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<h2 class="title" style="clear: both"><a id="db_open"></a>berkdb open</h2>
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<pre class="programlisting">berkdb open
[-auto_commit]
[-btree | -hash | -recno | -queue | -unknown]
[-cachesize {gbytes bytes ncache}]
[-create]
[-delim delim]
[-dup]
[-dupsort]
[-encrypt]
[-encryptaes passwd]
[-encryptany passwd]
[-env env]
[-errfile filename]
[-excl]
[-extent size]
[-ffactor density]
[-len len]
[-mode mode]
[-nelem size]
[-pad pad]
[-pagesize pagesize]
[-rdonly]
[-recnum]
[-renumber]
[-snapshot]
[-source file]
[-truncate]
[-txn txnid]
[--]
[file [database]] </pre>
<p>
The <span class="bold"><strong>berkdb open</strong></span> command opens and
optionally creates a database. The returned database handle is bound
to a Tcl command of the form <span class="bold"><strong>dbN</strong></span>,
where N is an integer starting at 0 (for example, db0 and db1). It is
through this Tcl command that the script accesses the database
methods.
</p>
<p>
The options are as follows:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>-auto_commit</strong></span>
</p>
<p>
Enclose the call within an implicit transaction (you do not need to provide a transaction handle
as a transaction is internally created and commited for you). If the call succeeds, the open
operation will be recoverable and all subsequent database modification
operations based on this handle will be transactionally protected. If
the call fails, no database will have been created.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-btree</strong></span>
</p>
<p>
Open/create a database of type Btree. The Btree format is a
representation of a sorted, balanced tree structure.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-hash</strong></span>
</p>
<p>
Open/create a database of type Hash. The Hash format is an
extensible, dynamic hashing scheme.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-queue</strong></span>
</p>
<p>
Open/create a database of type Queue. The Queue format supports fast
access to fixed-length records accessed by sequentially or logical
record number.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-recno</strong></span>
</p>
<p>
Open/create a database of type Recno. The Recno format supports
fixed- or variable-length records, accessed sequentially or by logical
record number, and optionally retrieved from a flat text file.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-unknown</strong></span>
</p>
<p>
The database is of an unknown type, and must already exist.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-cachesize {gbytes bytes ncache}</strong></span>
</p>
<p>
Set the size of the database's shared memory buffer pool (that is, the
cache), to <span class="bold"><strong>gbytes</strong></span> gigabytes plus
<span class="bold"><strong>bytes</strong></span>. The cache should be the size
of the normal working data set of the application, with some small
amount of additional memory for unusual situations. (Note: The working
set is not the same as the number of simultaneously referenced pages,
and should be quite a bit larger!)
</p>
<p>
The default cache size is 256KB, and may not be specified as less than
20KB. Any cache size less than 500MB is automatically increased by
25% to account for buffer pool overhead; cache sizes larger than 500MB
are used as specified.
</p>
<p>
It is possible to specify caches to Berkeley DB that are large enough
so that they cannot be allocated contiguously on some architectures;
for example, some releases of Solaris limit the amount of memory that
may be allocated contiguously by a process. If <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated
contiguously in memory. If it is greater than 1, the cache will be
broken up into <span class="bold"><strong>ncache</strong></span> equally sized
separate pieces of memory.
</p>
<p>
For information on tuning the Berkeley DB cache size, see
<a href="../../programmer_reference/general_am_conf.html#am_conf_cachesize" class="olink">Selecting a Cache Size</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
<p>
Because databases opened within Berkeley DB environments use the cache
specified to the environment, it is an error to attempt to set a cache
in a database created within an environment.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-create</strong></span>
</p>
<p>
Create any underlying files, as necessary. If the files do not already
exist and the <span class="bold"><strong>-create</strong></span> argument is not
specified, the call will fail.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-delim delim</strong></span>
</p>
<p>
Set the delimiting byte used to mark the end of a record in the
backing source file for the Recno access method.
</p>
<p>
This byte is used for variable length records if the <span class="bold"><strong>-source</strong></span> argument file is specified. If the
<span class="bold"><strong>-source</strong></span> argument file is specified
and no delimiting byte was specified, &lt;newline&gt; characters (that
is, ASCII 0x0a) are interpreted as end-of-record markers.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-dup</strong></span>
</p>
<p>
Permit duplicate data items in the tree, that is, 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 or a duplicate comparison function.
