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Berkeley DB 3.x & 4.x Python Extension Package
Introduction
This is a simple bit of documentation for the bsddb3.db Python
extension module which wraps the Berkeley DB 3.x or 4.x C library.
The extension module is located in a Python package along with a few
pure python modules.
It is expected that this module will be used in the following
general ways by different programmers in different situations.
The goals of this module are to allow all of these methods without
making things too complex for the simple cases, and without
leaving out funtionality needed by the complex cases.
1. **Backwards compatibility** -- It is desirable for this package
to be a near drop-in replacement for the bsddb module shipped
with Python which is designed to wrap either DB 1.85, or the
1.85 compatibility interface. This means that there will need
to be equivalent object creation functions available,
(btopen(), hashopen(), and rnopen()) and the objects returned
will need to have the same or at least similar methods
available, (specifically, first(), last(), next(), and prev()
will need to be available without the user needing to
explicitly use a cursor.) All of these have been implemented
in Python code in the bsddb3.__init__.py module.
2. **Simple persistent dictionary** -- One small step beyond the
above. The programmer may be aware of and use the new DB
object type directly, but only needs it from a single process
and thread. The programmer should not have to be bothered
with using a DBEnv, and the DB object should behave as much
like a dictionary as possible.
3. **Concurrent access dictionaries** -- This refers to the
ability to simultaneously have one writer and multiple
readers of a DB (either in multiple threads or processes) and
is implemented simply by creating a DBEnv with certain flags.
No extra work is required to allow this access mode in
bsddb3.
4. **Advanced transactional data store** -- This mode of use is
where the full capabilities of the Berkeley DB library are
called into action. The programmer will probably not use the
dictionary access methods as much as the regular methods of
the DB object, so he can pass transaction objects to the
methods. Again, most of this advanced functionality is
activated simply by opening a DBEnv with the proper flags,
and also by using transactions and being aware of and
reacting to deadlock exceptions, etc.
Types Provided
The bsddb3.db extension module provides the following object types:
- **DB**: The basic database object, capable of Hash, BTree,
Recno, and Queue access methods.
- **DBEnv**: Provides a Database Environment for more advanced
database use. Apps using transactions, logging,
concurrent access, etc. will need to have an
environment object.
- **DBCursor**: A pointer-like object used to traverse a
database.
- **DBTxn**: A database transaction. Allows for multi-file
commit, abort and checkpoint of database
modifications.
- **DBLock**: An opaque handle for a lock. See DBEnv.lock_get()
and DBEnv.lock_put(). Locks are not necessarily
associated with anything in the database, but can
be used for any syncronization task across all
threads and processes that have the DBEnv open.
Exceptions Provided
The BerkeleyDB C API uses function return codes to signal various
errors. The bsddb3.db module checks for these error codes and
turns them into Python exceptions, allowing you to use familiar
try:... except:... constructs and not have to bother with checking
every method's return value.
Each of the error codes is turned into an exception specific to
that error code, as outlined in the table below. If you are using
the C API documentation then it is very easy to map the error
return codes specified there to the name of the Python exception
that will be raised. Simply refer to the table below.
Each exception derives from the DBError exception class so if you
just want to catch generic errors you can use DBError to do it.
Since DBNotFoundError is raised when a given key is not found in
the database, DBNotFoundError also derives from the standard
KeyError exception to help make a DB look and act like a
dictionary.
When any of these exceptions is raised, the associated value is a
tuple containing an integer representing the error code and a
string for the error message itself.
