ChangeLog
---------

### TODO

 - [Engage an "overlapped I/O" on Windows](https://github.com/erthink/libmdbx/issues/224).
 - [Simple careful mode for working with corrupted DB](https://github.com/erthink/libmdbx/issues/223).
 - [Move most of `mdbx_chk` functional to the library API](https://github.com/erthink/libmdbx/issues/204).
 - [Replace SRW-lock on Windows to allow shrink DB with `MDBX_NOTLS` option](https://github.com/erthink/libmdbx/issues/210).
 - [More flexible support of asynchronous runtime/framework(s)](https://github.com/erthink/libmdbx/issues/200).
 - [Migration guide from LMDB to MDBX](https://github.com/erthink/libmdbx/issues/199).
 - [Get rid of dirty-pages list in MDBX_WRITEMAP mode](https://github.com/erthink/libmdbx/issues/193).
 - [Large/Overflow pages accounting for dirty-room](https://github.com/erthink/libmdbx/issues/192).
 - [Support for RAW devices](https://github.com/erthink/libmdbx/issues/124).
 - [Support MessagePack for Keys & Values](https://github.com/erthink/libmdbx/issues/115).
 - [Engage new terminology](https://github.com/erthink/libmdbx/issues/137).
 - Finalize C++ API (there is still a small chance for a few typos and bugs).
 - Packages for [Astra Linux](https://astralinux.ru/), [ALT Linux](https://www.altlinux.org/), [ROSA Linux](https://www.rosalinux.ru/), etc.


## v0.11.2 (underway)

Acknowledgements:

 - [장세연 (Чан Се Ен)](https://github.com/sasgas) for contributing to C++ API.

Minors:

 - Fixed `constexpr`-related macros for legacy compilers.
 - Allowed to define 'CMAKE_CXX_STANDARD` using an environment variable.
 - Simplified collection statistics of page operation .
 - [Fixed](https://github.com/erthink/libmdbx/pull/239) compilation with devtoolset-9 on CentOS/RHEL 7.


## v0.11.1 at 2021-10-23

### Backward compatibility break:

The database format signature has been changed to prevent
forward-interoperability with an previous releases, which may lead to a
[false positive diagnosis of database corruption](https://github.com/erthink/libmdbx/issues/238)
due to flaws of an old library versions.

This change is mostly invisible:

 - previously versions are unable to read/write a new DBs;
 - but the new release is able to handle an old DBs and will silently upgrade ones.

Acknowledgements:

 - [Alex Sharov](https://github.com/AskAlexSharov) for reporting and testing.


## v0.10.5 at 2021-10-13 (obsolete, please use v0.11.1)

Unfortunately, the `v0.10.5` accidentally comes not full-compatible with previous releases:

 - `v0.10.5` can read/processing DBs created by previous releases, i.e. the backward-compatibility is provided;
 - however, previous releases may lead to false-corrupted state with DB that was touched by `v0.10.5`, i.e. the forward-compatibility is broken for `v0.10.4` and earlier.

This cannot be fixed, as it requires fixing past versions, which as a result we will just get a current version.
Therefore, it is recommended to use `v0.11.1` instead of `v0.10.5`.

Acknowledgements:

 - [Noel Kuntze](https://github.com/Thermi) for immediately bug reporting.

Fixes:

 - Fixed unaligned access regression after the `#pragma pack` fix for modern compilers.
 - Added UBSAN-test to CI to avoid a regression(s) similar to lately fixed.
 - Fixed possibility of meta-pages clashing after manually turn to a particular meta-page using `mdbx_chk` utility.

Minors:

 - Refined handling of weak or invalid meta-pages while a DB opening.
 - Refined providing information for the @MAIN and @GC sub-databases of a last committed modification transaction's ID.


## v0.10.4 at 2021-10-10

Acknowledgements:

 - [Artem Vorotnikov](https://github.com/vorot93) for support [Rust wrapper](https://github.com/vorot93/mdbx-rs).
 - [Andrew Ashikhmin](https://github.com/yperbasis) for contributing to C++ API.