</p>
<p>
It is an error to specify both <span class="bold"><strong>-dup</strong></span> and
<span class="bold"><strong>-recnum</strong></span>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-dupsort</strong></span>
</p>
<p>
Sort duplicates within a set of data items. A default lexical
comparison will be used. Specifying that duplicates are to be sorted
changes the behavior of the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>put</strong></span> operation as well as the
<span class="emphasis"><em>dbc</em></span> <span class="bold"><strong>put</strong></span>
operation when the <span class="bold"><strong>-keyfirst</strong></span>,
<span class="bold"><strong>-keylast</strong></span> and <span class="bold"><strong>-current</strong></span> options are specified.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-encrypt</strong></span>
</p>
<p>
Specify the database in an environment should be encrypted with the
same password that is being used in the environment.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-encryptaes passwd</strong></span>
</p>
<p>
Specify the database should be encrypted with the given password using
the Rijndael/AES (also known as the Advanced Encryption Standard and
Federal Information Processing Standard (FIPS) 197) algorithm.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-encryptany passwd</strong></span>
</p>
<p>
Specify the already existing database should be opened with the given
password. This option is used if the database is known to be
encrypted, but the specific algorithm used is not known.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-env env</strong></span>
</p>
<p>
If no <span class="bold"><strong>-env</strong></span> argument is given, the
database is standalone; that is, it is not part of any Berkeley DB
environment.
</p>
<p>
If a <span class="bold"><strong>-env</strong></span> argument is given, the
database is created within the specified Berkeley DB environment. The
database access methods automatically make calls to the other
subsystems in Berkeley DB, based on the enclosing environment. For
example, if the environment has been configured to use locking, the
access methods will automatically acquire the correct locks when
reading and writing pages of the database.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-errfile filename</strong></span>
</p>
<p>
When an error occurs in the Berkeley DB library, a Berkeley DB error
or an error return value is returned by the function. In some cases,
however, the errno value may be insufficient to completely describe
the cause of the error especially during initial application
debugging.
</p>
<p>
The <span class="bold"><strong>-errfile</strong></span> argument is used to
enhance the mechanism for reporting error messages to the application
by specifying a file to be used for displaying additional Berkeley DB
error messages. In some cases, when an error occurs, Berkeley DB will
output an additional error message to the specified file reference.
</p>
<p>
The error message will consist of a Tcl command name and a colon
(":"), an error string, and a trailing &lt;newline&gt; character. If
the database was opened in an environment, the Tcl command name will
be the environment name (for example, env0), otherwise it will be the
database command name (for example, db0).
</p>
<p>
This error-logging enhancement does not slow performance or
significantly increase application size, and may be run during normal
operation as well as during application debugging.
</p>
<p>
For database handles opened inside of Berkeley DB environments,
specifying the <span class="bold"><strong>-errfile</strong></span> argument
affects the entire environment and is equivalent to specifying the
same argument to the <span class="bold"><strong>berkdb env</strong></span>
command.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-excl</strong></span>
</p>
<p>
Return an error if the database already exists.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-extent size</strong></span>
</p>
<p>
Set the size of the extents of the Queue database; the size is
specified as the number of pages in an extent. Each extent is created
as a separate physical file. If no extent size is set, the default
behavior is to create only a single underlying database file.
</p>
<p>
For information on tuning the extent size, see
<a href="../../programmer_reference/rq_conf.html#am_conf_extentsize" class="olink">Selecting an Extent Size</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-ffactor density</strong></span>
</p>
<p>
Set the desired density within the hash table.
</p>
<p>
The density is an approximation of the number of keys allowed to
accumulate in any one bucket
</p>
</li>
<li>
<p>
<span class="bold"><strong>-len len</strong></span>
</p>
<p>
For the Queue access method, specify that the records are of length
<span class="bold"><strong>len</strong></span>.
</p>
<p>
For the Recno access method, specify that the records are
fixed-length, not byte-delimited, and are of length <span class="bold"><strong>len</strong></span>.
</p>
<p>
Any records added to the database that are less than <span class="bold"><strong>len</strong></span> bytes long are automatically padded (see
the <span class="bold"><strong>-pad</strong></span> argument for more
information).
