Can you describe the hit ratio in the context of database buffers? Also, do you use the instantaneous or cumulative hit ratio for tuning?

When asked a two-part question, you should respond similarly. Start by answering the first part, then answer the second part of the question. As with any technical or operational question, your answer should be brief and to the point. You should also anticipate follow-up questions from the interviewer.

"In the context of database buffers, the hit ratio provides information about how many times the database could read a value from the buffers instead of how many times it had to re-read a data value from the disks. The higher the percentage of reads from the buffers, the better the database performs. Anything less than 80% buffer reads indicates that there is a problem. A hit ratio of existing parameters is a cumulative value since the database started. It is not as accurate as the instantaneous hit ratio, which compares pairs of readings based on a designated time span. I prefer the instantaneous hit ratio for tuning since it provides more valuable data by indicating what the instance is doing over the time it was generated."