10. Databases

DTrace is a powerful tool for analyzing databases, allowing database operation to be examined in detail. High-level events such as user connections and transactions can be traced as they are processed step-by-step inside the database engine and as the database interacts with the operating system. You can get answers to questions such as the following.

• Which queries are causing random disk I/O?

• What is causing high latency for certain transactions?

• How well do the caches perform for certain queries?

Databases already provide a collection of fixed statistics, often extensive and covering details such as transaction times, byte counts, and cache hit rates. Although these are useful, they are limited to what the database makes ...

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