|-----------------------------------------------------------------------|
| **DBError** | Base class, all others derive from this |
|-----------------------------------------------------------------------|
| **DBIncompleteError** | DB_INCOMPLETE |
|-----------------------------------------------------------------------|
| **DBKeyEmptyError** | DB_KEYEMPTY |
|-----------------------------------------------------------------------|
| **DBKeyExistError** | DB_KEYEXIST |
|-----------------------------------------------------------------------|
| **DBLockDeadlockError** | DB_LOCK_DEADLOCK |
|-----------------------------------------------------------------------|
| **DBLockNotGrantedError** | DB_LOCK_NOTGRANTED |
|-----------------------------------------------------------------------|
| **DBNotFoundError** | DB_NOTFOUND (also derives from KeyError) |
|-----------------------------------------------------------------------|
| **DBOldVersionError** | DB_OLD_VERSION |
|-----------------------------------------------------------------------|
| **DBRunRecoveryError** | DB_RUNRECOVERY |
|-----------------------------------------------------------------------|
| **DBVerifyBadError** | DB_VERIFY_BAD |
|-----------------------------------------------------------------------|
| **DBNoServerError** | DB_NOSERVER |
|-----------------------------------------------------------------------|
| **DBNoServerHomeError** | DB_NOSERVER_HOME |
|-----------------------------------------------------------------------|
| **DBNoServerIDError** | DB_NOSERVER_ID |
|-----------------------------------------------------------------------|
| **DBInvalidArgError** | EINVAL |
|-----------------------------------------------------------------------|
| **DBAccessError** | EACCES |
|-----------------------------------------------------------------------|
| **DBNoSpaceError** | ENOSPC |
|-----------------------------------------------------------------------|
| **DBNoMemoryError** | ENOMEM |
|-----------------------------------------------------------------------|
| **DBAgainError** | EAGAIN |
|-----------------------------------------------------------------------|
| **DBBusyError** | EBUSY |
|-----------------------------------------------------------------------|
| **DBFileExistsError** | EEXIST |
|-----------------------------------------------------------------------|
| **DBNoSuchFileError** | ENOENT |
|-----------------------------------------------------------------------|
| **DBPermissionsError** | EPERM |
|-----------------------------------------------------------------------|
Other Package Modules
- **dbshelve.py**: This is an implementation of the standard
Python shelve concept for storing objects that uses bsddb3
specifically, and also exposes some of the more advanced
methods and capabilities of the underlying DB.
- **dbtables.py**: This is a module by Gregory Smith that
implements a simplistic table structure on top of a DB.
- **dbutils.py**: A catch-all for python code that is generally
useful when working with DB's
- **dbobj.py**: Contains subclassable versions of DB and DBEnv.
- **dbrecio.py**: Contains the DBRecIO class that can be used to
do partial reads and writes from a DB record using a
file-like interface. Contributed by Itamar Shtull-Trauring.
Testing
A full unit test suite is being developed to exercise the various
object types, their methods and the various usage modes described
in the introduction. "PyUnit":http://pyunit.sourceforge.net/ is
used and the tests are structured such that they can be run
unattended and automated. There are currently over 150 test cases!
Reference
See the C language API "online
documentation":http://www.oracle.com/technology/documentation/berkeley-db/db/index.html on
Oracle's website (or the "local copy":api_c/c_index.html ) for more
details of the functionality of each of these methods. The names
of all the Python methods should be the same or similar to the
names in the C API.
This version of the documentation was originally based on Berkeley
DB 3.3. If you build the module with a different version of
Berkeley DB then the items below and in the Oracle Berkeley DB docs may not
be entirely accurate. Refer to the "Oracle Berkeley DB
documentation":http://www.oracle.com/technology/documentation/berkeley-db/db/index.html for true details.
**NOTE:** All the methods shown below having more than one keyword
argument are actually implemented using keyword argument parsing,
so you can use keywords to provide optional parameters as
desired. Those that have only a single optional argument are
implemented without keyword parsing to help keep the
implementation simple. If this is too confusing let me know and
I'll think about using keywords for everything.
DBEnv Attributes
db_home --
database home directory (read-only)
DBEnv Methods
DBEnv(flags=0): --
Constructor
"More info...":api_c/env_create.html
close(flags=0): --
Close the database environment, freeing resources.
"More info...":api_c/env_close.html
open(homedir, flags=0, mode=0660): --
Prepare the database environment for use.
"More info...":api_c/env_open.html
remove(homedir, flags=0): --
Remove a database environment.
"More info...":api_c/env_remove.html
set_cachesize(gbytes, bytes, ncache=0): --
Set the size of the shared memory buffer pool
"More info...":api_c/env_set_cachesize.html
set_data_dir(dir): --
Set the environment data directory
"More info...":api_c/env_set_data_dir.html
set_flags(flags, onoff): --
Set additional flags for the DBEnv. The onoff
parameter specifes if the flag is set or cleared.
"More info...":api_c/env_set_flags.html
set_tmp_dir(dir): --
Set the directory to be used for temporary files
"More info...":api_c/env_set_tmp_dir.html
set_get_returns_none(flag): --
By default when DB.get or DBCursor.get, get_both,
first, last, next or prev encounter a DB_NOTFOUND
error they return None instead of raising DBNotFoundError.
This behaviour emulates Python dictionaries and is
convenient for looping.