Fixes:

 - Fixed possibility of looping update GC during transaction commit (no public issue since the problem was discovered inside [Positive Technologies](https://www.ptsecurity.ru)).
 - Fixed `#pragma pack` to avoid provoking some compilers to generate code with [unaligned access](https://github.com/erthink/libmdbx/issues/235).
 - Fixed `noexcept` for potentially throwing `txn::put()` of C++ API.

Minors:

 - Added stochastic test script for checking small transactions cases.
 - Removed extra transaction commit/restart inside test framework.
 - In debugging builds fixed a too small (single page) by default DB shrink threshold.


## v0.10.3 at 2021-08-27

Acknowledgements:

 - [Francisco Vallarino](https://github.com/fjvallarino) for [Haskell bindings for libmdbx](https://hackage.haskell.org/package/libmdbx).
 - [Alex Sharov](https://github.com/AskAlexSharov) for reporting and testing.
 - [Andrea Lanfranchi](https://github.com/AndreaLanfranchi) for contributing.

Extensions and improvements:

 - Added `cursor::erase()` overloads for `key` and for `key-value`.
 - Resolve minor Coverity Scan issues (no fixes but some hint/comment were added).
 - Resolve minor UndefinedBehaviorSanitizer issues (no fixes but some workaround were added).

Fixes:

 - Always setup `madvise` while opening DB (fixes https://github.com/erthink/libmdbx/issues/231).
 - Fixed checking legacy `P_DIRTY` flag (`0x10`) for nested/sub-pages.

Minors:

 - Fixed getting revision number from middle of history during amalgamation (GNU Makefile).
 - Fixed search GCC tools for LTO (CMake scripts).
 - Fixed/reorder dirs list for search CLANG tools for LTO (CMake scripts).
 - Fixed/workarounds for CLANG < 9.x
 - Fixed CMake warning about compatibility with 3.8.2


## v0.10.2 at 2021-07-26

Acknowledgements:

 - [Alex Sharov](https://github.com/AskAlexSharov) for reporting and testing.
 - [Andrea Lanfranchi](https://github.com/AndreaLanfranchi) for reporting bugs.
 - [Lionel Debroux](https://github.com/debrouxl) for fuzzing tests and reporting bugs.
 - [Sergey Fedotov](https://github.com/SergeyFromHell/) for [`node-mdbx` NodeJS bindings](https://www.npmjs.com/package/node-mdbx).
 - [Kris Zyp](https://github.com/kriszyp) for [`lmdbx-store` NodeJS bindings](https://github.com/kriszyp/lmdbx-store).
 - [Noel Kuntze](https://github.com/Thermi) for [draft Python bindings](https://github.com/erthink/libmdbx/commits/python-bindings).

New features, extensions and improvements:

 - [Allow to predefine/override `MDBX_BUILD_TIMESTAMP` for builds reproducibility](https://github.com/erthink/libmdbx/issues/201).
 - Added options support for `long-stochastic` script.
 - Avoided `MDBX_TXN_FULL` error for large transactions when possible.
 - The `MDBX_READERS_LIMIT` increased to `32767`.
 - Raise `MDBX_TOO_LARGE` under Valgrind/ASAN if being opened DB is 100 larger than RAM (to avoid hangs and OOM).
 - Minimized the size of poisoned/unpoisoned regions to avoid Valgrind/ASAN stuck.
 - Added more workarounds for QEMU for testing builds for 32-bit platforms, Alpha and Sparc architectures.
 - `mdbx_chk` now skips iteration & checking of DB' records if corresponding page-tree is corrupted (to avoid `SIGSEGV`, ASAN failures, etc).
 - Added more checks for [rare/fuzzing corruption cases](https://github.com/erthink/libmdbx/issues/217).

Backward compatibility break:

 - Use file `VERSION.txt` for version information instead of `VERSION` to avoid collision with `#include <version>`.
 - Rename `slice::from/to_FOO_bytes()` to `slice::envisage_from/to_FOO_length()'.
 - Rename `MDBX_TEST_EXTRA` make's variable to `MDBX_SMOKE_EXTRA`.
 - Some details of the C++ API have been changed for subsequent freezing.

