Anti-Cache Storage

Anti-Cache mode makes RAM a primary storage, while disk becomes a secondary storage.

Sophia implements the mode by introducing so-called index Temperature. The Temperature shows which nodes are the most frequently accessed for read (hot). These nodes are periodically elected and promoted to be put in-memory. Previously elected nodes are unloaded if they do not fit into memory limit.

Following variable can be set to enable anti-cache mode and set the memory limit: db.database_name.storage and memory.anticache.

/* set 1Gb anti-cache limit (for all databases) */
sp_setint(env, "memory.anticache", 1 * 1024 * 1024 * 1024);
/* switch a test database into anti-cache mode */
sp_setstring(env, "db.test.storage", "anti-cache", 0);

The election period is configurable by the following variable: compaction.zone.anticache_period.

/* schedule anti-cache node election every 5 minutes */
sp_setint(env, "compaction.0.anticache_period", 60 * 5);

Database db.database_name.temperature_histogram can be examined to see current temperature distribution among index.

char *temperature = sp_getstring(env, "db.test.temperature_histogram", NULL);
...
free(temperature);

Please take a look at Database and Compaction configuration sections for additional details.

For pure in-memory storage mode see Persistent RAM Storage and Memory-Mapped Storage for semi-in-memory storage mode.