Set the underlying source file for the Recno access method. The purpose
of the re_source value is to provide fast access and modification
to databases that are normally stored as flat text files.
If the re_source field is set, it specifies an underlying flat
text database file that is read to initialize a transient record number
index. In the case of variable length records, the records are
separated, as specified by Db::set_re_delim. For example,
standard UNIX byte stream files can be interpreted as a sequence of
variable length records separated by <newline> characters.
In addition, when cached data would normally be written back to the
underlying database file (for example, the Db::close or
Db::sync methods are called), the in-memory copy of the database
will be written back to the re_source file.
By default, the backing source file is read lazily; that is, records
are not read from the file until they are requested by the application.
If multiple processes (not threads) are accessing a Recno database
concurrently, and are either inserting or deleting records, the backing
source file must be read in its entirety before more than a single
process accesses the database, and only that process should specify the
backing source file as part of the Db::open call. See the
DB_SNAPSHOT flag for more information.
Reading and writing the backing source file specified by re_source
cannot be transaction-protected because it involves filesystem
operations that are not part of the Db transaction methodology. For
this reason, if a temporary database is used to hold the records, it is
possible to lose the contents of the re_source file, for
example, if the system crashes at the right instant. If a file is used
to hold the database, normal database recovery on that file can be used
to prevent information loss, although it is still possible that the
contents of re_source will be lost if the system crashes.
The re_source file must already exist (but may be zero-length) when
Db::open is called.
It is not an error to specify a read-only re_source file when
creating a database, nor is it an error to modify the resulting database.
However, any attempt to write the changes to the backing source file using
either the Db::sync or Db::close methods will fail, of course.
Specify the DB_NOSYNC flag to the Db::close method to stop it
from attempting to write the changes to the backing file; instead, they
will be silently discarded.
For all of the previous reasons, the re_source field is generally
used to specify databases that are read-only for Berkeley DB applications;
and that are either generated on the fly by software tools or modified
using a different mechanism -- for example, a text editor.
The Db::set_re_source method configures operations performed using the specified
Db handle, not all operations performed on the underlying
The Db::set_re_source interface may not be called after the Db::open
interface is called.
If the database already exists when
Db::open is called, the information specified to Db::set_re_source must
be the same as that historically used to create the database or
corruption can occur.
The Db::set_re_source 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::set_re_source method may fail and throw an exception or return a non-zero error for the following conditions:
- An invalid flag value or parameter was specified.
Called after Db::open was called.
The Db::set_re_source 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::set_re_source method may fail and
either return DB_RUNRECOVERY or throw a
in which case all subsequent Berkeley DB calls will fail in the same way.
Databases and Related Methods
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