Fixes:

 - Fixed excess meta-pages checks in case `mdbx_chk` is called to check the DB for a specific meta page and thus could prevent switching to the selected meta page, even if the check passed without errors.
 - Fixed [recursive use of SRW-lock on Windows cause by `MDBX_NOTLS` option](https://github.com/erthink/libmdbx/issues/203).
 - Fixed [log a warning during a new DB creation](https://github.com/erthink/libmdbx/issues/205).
 - Fixed [false-negative `mdbx_cursor_eof()` result](https://github.com/erthink/libmdbx/issues/207).
 - Fixed [`make install` with non-GNU `install` utility (OSX, BSD)](https://github.com/erthink/libmdbx/issues/208).
 - Fixed [installation by `CMake` in special cases by complete use `GNUInstallDirs`'s variables](https://github.com/erthink/libmdbx/issues/209).
 - Fixed [C++ Buffer issue with `std::string` and alignment](https://github.com/erthink/libmdbx/issues/191).
 - Fixed `safe64_reset()` for platforms without atomic 64-bit compare-and-swap.
 - Fixed hang/shutdown on big-endian platforms without `__cxa_thread_atexit()`.
 - Fixed [using bad meta-pages if DB was partially/recoverable corrupted](https://github.com/erthink/libmdbx/issues/217).
 - Fixed extra `noexcept` for `buffer::&assign_reference()`.
 - Fixed `bootid` generation on Windows for case of change system' time.
 - Fixed [test framework keygen-related issue](https://github.com/erthink/libmdbx/issues/127).


## v0.10.1 at 2021-06-01

Acknowledgements:

 - [Alexey Akhunov](https://github.com/AlexeyAkhunov) and [Alex Sharov](https://github.com/AskAlexSharov) for bug reporting and testing.
 - [Andrea Lanfranchi](https://github.com/AndreaLanfranchi) for bug reporting and testing related to WSL2.

New features:

 - Added `-p` option to `mdbx_stat` utility for printing page operations statistic.
 - Added explicit checking for and warning about using unfit github's archives.
 - Added fallback from [OFD locking](https://bit.ly/3yFRtYC) to legacy non-OFD POSIX file locks on an `EINVAL` error.
 - Added [Plan 9](https://en.wikipedia.org/wiki/9P_(protocol)) network file system to the whitelist for an ability to open a DB in exclusive mode.
 - Support for opening from WSL2 environment a DB hosted on Windows drive and mounted via [DrvFs](https://docs.microsoft.com/it-it/archive/blogs/wsl/wsl-file-system-support#drvfs) (i.e by Plan 9 noted above).

Fixes:

 - Fixed minor "foo not used" warnings from modern C++ compilers when building the C++ part of the library.
 - Fixed confusing/messy errors when build library from unfit github's archives (https://github.com/erthink/libmdbx/issues/197).
 - Fixed `#​e​l​s​i​f` typo.
 - Fixed rare unexpected `MDBX_PROBLEM` error during altering data in huge transactions due to wrong spilling/oust of dirty pages (https://github.com/erthink/libmdbx/issues/195).
 - Re-Fixed WSL1/WSL2 detection with distinguishing (https://github.com/erthink/libmdbx/issues/97).


## v0.10.0 at 2021-05-09

Acknowledgements:

 - [Mahlon E. Smith](https://github.com/mahlonsmith) for [Ruby bindings](https://rubygems.org/gems/mdbx/).
 - [Alex Sharov](https://github.com/AskAlexSharov) for [mdbx-go](https://github.com/torquem-ch/mdbx-go), bug reporting and testing.
 - [Artem Vorotnikov](https://github.com/vorot93) for bug reporting and PR.
 - [Paolo Rebuffo](https://www.linkedin.com/in/paolo-rebuffo-8255766/), [Alexey Akhunov](https://github.com/AlexeyAkhunov) and Mark Grosberg for donations.
 - [Noel Kuntze](https://github.com/Thermi) for preliminary [Python bindings](https://github.com/Thermi/libmdbx/tree/python-bindings)

New features:

 - Added `mdbx_env_set_option()` and `mdbx_env_get_option()` for controls
   various runtime options for an environment (announce of this feature  was missed in a previous news).
 - Added `MDBX_DISABLE_PAGECHECKS` build option to disable some checks to reduce an overhead
   and detection probability of database corruption to a values closer to the LMDB.
   The `MDBX_DISABLE_PAGECHECKS=1` provides a performance boost of about 10% in CRUD scenarios,
   and conjointly with the `MDBX_ENV_CHECKPID=0` and `MDBX_TXN_CHECKOWNER=0` options can yield
   up to 30% more performance compared to LMDB.
 - Using float point (exponential quantized) representation for internal 16-bit values
   of grow step and shrink threshold when huge ones (https://github.com/erthink/libmdbx/issues/166).
   To minimize the impact on compatibility, only the odd values inside the upper half
   of the range (i.e. 32769..65533) are used for the new representation.
 - Added the `mdbx_drop` similar to LMDB command-line tool to purge or delete (sub)database(s).
 - [Ruby bindings](https://rubygems.org/gems/mdbx/) is available now by [Mahlon E. Smith](https://github.com/mahlonsmith).
 - Added `MDBX_ENABLE_MADVISE` build option which controls the use of POSIX `madvise()` hints and friends.
 - The internal node sizes were refined, resulting in a reduction in large/overflow pages in some use cases
   and a slight increase in limits for a keys size to ≈½ of page size.
 - Added to `mdbx_chk` output number of keys/items on pages.
 - Added explicit `install-strip` and `install-no-strip` targets to the `Makefile` (https://github.com/erthink/libmdbx/pull/180).
 - Major rework page splitting (af9b7b560505684249b76730997f9e00614b8113) for
     - An "auto-appending" feature upon insertion for both ascending and
       descending key sequences. As a result, the optimality of page filling
       increases significantly (more densely, less slackness) while
       inserting ordered sequences of keys,
     - A "splitting at middle" to make page tree more balanced on average.
 - Added `mdbx_get_sysraminfo()` to the API.
 - Added guessing a reasonable maximum DB size for the default upper limit of geometry (https://github.com/erthink/libmdbx/issues/183).
 - Major rework internal labeling of a dirty pages (958fd5b9479f52f2124ab7e83c6b18b04b0e7dda) for
   a "transparent spilling" feature with the gist to make a dirty pages
   be ready to spilling (writing to a disk) without further altering ones.
   Thus in the `MDBX_WRITEMAP` mode the OS kernel able to oust dirty pages
   to DB file without further penalty during transaction commit.
   As a result, page swapping and I/O could be significantly reduced during extra large transactions and/or lack of memory.
 - Minimized reading leaf-pages during dropping subDB(s) and nested trees.
 - Major rework a spilling of dirty pages to support [LRU](https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU))
   policy and prioritization for a large/overflow pages.
 - Statistics of page operations (split, merge, copy, spill, etc) now available through `mdbx_env_info_ex()`.
 - Auto-setup limit for length of dirty pages list (`MDBX_opt_txn_dp_limit` option).
 - Support `make options` to list available build options.
 - Support `make help` to list available make targets.
 - Silently `make`'s build by default.
 - Preliminary [Python bindings](https://github.com/Thermi/libmdbx/tree/python-bindings) is available now
   by [Noel Kuntze](https://github.com/Thermi) (https://github.com/erthink/libmdbx/issues/147).

Backward compatibility break:

 - The `MDBX_AVOID_CRT` build option was renamed to `MDBX_WITHOUT_MSVC_CRT`.
   This option is only relevant when building for Windows.
 - The `mdbx_env_stat()` always, and `mdbx_env_stat_ex()` when called with the zeroed transaction parameter,
   now internally start temporary read transaction and thus may returns `MDBX_BAD_RSLOT` error.
   So, just never use deprecated `mdbx_env_stat()' and call `mdbx_env_stat_ex()` with transaction parameter.
 - The build option `MDBX_CONFIG_MANUAL_TLS_CALLBACK` was removed and now just a non-zero value of
   the `MDBX_MANUAL_MODULE_HANDLER` macro indicates the requirement to manually call `mdbx_module_handler()`
   when loading libraries and applications uses statically linked libmdbx on an obsolete Windows versions.

Fixes:

 - Fixed performance regression due non-optimal C11 atomics usage (https://github.com/erthink/libmdbx/issues/160).
 - Fixed "reincarnation" of subDB after it deletion (https://github.com/erthink/libmdbx/issues/168).
 - Fixed (disallowing) implicit subDB deletion via operations on `@MAIN`'s DBI-handle.
 - Fixed a crash of `mdbx_env_info_ex()` in case of a call for a non-open environment (https://github.com/erthink/libmdbx/issues/171).
 - Fixed the selecting/adjustment values inside `mdbx_env_set_geometry()` for implicit out-of-range cases (https://github.com/erthink/libmdbx/issues/170).
 - Fixed `mdbx_env_set_option()` for set initial and limit size of dirty page list ((https://github.com/erthink/libmdbx/issues/179).
 - Fixed an unreasonably huge default upper limit for DB geometry (https://github.com/erthink/libmdbx/issues/183).
 - Fixed `constexpr` specifier for the `slice::invalid()`.
 - Fixed (no)readahead auto-handling (https://github.com/erthink/libmdbx/issues/164).
 - Fixed non-alloy build for Windows.
 - Switched to using Heap-functions instead of LocalAlloc/LocalFree on Windows.
 - Fixed `mdbx_env_stat_ex()` to returning statistics of the whole environment instead of MainDB only (https://github.com/erthink/libmdbx/issues/190).
 - Fixed building by GCC 4.8.5 (added workaround for a preprocessor's bug).
 - Fixed building C++ part for iOS <= 13.0 (unavailability of  `std::filesystem::path`).
 - Fixed building for Windows target versions prior to Windows Vista (`WIN32_WINNT < 0x0600`).
 - Fixed building by MinGW for Windows (https://github.com/erthink/libmdbx/issues/155).


## v0.9.3 at 2021-02-02

Acknowledgements:

 - [Mahlon E. Smith](http://www.martini.nu/) for [FreeBSD port of libmdbx](https://svnweb.freebsd.org/ports/head/databases/mdbx/).
 - [장세연](http://www.castis.com) for bug fixing and PR.
 - [Clément Renault](https://github.com/Kerollmops/heed) for [Heed](https://github.com/Kerollmops/heed) fully typed Rust wrapper.
 - [Alex Sharov](https://github.com/AskAlexSharov) for bug reporting.
 - [Noel Kuntze](https://github.com/Thermi) for bug reporting.

Removed options and features:

 - Drop `MDBX_HUGE_TRANSACTIONS` build-option (now no longer required).

New features:

 - Package for FreeBSD is available now by Mahlon E. Smith.
 - New API functions to get/set various options (https://github.com/erthink/libmdbx/issues/128):
    - the maximum number of named databases for the environment;
    - the maximum number of threads/reader slots;
    - threshold (since the last unsteady commit) to force flush the data buffers to disk;
    - relative period (since the last unsteady commit) to force flush the data buffers to disk;
    - limit to grow a list of reclaimed/recycled page's numbers for finding a sequence of contiguous pages for large data items;
    - limit to grow a cache of dirty pages for reuse in the current transaction;
    - limit of a pre-allocated memory items for dirty pages;
    - limit of dirty pages for a write transaction;
    - initial allocation size for dirty pages list of a write transaction;
    - maximal part of the dirty pages may be spilled when necessary;
    - minimal part of the dirty pages should be spilled when necessary;
    - how much of the parent transaction dirty pages will be spilled while start each child transaction;
 - Unlimited/Dynamic size of retired and dirty page lists (https://github.com/erthink/libmdbx/issues/123).
 - Added `-p` option (purge subDB before loading) to `mdbx_load` tool.
 - Reworked spilling of large transaction and committing of nested transactions:
    - page spilling code reworked to avoid the flaws and bugs inherited from LMDB;
    - limit for number of dirty pages now is controllable at runtime;
    - a spilled pages, including overflow/large pages, now can be reused and refunded/compactified in nested transactions;
    - more effective refunding/compactification especially for the loosed page cache.
 - Added `MDBX_ENABLE_REFUND` and `MDBX_PNL_ASCENDING` internal/advanced build options.
 - Added `mdbx_default_pagesize()` function.
 - Better support architectures with a weak/relaxed memory consistency model (ARM, AARCH64, PPC, MIPS, RISC-V, etc) by means [C11 atomics](https://en.cppreference.com/w/c/atomic).
 - Speed up page number lists and dirty page lists (https://github.com/erthink/libmdbx/issues/132).
 - Added `LIBMDBX_NO_EXPORTS_LEGACY_API` build option.