</p>
<p>
Any attempt to insert records into the database that are greater than
<span class="bold"><strong>len</strong></span> bytes long will cause the call to
fail immediately and return an error.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-mode mode</strong></span>
</p>
<p>
On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all
files created by the access methods are created with mode <span class="bold"><strong>mode</strong></span> (as described in <span class="bold"><strong>chmod</strong></span>(2)) and modified by the process' umask
value at the time of creation (see <span class="bold"><strong>umask</strong></span>(2)). The group ownership of created
files is based on the system and directory defaults, and is not
further specified by Berkeley DB. If <span class="bold"><strong>mode</strong></span> is 0, files are created readable and
writable by both owner and group. On Windows systems, the mode
argument is ignored.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-nelem size</strong></span>
</p>
<p>
Set an estimate of the final size of the hash table.
</p>
<p>
If not set or set too low, hash tables will still expand gracefully as
keys are entered, although a slight performance degradation may be
noticed.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-pad pad</strong></span>
</p>
<p>
Set the padding character for short, fixed-length records for the
Queue and Recno access methods.
</p>
<p>
If no pad character is specified, &lt;space&gt; characters (that is,
ASCII 0x20) are used for padding.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-pagesize pagesize</strong></span>
</p>
<p>
Set the size of the pages used to hold items in the database, in
bytes. The minimum page size is 512 bytes, and the maximum page size
is 64K bytes. If the page size is not explicitly set, one is selected
based on the underlying filesystem I/O block size. The automatically
selected size has a lower limit of 512 bytes and an upper limit of 16K
bytes.
</p>
<p>
For information on tuning the Berkeley DB page size, see
<a href="../../programmer_reference/general_am_conf.html#am_conf_pagesize" class="olink">Selecting a Page Size</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-rdonly</strong></span>
</p>
<p>
Open the database for reading only. Any attempt to modify items in the
database will fail, regardless of the actual permissions of any
underlying files.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-recnum</strong></span>
</p>
<p>
Support retrieval from the Btree using record numbers.
</p>
<p>
Logical record numbers in Btree databases are mutable in the face of
record insertion or deletion. See the <span class="bold"><strong>-renumber</strong></span> argument for further discussion.
</p>
<p>
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 <span class="bold"><strong>-recnum</strong></span>
can result in serious performance degradation for some applications
and data sets.
</p>
<p>
It is an error to specify both <span class="bold"><strong>-dup</strong></span>
and <span class="bold"><strong>-recnum</strong></span>.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-renumber</strong></span>
</p>
<p>
Specifying the <span class="bold"><strong>-renumber</strong></span> argument
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 one. If a cursor was positioned to record
number 4 before the deletion, it will refer to 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 one logical record, continuing to refer to the same
record as it did before.
</p>
<p>
Using the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>put</strong></span>
or <span class="emphasis"><em>dbc</em></span> <span class="bold"><strong>put</strong></span>
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.
</p>
<p>
If a created record is not at the end of the database, all records
following the new record will be automatically renumbered upward by
one. For example, the creation of a new record numbered 8 causes
records numbered 8 and greater to be renumbered upward by one. If a
cursor was positioned to record number 8 or greater before the
insertion, it will be shifted upward one logical record, continuing to
refer to the same record as it did before.
</p>
<p>
For these reasons, concurrent access to a Recno database with the
<span class="bold"><strong>-renumber</strong></span> flag specified may be
largely meaningless, although it is supported.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-snapshot</strong></span>
</p>
<p>
This argument specifies that any specified <span class="bold"><strong>-source</strong></span> file be read in its entirety when the
database is opened. If this argument is not specified, the <span class="bold"><strong>-source</strong></span> file may be read lazily.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-source file</strong></span>
</p>
<p>
Set the underlying source file for the Recno access method. The
purpose of the <span class="bold"><strong>-source</strong></span> file is to
provide fast access and modification to databases that are normally
stored as flat text files.
</p>
<p>
If the <span class="bold"><strong>-source</strong></span> argument is give, 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 <span class="bold"><strong>-delim</strong></span>. For example, standard UNIX byte stream
files can be interpreted as a sequence of variable length records
separated by &lt;newline&gt; characters.
</p>
<p>
In addition, when cached data would normally be written back to the
underlying database file (for example, when the
<span class="emphasis"><em>db</em></span> <span class="bold"><strong>close</strong></span> or
<span class="emphasis"><em>db</em></span> <span class="bold"><strong>sync</strong></span> commands
are called), the in-memory copy of the database will be written back
to the <span class="bold"><strong>-source</strong></span> file.
</p>
<p>
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. <span class="bold"><strong>If multiple processes (not threads)
are accessing a Recno database concurrently and 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 argument as part of the
<span class="bold"><strong>berkdb open</strong></span> call. See the <span class="bold"><strong>-snapshot</strong></span> argument for more
information.</strong></span>
</p>
<p>
<span class="bold"><strong>Reading and writing the backing source file
specified by <span class="bold"><strong>-source</strong></span> cannot be
transaction protected because it involves filesystem operations that
are not part of the Berkeley DB transaction methodology.</strong></span>
For this reason, if a temporary database is used to hold the records,
it is possible to lose the contents of the <span class="bold"><strong>-source</strong></span> file, for example, if the system crashes
at the right instant. If a file is used to hold the database, that
is, a filename was specified as the <span class="bold"><strong>file</strong></span> argument to <span class="bold"><strong>berkdb
open</strong></span>, normal database recovery on that file can be used to
prevent information loss, although it is still possible that the
contents of <span class="bold"><strong>-source</strong></span> file will be lost if
the system crashes.
</p>
<p>
The <span class="bold"><strong>-source</strong></span> file must already exist
(but may be zero-length) when <span class="bold"><strong>berkdb
open</strong></span> is called.
</p>
<p>
It is not an error to specify a read-only <span class="bold"><strong>-source</strong></span> 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
<span class="emphasis"><em>db</em></span> <span class="bold"><strong>close</strong></span> or
<span class="emphasis"><em>db</em></span> <span class="bold"><strong>sync</strong></span> commands
will fail, of course. Specifying the <span class="bold"><strong>-nosync</strong></span> argument to the <span class="emphasis"><em>db</em></span>
<span class="bold"><strong>close</strong></span> command will stop it from
attempting to write the changes to the backing file; instead, they
will be silently discarded.
</p>
<p>
For all of the previous reasons, the <span class="bold"><strong>-source</strong></span> file 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 such as a text editor.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-truncate</strong></span>
</p>
<p>
Physically truncate the underlying file, discarding all previous
databases it might have held. Underlying filesystem primitives are
used to implement this flag. For this reason, it is only applicable
to the physical file and cannot be used to discard databases within a
file.
</p>
<p>
The <span class="bold"><strong>-truncate</strong></span> argument cannot be
transaction-protected, and it is an error to specify it in a
transaction-protected environment.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-txn txnid</strong></span>
</p>
<p>
If the operation is part of an application-specified transaction, the
<span class="bold"><strong>txnid</strong></span> parameter is a transaction
handle returned from <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span>. If no transaction handle is specified,
but the -auto_commit flag is specified, the operation will be
implicitly transaction protected.
</p>
</li>
<li>
<p>
<span class="bold"><strong>--</strong></span>
</p>
<p>
Mark the end of the command arguments.
</p>
</li>
<li>
<p>
<span class="bold"><strong>file</strong></span>
</p>
<p>
The name of a single physical file on disk that will be used to back
the database.
</p>
<p>
An in-memory database never intended to be preserved on
disk may be created by not specifying a file name. For
example:
</p>
<pre class="programlisting">berkdb open -create -btree </pre>
<p>
creates an in-memory database.
</p>
</li>
<li>
<p>
<span class="bold"><strong>database</strong></span>
</p>
<p>
The <span class="bold"><strong>database</strong></span> argument allows
applications to have multiple databases inside of a single physical
file. This is useful when the databases are both numerous and
reasonably small, in order to avoid creating a large number of
underlying files. It is an error to attempt to open a second database
file that was not initially created using a <span class="bold"><strong>database</strong></span> name.
</p>
<p>
Applications opening multiple databases in a single file will almost
certainly need to create a shared database environment. See
<a href="../../programmer_reference/am_opensub.html" class="olink">Opening multiple databases in a single file</a>
in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more
information.
</p>
<p>
If more than one in-memory database is desired, it is
necessary to specify an empty string as the database name.
For example:
</p>
<pre class="programlisting">berkdb open -create -btree "" foo
berkdb open -create -btree "" bar </pre>
<p>
will create two databases, neither of which will appear on
disk.
</p>
</li>
</ul>
</div>
<p>
The <span class="bold"><strong>berkdb open</strong></span> command returns a
database handle on success.
</p>
<p>
In the case of error, a Tcl error is thrown.
</p>
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<td width="40%" align="left" valign="top"><span class="emphasis"><em>db</em></span> join </td>
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<td width="40%" align="right" valign="top"> <span class="emphasis"><em>db</em></span> put</td>
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