Db.set_flags
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import com.sleepycat.db.*;
public void set_flags(int flags)
throws DbException;
Description
Calling Db.set_flags is additive, there is no way to clear flags.
The flags value must be set to 0 or by bitwise inclusively OR'ing together one or more
of the following values.
Btree
The following flags may be specified for the Btree access method:
- Db.DB_DUP
- Permit duplicate data items in the tree, i.e. insertion when the key of
the key/data pair being inserted already exists in the tree will be
successful. The ordering of duplicates in the tree is determined by the
order of insertion, unless the ordering is otherwise specified by use of
a cursor operation. It is an error to specify both Db.DB_DUP and
Db.DB_RECNUM.
- Db.DB_DUPSORT
- Permit duplicate data items in the tree, i.e. insertion when the key of
the key/data pair being inserted already exists in the tree will be
successful. The ordering of duplicates in the tree is determined by the
duplicate comparison function.
A default, lexical comparison will be used.
It is an error to specify both Db.DB_DUPSORT and Db.DB_RECNUM.
- Db.DB_RECNUM
- Support retrieval from the Btree using record numbers. For more
information, see the DB_GET_RECNO flag to the Db.get and
Dbc.get methods.
Logical record numbers in Btree databases are mutable in the face of
record insertion or deletion. See the DB_RENUMBER flag in the Recno
access method information for further discussion.
Maintaining record counts within a Btree introduces a serious point of
contention, namely the page locations where the record counts are stored.
In addition, the entire tree must be locked during both insertions and
deletions, effectively single-threading the tree for those operations.
Specifying DB_RECNUM can result in serious performance degradation for
some applications and data sets.
It is an error to specify both DB_DUP and DB_RECNUM.
- Db.DB_REVSPLITOFF
- Turn off reverse splitting in the Btree. As pages are emptied in a
database, the Berkeley DB Btree implementation attempts to coalesce empty pages
into higher-level pages in order to keep the tree as small as possible
and minimize tree search time. This can hurt performance in applications
with cyclical data demands, that is, applications where the database grows
and shrinks repeatedly. For example, because Berkeley DB does page-level
locking, the maximum level of concurrency in a database of 2 pages is far
smaller than that in a database of 100 pages, and so a database that has
shrunk to a minimal size can cause severe deadlocking when a new cycle of
data insertion begins.
Hash
The following flags may be specified for the Hash access method:
- Db.DB_DUP
- Permit duplicate data items in the tree, i.e. insertion when the key of
the key/data pair being inserted already exists in the tree will be
successful. The ordering of duplicates in the tree is determined by the
order of insertion, unless the ordering is otherwise specified by use of
a cursor operation. It is an error to specify both Db.DB_DUP and
Db.DB_RECNUM.
- Db.DB_DUPSORT
- Permit duplicate data items in the tree, i.e. insertion when the key of
the key/data pair being inserted already exists in the tree will be
successful. The ordering of duplicates in the tree is determined by the
duplicate comparison function.
A default, lexical comparison will be used.
It is an error to specify both Db.DB_DUPSORT and Db.DB_RECNUM.
Queue
There are no additional flags that may be specified for the Queue access
method.
Recno
The following flags may be specified for the Recno access method:
- Db.DB_RENUMBER
- Specifying the DB_RENUMBER flag causes the logical record numbers to be
mutable, and change as records are added to and deleted from the database.
For example, the deletion of record number 4 causes records numbered 5
and greater to be renumbered downward by 1. If a cursor was positioned
to record number 4 before the deletion, it will reference the new record
number 4, if any such record exists, after the deletion. If a cursor was
positioned after record number 4 before the deletion, it will be shifted
downward 1 logical record, continuing to reference the same record as it
did before.
Using the Db.put or Dbc.put interfaces to create new
records will cause the creation of multiple records if the record number
is more than one greater than the largest record currently in the
database. For example, creating record 28, when record 25 was previously
the last record in the database, will create records 26 and 27 as well as
28. Attempts to retrieve records that were created in this manner will
result in an error return of Db.DB_KEYEMPTY.
If a created record is not at the end of the database, all records
following the new record will be automatically renumbered upward by 1.
For example, the creation of a new record numbered 8 causes records
numbered 8 and greater to be renumbered upward by 1. If a cursor was
positioned to record number 8 or greater before the insertion, it will be
shifted upward 1 logical record, continuing to reference the same record
as it did before.
For these reasons, concurrent access to a Recno database with the
Db.DB_RENUMBER flag specified may be largely meaningless, although
it is supported.
- Db.DB_SNAPSHOT
- This flag specifies that any specified re_source file be read in
its entirety when Db.open is called. If this flag is not
specified, the re_source file may be read lazily.
The Db.set_flags interface may only be used to configure Berkeley DB before
the Db.open interface is called.
The Db.set_flags method throws an exception that encapsulates a non-zero error value on
failure.
Errors
- EINVAL
- An invalid flag value or parameter was specified.
Class
Db
See Also
Db.close,
Db.cursor,
Db.del,
Db.fd,
Db.get,
Db.get_byteswapped,
Db.get_type,
Db.join,
Db.key_range,
Db.open,
Db.put,
Db.remove,
Db.set_bt_minkey,
Db.set_cachesize,
Db.set_errcall,
Db.set_errpfx,
Db.set_flags,
Db.set_h_ffactor,
Db.set_h_nelem,
Db.set_lorder,
Db.set_pagesize,
Db.set_re_delim,
Db.set_re_len,
Db.set_re_pad,
Db.set_re_source,
Db.stat,
Db.sync,
Db.upgrade
and
Db.verify.
Copyright Sleepycat Software