2026-03-29 2.2.0
#################

New features
------------

- New ``lmdb.aio`` module providing asyncio support with
    ``AsyncEnvironment`` and ``AsyncTransaction``. (#434)

- ``Environment.dbs()`` lists all named databases in an environment.
    (#253, #438)

- ``Cursor.getmulti()`` accepts ``values=False`` for batch key-existence
    checks without fetching values. (#435)

- ``Transaction.stat()`` now defaults to the main database when no ``db``
    argument is given. (#366, #439)

- ``Environment.set_mapsize()`` now safely invalidates open transactions
    and cursors before remapping, preventing use-after-free crashes. (#443)

- Enable sparse files on Windows so NTFS does not preallocate the full
    ``map_size`` on disk. (#444)

Bug fixes
---------

- Fix type stubs: return types now use ``Union[bytes, memoryview]`` to
    reflect the ``buffers=`` parameter, and ``dbs()`` is included. (#448, #449)

- Declare ``python_requires='>=3.9'`` so pip skips this package on
    Python 2. (#447)

Documentation
-------------

- Modernize documentation for Python 3 and current project state. (#436)

- Add API reference for ``lmdb.aio`` module. (#440)

- Document fork safety and multiprocessing guidance. (#441)

- Document duplicate-sort (dupsort) databases. (#442)

- Document cursor iteration and navigation patterns. (#445)

- Add "When to use py-lmdb" comparison section. (#446)

- Render ChangeLog as native HTML instead of a code block. (#451)

Other
-----

- Add LMDB data layout validation tests and patched/pure equivalence
    checks. (#433)

2026-03-19 2.1.1
################

- Fix false `MDB_CORRUPTED` error when overwriting values larger than the page
    size (overflow/bigdata values) with `txn.put(key, value, overwrite=True)`.
    Two hardening checks from 2.1.0 did not account for `F_BIGDATA` nodes where
    `NODEDSZ()` returns the logical data size, not the on-page size. (#431)

2026-03-19 2.1.0
################

**Security release.** All users who open LMDB databases from untrusted or
potentially-tampered sources should upgrade immediately. Applications that only
open databases they created themselves are not at risk, but upgrading is still
recommended for defense-in-depth.

Security fixes
--------------

The bundled LMDB 0.9.35 trusts many on-disk fields without validation. A
crafted `data.mdb` file can exploit this to crash the process, read arbitrary
memory, or corrupt the heap. These are all upstream LMDB bugs; py-lmdb ships
patches to address them.

- **CVE-2019-16224**: heap buffer overflow via `MDB_DUPFIXED` without
    `MDB_DUPSORT` in on-disk `md_flags`. (#429)

- **CVE-2019-16225**: `SIGSEGV` from `P_DIRTY` flag set on mmap'd disk pages,
    causing `mdb_page_touch()` to skip copy-on-write. (#429)

- **CVE-2019-16226**: out-of-bounds `memmove` in `mdb_node_del` via corrupt
    `mn_hi` making `NODEDSZ()` huge. (#429)

- **CVE-2019-16227**: NULL pointer dereference of `mc_xcursor` when
    `F_DUPDATA` is set on a node in a non-DUPSORT database. (#429)

- **CVE-2019-16228**: divide-by-zero from zero `mm_psize` in meta page
    header. (#429)

- **13 additional hardening patches** from variant analysis of the same code
    (#430), including:

    - Validate `mp_lower`/`mp_upper` bounds on every page fetch — prevents
      `NUMKEYS()` unsigned wrap and `SIZELEFT()` underflow.
    - Bounds-check `NODEDSZ()` in `mdb_node_read`, `mdb_cursor_put`, and
      `mdb_page_split` — prevents OOB reads and heap overflows from corrupt
      node sizes.
    - Validate DUPSORT sub-page headers before copying — prevents `memcpy`
      size underflow (unsigned wrap to huge value).
    - Check `NODEDSZ >= sizeof(MDB_db)` before `memcpy` in
      `mdb_xcursor_init1` — prevents read past node boundary.
    - Validate LEAF2 `mp_pad` (key size) — zero or huge values cause OOB
      via `LEAF2KEY()`.
    - Guard `mc_xcursor` NULL in `MDB_GET_CURRENT` and `_mdb_cursor_del` —
      two call sites missed by the CVE-2019-16227 fix.
    - Guard `nsize` underflow in `mdb_node_shrink`.
    - Validate overflow page extent (`pgno + mp_pages`) stays within the
      database.
    - Reject meta page numbers (0, 1) as B-tree roots.
    - Validate `md_depth <= CURSOR_STACK` to prevent stack buffer overrun.

