When it comes to performance, BerkeleyDB’s cache size is the single most important configuration parameter. In order to achieve maximum performance, the data most frequently accessed by your application should be cached so that read and write requests do not trigger too much I/O activity.
BerkeleyDB databases are grouped together in application environments - directories which group data and log files along with common settings used by a particular application. The database cache is global for all databases in a particular environment and needs to be allocated at the time that environment is created. Most of the time this is done programmaticaly. The issue of course is that, the optimal cache size is directly related to the size of the data set, which is not always known at application design time. Many BerkeleyDB applications end up storing considerably more data than originally envisioned. Even worse, some applications do not explicitly specify a cache size at all, so the default cache size of 256KB is allocated – which far too low for many applications. Such applications suffer from degraded performance as they accumulate more data; their performance can be significantly improved by increasing the cache size. Luckily, most of the time this can be achieved without any code changes by creating a configuration file in your BerkeleyDB application environment. Read more…
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