You can use this method to toggle that behaviour for
all of the aformentioned methods or extend it to also
apply to the DBCursor.set, set_both, set_range, and
set_recno methods. Supported values of flag:
- **0** all DB and DBCursor get and set methods will
raise a DBNotFoundError rather than returning None.
- **1** *Default in module version <4.2.4* The DB.get
and DBCursor.get, get_both, first, last, next and
prev methods return None.
- **2** *Default in module version >=4.2.4* Extends the
behaviour of **1** to the DBCursor set, set_both,
set_range and set_recno methods.
The default of returning None makes it easy to do
things like this without having to catch DBNotFoundError
(KeyError)::
data = mydb.get(key)
if data:
doSomething(data)
or this::
rec = cursor.first()
while rec:
print rec
rec = cursor.next()
Making the cursor set methods return None is useful
in order to do this::
rec = mydb.set()
while rec:
key, val = rec
doSomething(key, val)
rec = mydb.next()
The downside to this it that it is inconsistent with
the rest of the package and noticeably diverges from
the Oracle Berkeley DB API. If you prefer to have the get and
set methods raise an exception when a key is not found,
use this method to tell them to do so.
Calling this method on a DBEnv object will set the default
for all DB's later created within that environment.
Calling it on a DB object sets the behaviour for that
DB only.
The previous setting is returned.
set_lg_bsize(size): --
Set the size of the in-memory log buffer, in bytes.
"More info...":api_c/env_set_lg_bsize.html
set_lg_dir(dir): --
The path of a directory to be used as the location of
logging files. Log files created by the Log Manager
subsystem will be created in this directory.
"More info...":api_c/env_set_lg_dir.html
set_lg_max(size): --
Set the maximum size of a single file in the log, in
bytes.
"More info...":api_c/env_set_lg_max.html
set_lg_regionmax(size): --
Set the maximum size of a single region in the log, in
bytes.
"More info...":api_c/env_set_lg_regionmax.html
set_lk_detect(mode): --
Set the automatic deadlock detection mode
"More info...":api_c/env_set_lk_detect.html
set_lk_max(max): --
Set the maximum number of locks. (This method is
deprecated.)
"More info...":api_c/env_set_lk_max.html
set_lk_max_locks(max): --
Set the maximum number of locks supported by the
Berkeley DB lock subsystem.
"More info...":api_c/env_set_lk_max_locks.html
set_lk_max_lockers(max): --
Set the maximum number of simultaneous locking
entities supported by the Berkeley DB lock subsystem.
"More info...":api_c/env_set_lk_max_lockers.html
set_lk_max_objects(max): --
Set the maximum number of simultaneously locked
objects supported by the Berkeley DB lock subsystem.
"More info...":api_c/env_set_lk_max_lockers.html
set_mp_mmapsize(size): --
Files that are opened read-only in the memory pool
(and that satisfy a few other criteria) are, by
default, mapped into the process address space instead
of being copied into the local cache. This can result
in better-than-usual performance, as available virtual
memory is normally much larger than the local cache,
and page faults are faster than page copying on many
systems. However, in the presence of limited virtual
memory it can cause resource starvation, and in the
presence of large databases, it can result in immense
process sizes.
This method sets the maximum file size, in bytes, for
a file to be mapped into the process address space.
If no value is specified, it defaults to 10MB.
"More info...":api_c/env_set_mp_mmapsize.html
log_archive(flags=0): --
Returns a list of log or database file names. By
default, log_archive returns the names of all of the
log files that are no longer in use (e.g., no longer
involved in active transactions), and that may safely
be archived for catastrophic recovery and then removed
from the system.
"More info...":api_c/log_archive.html
lock_detect(atype, flags=0): --
Run one iteration of the deadlock detector, returns
the number of transactions aborted.
"More info...":api_c/lock_detect.html
lock_get(locker, obj, lock_mode, flags=0): --
Aquires a lock and returns a handle to it as a DBLock
object. The locker parameter is an integer
representing the entity doing the locking, and obj is a
string representing the item to be locked.
"More info...":api_c/lock_get.html
lock_id(): --
Aquires a locker id, guaranteed to be unique across
all threads and processes that have the DBEnv open.
"More info...":api_c/lock_id.html
lock_put(lock): --
Release the lock.
