OCP question analysis _ 043: buffer cache and hit rate

OCP question analysis _ 043: buffer cache and hit rate calculation method: www.2cto.com SELECT name, (1-(physical_reads/(db_block_gets + consistent_gets) * 100 H_RATIO FROM v $ ratio; the hit rate, as the standard for measuring the performance of the database, is already an old man's experience. Today, the hit rate can be used as a reference through the oracle wait interface, but the hit rate is not necessarily related to the system performance level, it is only one side and the single-view hit rate. In many cases, the problem cannot be explained. It is best to compare it with the previous one to view data from OLTP to OLAP at a certain time point every day, some operations are performed to scan all tables. At this time, the number of physical reads increases ,............, If the hit rate is low for this period of time every day and there is no valuable wait event, there will be no performance problem www.2cto.com for the time being. So, don't pay too much attention to the hit rate parameter! If the hit rate is not very good, but the performance is still good, you can ignore it. It depends on whether the user is satisfied! If the buffer cache is too smalll for your system, you will see "free buffer waits" in the v $ system_event table. and that is the better place to check. if the hit rate is indeed very low, you may try to check Top N (SQL or Event). The following uses Top SQL as an example to find that there are many Top SQL methods, the most common method is to search for Top SQL in the statspack report. In addition, the OEM Top SQL tool oem SQL Aanlyzer 10gADDM can also sort Top SQL based on the influence of SQL on the system, after finding Top SQL, you can use the Optimization Wizard to optimize and analyze OCP questions: [SQL] 1.You observe that a database performance Has degraded over a period of time. while investigating the reason, you find the size of the database buffer cache is not large enough to cache all the needed data blocks. which advisory component wold you refer to, in order todetermine that required size of the database buffer cache? A. Memory Advisor B. Segment Advisor C. SQL Tuning Advisor D. SQL Access Advisor E. Automatic Database Diagnostic Monitor (ADDM) Answer: