CompTIA DataSys+ (DS0-001)Database Management and MaintenanceEasy
A database administrator is setting up monitoring for a new production database. They need to track the percentage of data blocks found in the database's memory cache (buffer cache) versus those read from disk. This metric is crucial for understanding how effectively the database is utilizing memory to avoid slow disk I/O. Which metric should they prioritize monitoring?
- ADisk queue length.
- BTransaction per second (TPS).
- CCPU utilization percentage.
- DBuffer cache hit ratio.
Show answer & explanationAnswer & explanation
Correct answer: D. Buffer cache hit ratio.
The buffer cache hit ratio directly measures the percentage of data blocks found in memory (buffer cache) without needing to access slower disk storage, making it the ideal metric for assessing memory utilization effectiveness.
Why the other options are wrong
- A. Disk queue length indicates pending disk I/O requests, which can be an *effect* of poor buffer cache utilization, but not the direct measure of it.
- B. TPS measures database throughput but doesn't specifically indicate buffer cache effectiveness.
- C. CPU utilization measures processor activity but not specifically how memory is used for data blocks.
Buffer Cache Hit Ratio
A performance metric that indicates the percentage of data blocks requested by the database that were found in the buffer cache (memory) rather than having to be read from disk.
- Higher ratio indicates better memory utilization and less disk I/O.
- A crucial indicator of database performance.
- Calculated as (Buffer Cache Reads / Total Reads) * 100.
Memory trick: How often does the brain (buffer) 'hit' the right answer?