"More info...":api_c/lock_put.html
lock_stat(flags=0): --
Returns a dictionary of locking subsystem statistics
with the following keys:
|-----------------------------------------------------|
| lastid | Last allocated lock ID. |
|-----------------------------------------------------|
| nmodes | Number of lock modes. |
|-----------------------------------------------------|
| maxlocks | Maximum number of locks possible. |
|-----------------------------------------------------|
| maxlockers | Maximum number of lockerspossible. |
|-----------------------------------------------------|
| maxobjects | Maximum number of objects possible. |
|-----------------------------------------------------|
| nlocks | Number of current locks. |
|-----------------------------------------------------|
| maxnlocks | Maximum number of locks at once. |
|-----------------------------------------------------|
| nlockers | Number of current lockers. |
|-----------------------------------------------------|
| nobjects | Number of current objects. |
|-----------------------------------------------------|
| maxnobjects | Maximum number of objects at once. |
|-----------------------------------------------------|
| maxnlockers | Maximum number of lockers at once. |
|-----------------------------------------------------|
| nrequests | Total number of locks requested. |
|-----------------------------------------------------|
| nreleases | Total number of locks released. |
|-----------------------------------------------------|
| nnowaits | Total number of lock requests that |
| | failed because of DB_LOCK_NOWAIT. |
|-----------------------------------------------------|
| nconflicts | Tot number of locks not immediately |
| | available due to conflicts. |
|-----------------------------------------------------|
| ndeadlocks | Number of deadlocks detected. |
|-----------------------------------------------------|
| regsize | Size of the region. |
|-----------------------------------------------------|
| region_wait | Number of times a thread of control |
| | was forced to wait before obtaining |
| | the region lock. |
|-----------------------------------------------------|
| region_nowait | Number of times a thread of control |
| | was able to obtain the region lock |
| | without waiting. |
|-----------------------------------------------------|
"More info...":api_c/lock_stat.html
set_tx_max(max): --
Set the maximum number of active transactions
"More info...":api_c/env_set_tx_max.html
txn_begin(parent=None, flags=0): --
Creates and begins a new transaction. A DBTxn object
is returned.
"More info...":api_c/txn_begin.html
txn_checkpoint(kbyte=0, min=0, flag=0): --
Flushes the underlying memory pool, writes a
checkpoint record to the log and then flushes the log.
"More info...":api_c/txn_checkpoint.html
txn_stat(): --
Return a dictionary of transaction statistics with the
following keys:
|------------------------------------------------------------|
| time_ckp | Time the last completed checkpoint finished |
| | (as the number of seconds since the Epoch, |
| | returned by the IEEE/ANSI Std 1003.1 POSIX |
| | time interface). |
|------------------------------------------------------------|
| last_txnid | Last transaction ID allocated. |
|------------------------------------------------------------|
| maxtxns | Max number of active transactions possible. |
|------------------------------------------------------------|
| nactive | Number of transactions currently active. |
|------------------------------------------------------------|
| maxnactive | Max number of active transactions at once. |
|------------------------------------------------------------|
| nbegins | Number of transactions that have begun. |
|------------------------------------------------------------|
| naborts | Number of transactions that have aborted. |
|------------------------------------------------------------|
| ncommits | Number of transactions that have committed. |
|------------------------------------------------------------|
| regsize | Size of the region. |
|------------------------------------------------------------|
| region_wait | Number of times that a thread of control |
| | was forced to wait before obtaining the |
| | region lock. |
|------------------------------------------------------------|
| region_nowait| Number of times that a thread of control |
| | was able to obtain the region lock without |
| | waiting. |
|------------------------------------------------------------|
"More info...":api_c/txn_stat.html
DB Methods
DB(dbEnv=None, flags=0) --
Constructor.
"More info...":api_c/db_create.html
append(data, txn=None) --
A convenient version of put() that can be used for
Recno or Queue databases. The DB_APPEND flag is
automatically used, and the record number is
returned.
"More info...":api_c/db_put.html#DB_APPEND
associate(secondaryDB, callback, flags=0) --
Used to associate secondaryDB to act as a secondary
index for this (primary) database. The callback
parameter should be a reference to a Python callable
object that will consruct and return the secondary key
or DB_DONOTINDEX if the item should not be indexed.
The parameters the callback will receive are the
primaryKey and primaryData values.
"More info...":api_c/db_associate.html
close(flags=0) --
Flushes cached data and closes the database
"More info...":api_c/db_close.html
consume(txn=None, flags=0) --
For a database with the Queue access method, returns
the record number and data from the first available
record and deletes it from the queue.