Bug fixes
---------

- Cross-thread write transactions now block instead of raising
    `lmdb.Error("Attempt to operate on closed/deleted/dropped object.")`.
    The check added in 1.8.0 was overly strict: it rejected all concurrent
    write transactions, but only same-thread re-entrance is actually
    incorrect. The cpython implementation now releases the GIL during
    `mdb_txn_begin` for write transactions, allowing another thread to
    block until the first commits. (#427, #428)

Other
-----

- Refactored `setup.py` patch application into a single loop with a shared
    patch list, replacing duplicated `os.system()` blocks.

2026-03-17 2.0.0
################

This is the largest py-lmdb release in years, made possible by a new coding
partner: Claude (Anthropic). Nearly every change below was co-authored by
Claude, turning months of backlogged issues into a week of focused work.

Potentially breaking changes
----------------------------

- **Thread-safety overhaul (#180).** Environment.close(), Transaction.abort(),
    Transaction.commit(), and cursor operations are now serialized with locks
    to prevent use-after-free and double-free crashes when called concurrently.
    Code that previously "worked" by luck with racy close/abort patterns may
    now block where it previously crashed or silently corrupted memory. If you
    relied on the old undefined behavior, review your threading model.

- **Duplicate environment path rejection (#230).** Opening the same LMDB path
    twice in one process now raises lmdb.Error instead of silently proceeding
    to a likely segfault. This will surface latent bugs in code that
    accidentally opened the same environment twice.

- **Minimum Python version is now 3.9.** Python 2.7 and 3.5-3.8 are no longer
    supported. Python 2 compatibility shims have been removed from the
    codebase.

New features
------------

- PEP 561 type stubs (py.typed) are now shipped (#257). IDEs and type
    checkers will pick up lmdb's types automatically.

- Cache getpid() result to avoid a syscall on every transaction dealloc.
    Since glibc 2.25, getpid() is no longer cached in userspace; this showed
    up in profiles for workloads with many short-lived transactions.
    Contributed by @ltfish (#421).

Bug fixes
---------

- Fix memory safety issues across cpython and CFFI implementations (#420):
    multiple reference count leaks in cpython.c (env_readers_callback,
    db_flags, env_flags, env_copy, env_new, make_arg_cache, cursor_get_multi),
    a getmulti validation bug in cffi.py, and a cursor leak on
    mdb_cursor_open failure.

- Fix unsafe buffer protocol usage in cpython.c that could read freed memory
    (#372).

- Fix cmd_copyfd fd validation to use os.fstat() instead of os.fdopen(),
    which consumed the fd.

- Add fork detection to CFFI implementation. Previously, Transaction.__del__
    and Environment.__del__ would call mdb_txn_abort / mdb_env_close in forked
    child processes, risking corruption of the parent's environment.

- Release GIL during mdb_env_close (#418) so the event loop isn't blocked
    while msync/fsync runs on large writemap databases.

Other
-----

- Comprehensive test suite for lmdb.tool (#148).

- Fix ReadTheDocs build (#414, #172).

- Fix pyright errors and remove Python 2 compat code.

2026-03-12 1.8.1
################

- CI Fix

2026-03-12 1.8.0
################

- Update bundled LMDB from 0.9.33 to 0.9.35.

- Fix Windows heap corruption caused by recursive write mutex. Replace
    Windows Mutex objects with Semaphores for LMDB's read and write locks,
    preventing concurrent write transactions on the same thread.
    Reported by @RogueZamboni (#394).

- Fix infinite loop with next_nodup/prev_nodup on the sole key in a
    dupsort database after delete+put.
    Reported by @RogerMarsh (#388).

- Fix METH_NOARGS function signatures to include the required second
    parameter (CPython 3.14 compatibility).
    Reported by @dw (#182).

- Fix installing and running on PyPy.
    Reported by and fix contributed by @mgorny (#403).

- Fix PreloadTest on openSUSE. Contributed by @mgrossu (#400).

- CI-only: Fix PyPy wheel upload by adding auditwheel repair.

