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The "ArchitectureCommitLog" page has been changed by JonathanEllis. The comment on this change is: add ! to CL terms and start using CLSegment term. http://wiki.apache.org/cassandra/ArchitectureCommitLog?action=diff&rev1=2&rev2=3 -------------------------------------------------- - Each CommitLog has a CommitLogHeader. A CommitLogHeader has one entry per ColumnFamily. Each entry has a dirty bit and a replay offset, indicating the position in the CommitLog file to start replaying the log for a particular ColumnFamily. + Each !CommitLog has a !CommitLogHeader. A !CommitLogHeader has one entry per !ColumnFamily. Each entry has a dirty bit and a replay offset, indicating the position in the !CommitLog file to start replaying the log for a particular !ColumnFamily. - Each insertion (deletion) has to first write a log entry to the CommitLog. + Each insertion (deletion) has to first write a log entry to the !CommitLog. - * The writing of all log entries is handled by a single thread in CommitLogExecutorService. + * The writing of all log entries is handled by a single thread in !CommitLogExecutorService. - * For each insert, the CommitLogHeader is first updated, if necessary. + * For each insert, the !CommitLogHeader is first updated, if necessary. - * For each ColumnFamily CF to be inserted, if the dirty bit for CF in the CommitLogHeader is off, the dirty bit is turned on and the replay offset for CF in the CommitLogHeader is updated with the current position in the CommitLog file. + * For each !ColumnFamily CF to be inserted, if the dirty bit for CF in the !CommitLogHeader is off, the dirty bit is turned on and the replay offset for CF in the !CommitLogHeader is updated with the current position in the CommitLog file. - * A log entry is then added to the tail of the CommitLog file. + * A log entry is then added to the tail of the !CommitLog file. - * If CommitLogSync is set to batch, the insertion further waits until the CommitLog file is sync-ed to disk before the client is acknowledged. + * If !CommitLogSync is set to batch, the insertion further waits until the !CommitLog file is sync-ed to disk before the insert is allowed to proceed - * Once a CommitLog file becomes too large, a new CommitLog file is rolled in. + * Once a !CommitLog file (!CommitLogSegment) becomes too large, a new segment is created and new operations are appended there instead. - On the completion of a flush for a ColumnFamily CF, + On the completion of a flush for a !ColumnFamily, - * For each CommitLog file F generated when or before the flush is initiated, + * For each !CommitLogSegment F generated when or before the flush is initiated, - * If F is not the one being used when the flush was initated, the dirty bit for CF in the CommitLogHeader of F is turned off + * If F is not the one being used when the flush was initated, the dirty bit for CF in the !CommitLogHeader of F is turned off - * If all dirty bits in the CommitLogHeader are off, F is deleted. + * If all dirty bits in the !CommitLogHeader are off, F is deleted. - * Otherwise, the dirty bit for CF in the CommitLogHeader is turned on and the replay offset for CF is updated with the position in the log file when the flush was initiated. + * Otherwise, the dirty bit for CF in the !CommitLogHeader is turned on and the replay offset for CF is updated with the position in the log file when the flush was initiated. Recovery during a restart, - * Each CommitLog file is iterated in ascending time order. + * Each !CommitLogSegment is iterated in ascending time order. - * The CommitLog file is read from the lowest replay offset among all entries in the CommitLogHeader. + * The segment is read from the lowest replay offset among all entries in the !CommitLogHeader. - * For each log entry read, the log is replayed for a ColumnFamily CF if the position of the log entry is no less than the replay offset for CF in the CommitLogHeader. + * For each log entry read, the log is replayed for a !ColumnFamily CF if the position of the log entry is no less than the replay offset for CF in the !CommitLogHeader. - * When log replay is done, all MemTables are force flushed to disk and all CommitLog files are deleted. + * When log replay is done, all Memtables are force flushed to disk and all commitlog segments are deleted.