"More info...":api_c/db_get.html#DB_CONSUME
consume_wait(txn=None, flags=0) --
For a database with the Queue access method, returns
the record number and data from the first available
record and deletes it from the queue. If the Queue
database is empty, the thread of control will wait
until there is data in the queue before returning.
"More info...":api_c/db_get.html#DB_CONSUME_WAIT
cursor(txn=None, flags=0) --
Create a cursor on the DB and returns a DBCursor
object. If a transaction is passed then the cursor
can only be used within that transaction and you
*must* be sure to close the cursor before commiting
the transaction.
"More info...":api_c/db_cursor.html
delete(key, txn=None, flags=0) --
Removes a key/data pair from the database
"More info...":api_c/db_del.html
fd() --
Returns a file descriptor for the database
"More info...":api_c/db_fd.html
get(key, default=None, txn=None, flags=0, dlen=-1, doff=-1) --
Returns the data object associated with key. If key
is an integer then the DB_SET_RECNO flag is
automatically set for BTree databases and the actual
key and the data value are returned as a tuple. If
default is given then it is returned if the key is not
found in the database. Partial records can be read
using dlen and doff, however be sure to not read
beyond the end of the actual data or you may get
garbage.
"More info...":api_c/db_get.html
get_both(key, data, txn=None, flags=0) --
A convenient version of get() that automatically sets
the DB_GET_BOTH flag, and which will be successful
only if both the key and data value are found in the
database. (Can be used to verify the presence of a
record in the database when duplicate keys are
allowed.)
"More info...":api_c/db_get.html#DB_GET_BOTH
get_byteswapped() --
May be used to determine if the database was created
on a machine with the same endianess as the current
machine.
"More info...":api_c/db_get_byteswapped.html
get_size(key, txn=None) --
Return the size of the data object associated with key.
get_type() --
Return the database's access method type
"More info...":api_c/db_get_type.html
join(cursorList, flags=0) --
Create and return a specialized cursor for use in
performing joins on secondary indices
"More info...":api_c/db_join.html
key_range(key, txn=None, flags=0) --
Returns an estimate of the proportion of keys that are
less than, equal to and greater than the specified key.
"More info...":api_c/db_key_range.html
open(filename, dbname=None, dbtype=DB_UNKNOWN, flags=0, mode=0660) --
Opens the database named dbname in the file named
fileName. The dbname argument is optional and allows
applications to have multiple logical databases in a
single physical file. It is an error to attempt to
open a second database in a file that was not
initially created using a database name. In-memory
databases never intended to be shared or preserved on
disk may be created by setting both the fileName and
dbName arguments to None.
"More info...":api_c/db_open.html
put(key, data, txn=None, flags=0, dlen=-1, doff=-1) --
Stores the key/data pair in the database. If the
DB_APPEND flag is used and the database is using the
Recno or Queue access method then the record number
allocated to the data is returned. Partial data
objects can be written using dlen and doff.
"More info...":api_c/db_put.html
remove(filename, dbname=None, flags=0) --
Remove a database
"More info...":api_c/db_remove.html
rename(filename, dbname, newname, flags=0) --
Rename a database
"More info...":api_c/db_rename.html
set_bt_compare(compareFunc) --
Set the B-Tree database comparison function. This
can only be called once before the database has
been opened. compareFunc takes two arguments:
(left key string, right key string)
It must return a -1, 0, 1 integer similar to cmp.
You can shoot your database in the foot, beware!
Read the BerkeleyDB docs for the full details of
how the comparison function MUST behave.
"More info...":api_c/db_set_bt_compare.html
set_bt_minkey(minKeys) --
Set the minimum number of keys that will be stored on
any single BTree page
"More info...":api_c/db_set_bt_minkey.html
set_cachesize(gbytes, bytes, ncache=0) --
Set the size of the database's shared memory buffer pool
"More info...":api_c/db_set_cachesize.html
set_get_returns_none(flag): --
Controls what get and related methods do when a key is
not found.
See the DBEnv set_get_returns_none documentation.
The previous setting is returned.
set_flags(flags) --
Set additional flags on the database before opening.
"More info...":api_c/db_set_flags.html
set_h_ffactor(ffactor) --
Set the desired density within the hash table
"More info...":api_c/db_set_h_ffactor.html
set_h_nelem(nelem) --
Set an estimate of the final size of the hash table
"More info...":api_c/db_set_h_nelem.html
set_lorder(lorder) --
Set the byte order for integers in the stored database
metadata.
