The Logging subsystem is the logging facility used by Berkeley DB. It is largely Berkeley DB-specific, although it is potentially useful outside of the Berkeley DB package for applications wanting write-ahead logging support. Applications wanting to use the log for purposes other than logging file modifications based on a set of open file descriptors will almost certainly need to make source code modifications to the Berkeley DB code base.
A log can be shared by any number of threads of control. The DB_ENV->open interface is used to open a log. When the log is no longer in use, it should be closed using the DB_ENV->close interface.
Individual log entries are identified by log sequence numbers. Log sequence numbers are stored in an opaque object, a DB_LSN.
The log_put interface is used to append new log records to the log. Optionally, the DB_CHECKPOINT flag can be used to output a checkpoint log record (indicating that the log is consistent to that point, and recoverable after a system or application failure), as well as open-file information. The log_get interface is used to retrieve log records from the log.
There are additional interfaces for integrating the log subsystem with a transaction processing system:
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