monthly may have lower read efficiencies because less data is frequently reused

5) The number or type of concureent processes using the data cache.