"More info...":api_c/db_set_lorder.html
set_pagesize(pagesize) --
Set the size of the pages used to hold items in the
database, in bytes.
"More info...":api_c/db_set_pagesize.html
set_re_delim(delim) --
Set the delimiting byte used to mark the end of a
record in the backing source file for the Recno access
method.
"More info...":api_c/db_set_re_delim.html
set_re_len(length) --
For the Queue access method, specify that the records
are of length length. For the Recno access method,
specify that the records are fixed-length, not byte
delimited, and are of length length.
"More info...":api_c/db_set_re_len.html
set_re_pad(pad) --
Set the padding character for short, fixed-length
records for the Queue and Recno access methods.
"More info...":api_c/db_set_re_pad.html
set_re_source(source) --
Set the underlying source file for the Recno access method
"More info...":api_c/db_set_re_source.html
set_q_extentsize(extentsize) --
Set the size of the extents used to hold pages in a
Queue database, specified as a number of pages. 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.
"More info...":api_c/db_set_q_extentsize.html
stat(flags=0) -- Return a dictionary containing database
statistics with the following keys.
For Hash databases:
|-------------------------------------------------------------|
| magic | Magic number that identifies the file as a Hash |
| | database. |
|-------------------------------------------------------------|
| version | Version of the Hash database. |
|-------------------------------------------------------------|
| nkeys | Number of unique keys in the database. |
|-------------------------------------------------------------|
| ndata | Number of key/data pairs in the database. |
|-------------------------------------------------------------|
| pagesize | Underlying Hash database page (& bucket) size. |
|-------------------------------------------------------------|
| nelem | Estimated size of the hash table specified at |
| | database creation time. |
|-------------------------------------------------------------|
| ffactor | Desired fill factor (number of items per bucket)|
| | specified at database creation time. |
|-------------------------------------------------------------|
| buckets | Number of hash buckets. |
|-------------------------------------------------------------|
| free | Number of pages on the free list. |
|-------------------------------------------------------------|
| bfree | Number of bytes free on bucket pages. |
|-------------------------------------------------------------|
| bigpages | Number of big key/data pages. |
|-------------------------------------------------------------|
| big_bfree | Number of bytes free on big item pages. |
|-------------------------------------------------------------|
| overflows | Number of overflow pages (overflow pages are |
| | pages that contain items that did not fit in |
| | the main bucket page). |
|-------------------------------------------------------------|
| ovfl_free | Number of bytes free on overflow pages. |
|-------------------------------------------------------------|
| dup | Number of duplicate pages. |
|-------------------------------------------------------------|
| dup_free | Number of bytes free on duplicate pages. |
|-------------------------------------------------------------|
For BTree and Recno databases:
|-------------------------------------------------------------|
| magic | Magic number that identifies the file as a |
| | Btree database. |
|-------------------------------------------------------------|
| version | Version of the Btree database. |
|-------------------------------------------------------------|
| nkeys | For the Btree Access Method, the number of |
| | unique keys in the database. |
| | For the Recno Access Method, the number of |
| | records in the database. If the database has |
| | been configured to not re-number records |
| | during deletion, the number of records may |
| | include records that have been deleted. |
|-------------------------------------------------------------|
| ndata | For the Btree Access Method, the number of |
| | key/data pairs in the database, |
| | For the Recno Access Method, the number of |
| | records in the database. If the database has |
| | been configured to not re-number records |
| | during deletion, the number of records may |
| | include records that have been deleted. |
|-------------------------------------------------------------|
| pagesize | Underlying database page size. |
|-------------------------------------------------------------|
| minkey | Minimum keys per page. |
|-------------------------------------------------------------|
| re_len | Length of fixed-length records. |
|-------------------------------------------------------------|
| re_pad | Padding byte value for fixed-length records. |
|-------------------------------------------------------------|
| levels | Number of levels in the database. |
|-------------------------------------------------------------|
| int_pg | Number of database internal pages. |
|-------------------------------------------------------------|
| leaf_pg | Number of database leaf pages. |
|-------------------------------------------------------------|
| dup_pg | Number of database duplicate pages. |
|-------------------------------------------------------------|
