Db::close
Db::close |
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#include <db_cxx.h>int Db::close(u_int32_t flags);
The Db::close method flushes any cached database information to disk, closes any open cursors, frees any allocated resources, and closes any underlying files. Since key/data pairs are cached in memory, failing to sync the file with the Db::close or Db::sync method may result in inconsistent or lost information.
The flags parameter must be set to 0 or the following value:
The DB_NOSYNC flag is a dangerous option. It should only be set if the application is doing logging (with transactions) so that the database is recoverable after a system or application crash, or if the database is always generated from scratch after any system or application crash.
It is important to understand that flushing cached information to disk only minimizes the window of opportunity for corrupted data. While unlikely, it is possible for database corruption to happen if a system or application crash occurs while writing data to the database. To ensure that database corruption never occurs, applications must either: use transactions and logging with automatic recovery, use logging and application-specific recovery, or edit a copy of the database, and, once all applications using the database have successfully called Db::close, atomically replace the original database with the updated copy.
When multiple threads are using the Berkeley DB handle concurrently, only a single thread may call the Db::close method.
Once Db::close has been called, regardless of its return, the Db handle may not be accessed again.
The Db::close method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, 0 on success, and returns DB_INCOMPLETE if the underlying database still has dirty pages in the cache. (The only reason to return DB_INCOMPLETE is if another thread of control was writing pages in the underlying database file at the same time as the Db::close method was called. For this reason, a return of DB_INCOMPLETE can normally be ignored, or, in cases where it is a possible return value, the DB_NOSYNC option should probably have been specified.)
The Db::close method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.
The Db::close method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the Db::close method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.
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