2025-10-14 1.7.5
################

- CI-only: Fix generation of 3.14 binaries.

2025-10-14 1.7.4 -- yanked
##########################

- CI-only: Generate Python 3.14 binaries.

2025-07-15 1.7.3
################

- Fix CFFI build on some platforms by ensuring paths are absolute.

- Correct CI badge URL in README.

2025-07-10 1.7.2
################

- CI-only fix

2025-07-09 1.7.1
################

- CI-only fix

2025-07-09 1.7.0
################

- Rewrite CI to use cibuildwheel.

- Update bundled LMDB to 0.9.33, plus a patch to fix ITS#10346.

- Prevent some accidental use of LMDB objects by child processes.
    Contributed by Callum Walker.

2025-01-05 1.6.2
################

- CI-only fix.

2025-01-05 1.6.1
################

- CI-only fix.

2025-01-05 1.6.0
################

- Support for Python 3.13. Contributed by Miro Hrončok and Adam Williamson.

- CI: Publish 3.13 binaries and Linux aarch64 wheels for multiple versions.

2024-07-01 1.5.1
################
- CI-only fix.

2024-06-30 1.5.0
################
- Add Python 3.12 binaries.

- Update bundled LMDB to 0.9.31.

- Remove Python 2.7 support.

2022-04-04 v1.4.1
#################
- Update CI to build manylinux binaries.

2022-12-06 v1.4.0
#################
- Add Python 3.11 support.

2021-12-30 v1.3.0
#################
- Add aarch64 architecture builds.  Contributed by odidev.

- Add Python 3.10 support.

- Fix crash relating to caching of transactions.  The 'max_spare_txns'
    parameter to Environment/open is currently ignored in cpython.

2021-04-19 v1.2.1
#################
- Resolve CI bug where non-Linux wheels were not being published to PyPI.

2021-04-15 v1.2.0
#################
- Update bundled LMDB to 0.9.29.

- Add non-bundled testing to CI.

- Remove wheel generation for 2.7 because the manylinux images no longer
    support it.

- Allow passing None as a value to transaction.del in CFFI implementation
    for parity with cpython implementation.

- Fix Cursor.put behavior on a dupsort DB with append=True.

- Add warning to docs about use of Environment.set_mapsize. This is currently
    an unresolved issue with upstream LMDB.

- CFFI implementation:  fix a seg fault when open_db returns map full.

- CFFI implementation:  fix a bug in open_db in a read-only environment.


2021-02-05 v1.1.1
#################
- Dowgrade underlying LMDB to 0.9.26.  0.9.27 has a minor defect that will
    need to get resolved.


2021-02-04 v1.1.0
#################
- Migrate CI pipeline from Travis and AppVeyor to Github Actions.  Now
    includes comprehensive testing across 4 dimensions (OS, Python version,
    cpython/CFFI, pure/with mods).  Also includes publishing to PyPI.

- Prevent invalid flag combinations when creating a database.

- Add a Cursor.getmulti method with optional buffer support.  Contributed by
    Will Thompson <willsthompson@gmail.com>.

- Upgrade underlying LMDB to 0.9.27.


2020-08-28 v1.0.0
#################
- Start of new semantic versioning scheme.  This would be a minor version
    bump from the 0.99 release if it were semantically versioned.

- Allow environment copy to take a passed-in transaction.  This is the
    first released feature that requires a (very small) patch to the
    underlying C library.  By default, the patch will be applied unless
    this module is built with LMDB_PURE environment variable set.


2020-08-13 v0.99
################
- Fix lmdb.tool encoding issues.

- Fix -l lmdb invocation issue.

- Minor documentation improvements.

- Update LMDB to version 0.9.24.

- Update for Python 3.9 (current release candidate) support.

- Resolve a bug when using cursor.putmulti and append=True on dupsort DBs.

- Allow _Database.flags method to take no arguments since the one argument
    wasn't being used.


2019-11-06 v0.98
################
- Fix that a duplicate argument to a lmdb method would cause an assert.

- Solaris needs ``#include "python.h"`` as soon as possible.  Fix
    contributed by Jesús Cea.

- Fix crash under debug cpython when mdb_cursor_open failed


2019-08-11 v0.97
################

- Fix a missed GIL unlock sequence.  Reported by ajschorr.

- Fix argv check in JEP (cpython under Java) environment.  Contributed by
    de-code.