| over_pg | Number of database overflow pages. |
|-------------------------------------------------------------|
| free | Number of pages on the free list. |
|-------------------------------------------------------------|
| int_pgfree | Num of bytes free in database internal pages. |
|-------------------------------------------------------------|
| leaf_pgfree | Number of bytes free in database leaf pages. |
|-------------------------------------------------------------|
| dup_pgfree | Num bytes free in database duplicate pages. |
|-------------------------------------------------------------|
| over_pgfree | Num of bytes free in database overflow pages. |
|-------------------------------------------------------------|
For Queue databases:
|-------------------------------------------------------------|
| magic | Magic number that identifies the file as a |
| | Queue database. |
|-------------------------------------------------------------|
| version | Version of the Queue file type. |
|-------------------------------------------------------------|
| nkeys | Number of records in the database. |
|-------------------------------------------------------------|
| ndata | Number of records in the database. |
|-------------------------------------------------------------|
| pagesize | Underlying database page size. |
|-------------------------------------------------------------|
| pages | Number of pages in the database. |
|-------------------------------------------------------------|
| re_len | Length of the records. |
|-------------------------------------------------------------|
| re_pad | Padding byte value for the records. |
|-------------------------------------------------------------|
| pgfree | Number of bytes free in database pages. |
|-------------------------------------------------------------|
| start | Start offset. |
|-------------------------------------------------------------|
| first_recno | First undeleted record in the database. |
|-------------------------------------------------------------|
| cur_recno | Last allocated record number in the database. |
|-------------------------------------------------------------|
"More info...":api_c/db_stat.html
sync(flags=0) --
Flushes any cached information to disk
"More info...":api_c/db_sync.html
truncate(txn=None, flags=0) --
Empties the database, discarding all records it
contains. The number of records discarded from the
database is returned.
"More info...":api_c/db_truncate.html
upgrade(filename, flags=0) --
Upgrades all of the databases included in the file
filename, if necessary.
"More info...":api_c/db_upgrade.html
verify(filename, dbname=None, outfile=None, flags=0) --
Verifies the integrity of all databases in the file
specified by the filename argument, and optionally
outputs the databases' key/data pairs to a file.
"More info...":api_c/db_verify.html
DB Mapping and Compatibility Methods
These methods of the DB type are for implementing the Mapping
Interface, as well as others for making a DB behave as much
like a dictionary as possible. The main downside to using a
DB as a dictionary is you are not able to specify a transaction
object.
DB_length() [ usage: len(db) ] --
Return the number of key/data pairs in the database.
DB_subscript(key) [ usage: db[key] ] --
Return the data associated with key.
DB_ass_sub(key, data) [ usage: db[key] = data ] --
Assign or update a key/data pair, or delete a key/data
pair if data is NULL.
keys(txn=None) --
Return a list of all keys in the database. Warning:
this method traverses the entire database so it can
possibly take a long time to complete.
items(txn=None) --
Return a list of tuples of all key/data pairs in the
database. Warning: this method traverses the entire
database so it can possibly take a long time to
complete.
values(txn=None) --
Return a list of all data values in the database.
Warning: this method traverses the entire database so
it can possibly take a long time to complete.
has_key(key, txn=None) --
Returns true if key is present in the
database.
DBCursor Methods
close() --
Discards the cursor. If the cursor is created within
a transaction then you *must* be sure to close the
cursor before commiting the transaction.
"More info...":api_c/dbc_close.html
count(flags=0) --
Returns a count of the number of duplicate data items
for the key referenced by the cursor.
"More info...":api_c/dbc_count.html
delete(flags=0) --
Deletes the key/data pair currently referenced by the
cursor.
"More info...":api_c/dbc_del.html
dup(flags=0) --
Create a new cursor
"More info...":api_c/dbc_del.html
put(key, data, flags=0, dlen=-1, doff=-1) --
Stores the key/data pair into the database. Partial data
records can be written using dlen and doff.
"More info...":api_c/dbc_put.html
get(flags, dlen=-1, doff=-1) --
See get(key, data, flags, dlen=-1, doff=-1) below.
get(key, flags, dlen=-1, doff=-1) --
See get(key, data, flags, dlen=-1, doff=-1) below.
get(key, data, flags, dlen=-1, doff=-1) --
Retrieves key/data pairs from the database using the
cursor. All the specific functionalities of the get
method are actually provided by the various methods
below, which are the preferred way to fetch data
using the cursor. These generic interfaces are only
provided as an inconvenience. Partial data records are
returned if dlen and doff are used in this method and in
many of the specific methods below.
