Low-level write cache service.

See: Description

Package Description

Low-level write cache service. Application writes are absorbed on records destined for some byte offset on the backing persistent store. Those records are transferred into a write cache rather than writing them directly onto the backing file. The write cache service provides an abstraction supporting one or more write cache blocks so the application can write ahead of the disk. The write cache itself consists of a record map, which specifies where each record will be written onto the backing file, and a large direct ByteBuffer, which contains the raw data to be written onto the file. For the RW store, those records will be scattered. For the WORM, they will be appended (and the record map is ignored). The write cache coordinates with the journal to provide per- record checksums.

The write cache is also the basis for replicated writes in support of high availability. The entire write cache is check summed and transfered using NIO to each service in a highly available quorum.

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