2019-07-14 v0.96
################

- First release under new maintainer, Nic Watson.

- Doc updates.

- More removal of code for now-unsupported Python versions.

- Only preload the value with the GIL unlocked when the value is actually
    requested. This significantly improves read performance to retrieve keys
    with large values when the value isn't retrieved. Reported by Dan Patton.


2019-06-08 v0.95
################

- The minimum supported version of Python is now 2.7.

- The library is no longer tested on Python 3.2.

- The address-book.py example was updated for Python 3. Contributed by Jamie
    Bliss.

- Development-related files were removed from the distribution tarball.

- Handling of the Environment(create=True) flag was improved. Fix contributed
    by Nir Soffer.

- Database names may be reused after they are dropped on CFFI, without
    reopening the environment. Fix contributed by Gareth Bult.


2018-04-09 v0.94
################

- CPython argument parsing now matches the behaviour of CFFI, and most sane
    Python APIs: a bool parameter is considered to be true if it is any truthy
    value, not just if it is exactly True. Reported by Nic Watson.

- Removed Python 2.6 support due to urllib3 warnings and pytest dropping it.

- Updared LMDB to version 0.9.22.

- Fixed several 2.7/3 bugs in command line tool.


2017-07-16 v0.93
################

- py-lmdb is now built with AppVeyor CI, providing early feedback on Windows
    build health. Egg and wheel artifacts are being generated, removing the need
    for a dedicated Windows build machine, however there is no mechanism to
    paublish these to PyPI yet.

- The "warm" tool command did not function on Python 3.x. Reported by Github
    user dev351.

- Tests now pass on non-4kb page-sized machines, such as ppc64le. Reported by
    Jonathan J. Helmus.

- Windows 3.6 eggs and wheels are now available on PyPI, and tests are run
    against 3.6. Reported by Ofek Lev.

- Python 3.2 is no longer supported, due to yet more pointless breakage
    introduced in pip/pkg_resources.

- py-lmdb currently does not support LMDB >=0.9.19 due to interface changes in
    LMDB. Support will appear in a future release.


2016-10-17 v0.92
################

- Changes to support __all__ caused the CPython module to fail to import at
    runtime on Python 3. This was hidden during testing as the CFFI module was
    successfully imported.


2016-10-17 v0.91
################

- The docstring for NotFoundError was clarified to indicate that it is
    not raised in normal circumstances.

- CFFI open_db() would always attempt to use a write transaction, even if the
    environment was opened with readonly=True. Now both CPython and CFFI will
    use a read-only transaction in this case. Reported by Github user
    handloomweaver.

- The source distribution previously did not include a LICENSE file, and may
    have included random cached junk from the source tree during build. Reported
    by Thomas Petazzoni.

- Transaction.id() was broken on Python 2.5.

- Repair Travis CI build again.

- CFFI Cursor did not correctly return empty strings for key()/value()/item()
    when iternext()/iterprev() had reached the start/end of the database.
    Detected by tests contributed by Ong Teck Wu.

- The package can now be imported from within a CPython subinterpreter. Fix
    contributed by Vitaly Repin.

- lmdb.tool --delete would not delete keys in some circumstances. Fix
    contributed by Vitaly Repin.

- Calls to Cursor.set_range_dup() could lead to memory corruption due to
    Cursor's idea of the key and value failing to be updated correctly. Reported
    by Michael Lazarev.

- The lmdb.tool copy command now supports a --compact flag. Contributed by
    Achal Dave.

- The lmdb.tool edit command selects the correct database when --delete is
    specified. Contributed by ispequalnp.

- lmdb.tool correctly supports the -r flag to select a read-only environment.
    Contributed by ispequalnp.

- The lmdb.tool --txn_size parameter was removed, as it was never implemented,
    and its original function is no longer necessary with modern LMDB. Reported
    by Achal Dave.

- The documentation template was updated to fix broken links. Contributed by
    Adam Chainz.

- The Travis CI build configuration was heavily refactored by Alexander Zhukov.
    Automated tests are running under Travis CI once more.

- The CPython extension module did not define __all__. It is now defined
    contain the same names as on CFFI.

- Both implementations were updated to remove lmdb.open() from __all__,
    ensuring ``from lmdb import *`` does not shadow the builtin open(). The
    function can still be invoked using its fully qualified name, and the alias
    "Environment" may be used when ``from lmdb import *`` is used. Reported by
    Alexander Zhukov.