"More info...":api_c/dbc_get.html
DBCursor Get Methods
These DBCursor methods are all wrappers around the get()
function in the C API.
current(flags=0, dlen=-1, doff=-1) --
Returns the key/data pair currently referenced by the
cursor.
"More info...":api_c/dbc_get.html#DB_CURRENT
get_current_size() --
Returns length of the data for the current entry referenced
by the cursor.
first(flags=0, dlen=-1, doff=-1) --
Position the cursor to the first key/data pair and
return it.
"More info...":api_c/dbc_get.html#DB_FIRST
last(flags=0, dlen=-1, doff=-1) --
Position the cursor to the last key/data pair and
return it.
"More info...":api_c/dbc_get.html#DB_LAST
next(flags=0, dlen=-1, doff=-1) --
Position the cursor to the next key/data pair and
return it.
"More info...":api_c/dbc_get.html#DB_NEXT
prev(flags=0, dlen=-1, doff=-1) --
Position the cursor to the previous key/data pair and
return it.
"More info...":api_c/dbc_get.html#DB_PREV
consume(flags=0) --
For a database with the Queue access method, returns
the record number and data from the first available
record and deletes it from the queue.
*NOTE:* This method is deprecated in Berkeley DB
version 3.2 in favor of the new consume method in the
DB class.
get_both(key, data, flags=0) --
Like set() but positions the cursor to the record
matching both key and data. (An alias for this is
set_both, which makes more sense to me...)
"More info...":api_c/dbc_get.html#DB_GET_BOTH
get_recno() --
Return the record number associated with the cursor.
The database must use the BTree access method and have
been created with the DB_RECNUM flag.
"More info...":api_c/dbc_get.html#DB_GET_RECNO
join_item() --
For cursors returned from the DB.join method, returns
the combined key value from the joined cursors.
"More info...":api_c/dbc_get.html#DB_JOIN_ITEM
next_dup(flags=0, dlen=-1, doff=-1) --
If the next key/data pair of the database is a
duplicate record for the current key/data pair, the
cursor is moved to the next key/data pair of the
database, and that pair is returned.
"More info...":api_c/dbc_get.html#DB_NEXT_DUP
next_nodup(flags=0, dlen=-1, doff=-1) --
The cursor is moved to the next non-duplicate key/data
pair of the database, and that pair is returned.
"More info...":api_c/dbc_get.html#DB_NEXT_NODUP
prev_nodup(flags=0, dlen=-1, doff=-1) --
The cursor is moved to the previous non-duplicate
key/data pair of the database, and that pair is
returned.
"More info...":api_c/dbc_get.html#DB_PREV_NODUP
set(key, flags=0, dlen=-1, doff=-1) --
Move the cursor to the specified key in the database
and return the key/data pair found there.
"More info...":api_c/dbc_get.html#DB_SET
set_range(key, flags=0, dlen=-1, doff=-1) --
Identical to set() except that in the case of the BTree
access method, the returned key/data pair is the
smallest key greater than or equal to the specified
key (as determined by the comparison function),
permitting partial key matches and range searches.
"More info...":api_c/dbc_get.html#DB_SET_RANGE
set_recno(recno, flags=0, dlen=-1, doff=-1) --
Move the cursor to the specific numbered record of the
database, and return the associated key/data pair.
The underlying database must be of type Btree and it
must have been created with the DB_RECNUM flag.
"More info...":api_c/dbc_get.html#DB_SET_RECNO
set_both(key, data, flags=0) --
See get_both(). The only difference in behaviour
can be disabled using set_get_returns_none(2).
"More info...":api_c/dbc_get.html#DB_GET_BOTH
DBTxn Methods
abort() --
Aborts the transaction
"More info...":api_c/txn_abort.html
commit(flags=0) --
Ends the transaction, committing any changes to the
databases.
"More info...":api_c/txn_commit.html
id() --
The txn_id function returns the unique transaction id
associated with the specified transaction.
"More info...":api_c/txn_id.html
prepare(gid) --
Initiates the beginning of a two-phase commit.
Begining with BerkeleyDB 3.3 a global identifier
paramater is required, which is a value unique across
all processes involved in the commit. It must be a
string of DB_XIDDATASIZE bytes.
"More info...":api_c/txn_prepare.html
DBLock
The DBLock objects have no methods or attributes. They are
just opaque handles to the lock in question.
Document Version: $Id: bsddb3.txt 274 2007-10-01 04:52:36Z greg $
This is a StructuredTextNG document. To see the original, "click
here":bsddb3.txt
|