Log Cache — log information is kept in memory and flushed to the Falcon Log when transactions commit. Falcon keeps eight 1 MB windows into the log file for reading and writing.

System and Index Cache — data needed by Falcon (table and field definitions, transaction state, etc.) is also maintained in memory for quick reference. In addition, local index accelerators represent index segments created by a running transaction are also stored in the system memory. When a transaction changes indexed fields, it builds an index accelerator section in system memory, representing its changes. On commit, all index changes for the transaction are written to the serial log in sorted order and later merged with the permanent index by the worker thread.

Page Cache — database pages read from disk for a particular database. The page cache size is controlled by the falcon_page_cache_size parameter, which defaults to 4MB, and is set in the my.cnf file. Although record and index changes go to the serial log before being written to database pages, blob data is written directly into the page cache. This avoids logging large data items that are rarely referenced or changed by the transaction that creates them.

Record Cache — the record cache is a memory region devoted to holding rows that have been requested by end-user queries for a particular database or created by active transactions. Note that this cache differs from traditional data caches in that only specific rows needed by applications reside in the cache as opposed to entire data pages (which may contain only subsets of needed information). The record cache can hold several versions of records that have been modified or deleted. This technique guarantees that active data needed to satisfy user requests is in memory, shortens row access time, and reduces cache bloat by not including unrequested information. The record cache also assists in supporting the multi-version concurrency control (MVCC) mechanisms of the Falcon engine. The record cache is controlled by two parameters. The falcon_min_record_memory parameter (default 10MB) determines the minimum amount of RAM supplied to the record cache and the falcon_max_record_memory (default 20MB) limits the total amount of memory available to the cache.

Because of the support the record cache supplies to transactions, a scavenge thread is used to ensure only “hot” data resides in the cache. When the falcon_max_record_memory limit is reached, Falcon surveys the demographics of the generational data in the cache, and removes the oldest generations. This process is more complicated than the standard LRU algorithm used by many database systems, but it is more efficient and faster.