- The CPython extension exported BadRSlotError, instead of BadRslotError. The
    exception's name was corrected to match CFFI.

- Environment.open_db() now supports integerdup=True, dupfixed=True, and
    integerkey=True flags. Based on a patch by Jonathan Heyman.


2016-07-11 v0.90
################

- This release was deleted from PyPI due to an erroneous pull request
    upgrading the bundled LMDB to mdb.master.


2016-02-12 v0.89
################

- LMDB 0.9.18 is bundled.

- CPython Iterator.next() was incorrectly defined as pointing at the
    implementation for Cursor.next(), triggering a crash if the method was ever
    invoked manually. Reported by Kimikazu Kato.


2016-01-24 v0.88
################

- LMDB 0.9.17 is bundled.

- Transaction.id() is exposed.

- Binary wheels are built for Python 3.5 Windows 32/64-bit.


2015-08-11 v0.87
################

- Environment.set_mapsize() was added to allow runtime adjustment of the
    environment map size.

- Remove non-determinism from setup.py, to support Debian's reproducible
    builds project. Patch by Chris Lamb.

- Documentation correctness and typo fixes. Patch by Gustav Larsson.

- examples/keystore: beginnings of example that integrates py-lmdb with an
    asynchronous IO loop.


2015-06-07 v0.86
################

- LMDB_FORCE_SYSTEM builds were broken by the GIL/page fault change. This
    release fixes the problem.

- Various cosmetic fixes to documentation.


2015-06-06 v0.85
################

- New exception class: lmdb.BadDbiError.

- Environment.copy() and Environment.copyfd() now support compact=True, to
    trigger database compaction while copying.

- Various small documentation updates.

- CPython set_range_dup() and set_key_dup() both invoked MDB_GET_BOTH, however
    set_range_dup() should have instead invoked MDB_GET_BOTH_RANGE. Fix by
    Matthew Battifarano.

- lmdb.tool module was broken on Win32, since Win32 lacks signal.SIGWINCH. Fix
    suggested by David Khess.

- LMDB 0.9.14 is bundled along with extra fixes from mdb.RE/0.9 (release
    engineering) branch.

- CPython previously lacked a Cursor.close() method. Problem was noticed by
    Jos Vos.

- Several memory leaks affecting the CFFI implementation when running on
    CPython were fixed, apparent only when repeatedly opening and discarding a
    large number of environments. Noticed by Jos Vos.

- The CPython extension previously did not support weakrefs on Environment
    objects, and the implementation for Transaction objects was flawed. The
    extension now correctly invalidates weakrefs during deallocation.

- Both variants now try to avoid taking page faults with the GIL held,
    accomplished by touching one byte of every page in a value during reads.
    This does not guarantee faults will never occur with the GIL held, but it
    drastically reduces the possibility. The binding should now be suitable for
    use in multi-threaded applications with databases containing >2KB values
    where the entire database does not fit in RAM.


2014-09-22 v0.84
################

- LMDB 0.9.14 is bundled.

- CFFI Cursor.putmulti() could crash when append=False and a key already
    existed.


2014-06-24 v0.83
################

- LMDB 0.9.13 is bundled along with extra fixes from upstream Git.

- Environment.__enter__() and __exit__() are implemented, allowing
    Environments to behave like context managers.

- Cursor.close(), __enter__() and __exit__() are implemented, allowing Cursors
    to be explicitly closed. In CFFI this mechanism *must* be used when many
    cursors are used within a single transaction, otherwise a resource leak will
    occur.

- Dependency tracking in CFFI is now much faster, especially on PyPy, however
    at a cost: Cursor use must always be wrapped in a context manager, or
    .close() must be manually invoked for discarded Cursors when the parent
    transaction is long lived.

- Fixed crash in CFFI Cursor.putmulti().


2014-05-26 v0.82
################

- Both variants now implement max_spare_txns, reducing the cost of creating a
    read-only transaction 4x for an uncontended database and by up to 20x for
    very read-busy environments. By default only 1 read-only transaction is
    cached, adjust max_spare_txns= parameter if your script operates multiple
    simultaneous read transactions.

- Patch from Vladimir Vladimirov implementing MDB_NOLOCK.

- The max_spare_iters and max_spare_cursors parameters were removed, neither
    ever had any effect.

