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Programming Distributed Systems with YAMI4

7.3.4 Startup and Configuration

The YAMI4 cache server is a separate, natively compiled program, that can be run from its directory with a simple invocation:

$ ./yami4cache

The server accepts optionally a name of configuration file as a parameter, but if none is given then the yami4cache.cfg file is used by default.

The configuration file is a text file and defines the following properties:

• listener - the listener target for the name server,
• data.max-total-size - the maximum size of all data values stored together,
• data.eviction_time - the expiration time for any given value in seconds,
• data.eviction_scan_period - the time, in seconds, between subsequent scans of the data storage - if this time is set to zero, the periodic scan is not performed, and effectively data entries will never expire,
• log.main, log.evictor, log.messages - flags enabling the particular logging subsystems.

The cache server reports its activity on standard output, according to logging flags defined in the configuration file.

The internally managed memory storage is automatically managed in two ways:

• Removal of expired entries - all entries that are older than the configured eviction time are automatically removed; the time is not supposed to be measured precisely, and it is subject to delays related to the data scan period.
• Limit on the total size of stored data - the configured limit is not supposed to be exact and only takes into account the sizes of data buffers for the ``value'' part of each entry, the keys are not counted.

Even though the above mechanisms do not offer any precise timing or size accounting, they can provide an effective ``first line of defense'' against excessive memory usage.