- Cursor.putmulti() implemented based on a patch from Luke Kenneth Casson
    Leighton. This function moves the loop required to batch populate a
    database out of Python and into C.

- The bundled LMDB 0.9.11 has been updated with several fixes from upstream
    Git.

- The cost of using keyword arguments in the CPython extension was
    significantly reduced.


2014-04-26 v0.81
################

- On Python 2.x the extension module would silently interpret Unicode
    instances as buffer objects, causing UCS-2/UCS-4 string data to end up in
    the database. This was never intentional and now raises TypeError. Any
    Unicode data passed to py-lmdb must explicitly be encoded with .encode()
    first.

- open_db()'s name argument was renamed to key, and its semantics now match
    get() and put(): in other words the key must be a bytestring, and passing
    Unicode will raise TypeError.

- The extension module now builds under Python 3.4 on Windows.


2014-04-21 v0.80
################

- Both variants now build successfully as 32 bit / 64bit binaries on
    Windows under Visual Studio 9.0, the compiler for Python 2.7. This enables
    py-lmdb to be installed via pip on Windows without requiring a compiler to
    be available. In future, .egg/.whl releases will be pre-built for all recent
    Python versions on Windows.

    Known bugs: Environment.copy() and Environment.copyfd() currently produce a
    database that cannot be reopened.

- The lmdb.enable_drop_gil() function was removed. Its purpose was
    experimental at best, confusing at worst.


2014-03-17 v0.79
################

- CPython Cursor.delete() lacked dupdata argument, fixed.

- Fixed minor bug where CFFI _get_cursor() did not note its idea of
    the current key and value were up to date.

- Cursor.replace() and Cursor.pop() updated for MDB_DUPSORT databases. For
    pop(), the first data item is popped and returned. For replace(), the first
    data item is returned, and all duplicates for the key are replaced.

- Implement remaining Cursor methods necessary for working with MDB_DUPSORT
    databases: next_dup(), next_nodup(), prev_dup(), prev_nodup(), first_dup(),
    last_dup(), set_key_dup(), set_range_dup(), iternext_dup(),
    iternext_nodup(), iterprev_dup(), iterprev_nodup().

- The default for Transaction.put(dupdata=...) and Cursor.put(dupdata=...) has
    changed from False to True. The previous default did not reflect LMDB's
    normal mode of operation.

- LMDB 0.9.11 is bundled along with extra fixes from upstream Git.


2014-01-18 v0.78
################

- Patch from bra-fsn to fix LMDB_LIBDIR.

- Various inaccurate documentation improvements.

- Initial work towards Windows/Microsoft Visual C++ 9.0 build.

- LMDB 0.9.11 is now bundled.

- To work around install failures minimum CFFI version is now >=0.8.0.

- ticket #38: remove all buffer object hacks. This results in ~50% slowdown
    for cursor enumeration, but results in far simpler object lifetimes. A
    future version may introduce a better mechanism for achieving the same
    performance without loss of sanity.


2013-11-30 v0.77
################

- Added Environment.max_key_size(), Environment.max_readers().

- CFFI now raises the correct Error subclass associated with an MDB_* return
    code.

- Numerous CFFI vs. CPython behavioural inconsistencies have been fixed.

- An endless variety of Unicode related 2.x/3.x/CPython/CFFI fixes were made.

- LMDB 0.9.10 is now bundled, along with some extra fixes from Git.

- Added Environment(meminit=...) option.


2013-10-28 v0.76
################

- Added support for Environment(..., readahead=False).

- LMDB 0.9.9 is now bundled.

- Many Python 2.5 and 3.x fixes were made. Future changes are automatically
    tested via Travis CI <https://travis-ci.org/dw/py-lmdb>.

- When multiple cursors exist, and one cursor performs a mutation,
    remaining cursors may have returned corrupt results via key(), value(),
    or item(). Mutations are now explicitly tracked and cause the cursor's
    data to be refreshed in this case.

- setup.py was adjusted to ensure the distutils default of '-DNDEBUG' is never
    defined while building LMDB. This caused many important checks in the engine
    to be disabled.

- The old 'transactionless' API was removed. A future version may support the
    same API, but the implementation will be different.

- Transaction.pop() and Cursor.pop() helpers added, to complement
    Transaction.replace() and Cursor.replace().