Fixes:

 - Fixed missing cleanup (null assigned) in the C++ commit/abort (https://github.com/erthink/libmdbx/pull/143).
 - Fixed `mdbx_realloc()` for case of nullptr and `MDBX_WITHOUT_MSVC_CRT=ON` for Windows.
 - Fixed the possibility to use invalid and renewed (closed & re-opened, dropped & re-created) DBI-handles (https://github.com/erthink/libmdbx/issues/146).
 - Fixed 4-byte aligned access to 64-bit integers, including access to the `bootid` meta-page's field (https://github.com/erthink/libmdbx/issues/153).
 - Fixed minor/potential memory leak during page flushing and unspilling.
 - Fixed handling states of cursors's and subDBs's for nested transactions.
 - Fixed page leak in extra rare case the list of retired pages changed during update GC on transaction commit.
 - Fixed assertions to avoid false-positive UB detection by CLANG/LLVM (https://github.com/erthink/libmdbx/issues/153).
 - Fixed `MDBX_TXN_FULL` and regressive `MDBX_KEYEXIST` during large transaction commit with `MDBX_LIFORECLAIM` (https://github.com/erthink/libmdbx/issues/123).
 - Fixed auto-recovery (`weak->steady` with the same boot-id) when Database size at last weak checkpoint is large than at last steady checkpoint.
 - Fixed operation on systems with unusual small/large page size, including PowerPC (https://github.com/erthink/libmdbx/issues/157).


## v0.9.2 at 2020-11-27

Acknowledgements:

 - Jens Alfke (Mobile Architect at [Couchbase](https://www.couchbase.com/)) for [NimDBX](https://github.com/snej/nimdbx).
 - Clément Renault (CTO at [MeiliSearch](https://www.meilisearch.com/)) for [mdbx-rs](https://github.com/Kerollmops/mdbx-rs).
 - Alex Sharov (Go-Lang Teach Lead at [TurboGeth/Ethereum](https://ethereum.org/)) for an extreme test cases and bug reporting.
 - George Hazan (CTO at [Miranda NG](https://www.miranda-ng.org/)) for bug reporting.
 - [Positive Technologies](https://www.ptsecurity.com/) for funding and [The Standoff](https://standoff365.com/).

Added features:

 - Provided package for [buildroot](https://buildroot.org/).
 - Binding for Nim is [available](https://github.com/snej/nimdbx) now by Jens Alfke.
 - Added `mdbx_env_delete()` for deletion an environment files in a proper and multiprocess-safe way.
 - Added `mdbx_txn_commit_ex()` with collecting latency information.
 - Fast completion pure nested transactions.
 - Added `LIBMDBX_INLINE_API` macro and inline versions of some API functions.
 - Added `mdbx_cursor_copy()` function.
 - Extended tests for checking cursor tracking.
 - Added `MDBX_SET_LOWERBOUND` operation for `mdbx_cursor_get()`.

Fixes:

 - Fixed missing installation of `mdbx.h++`.
 - Fixed use of obsolete `__noreturn`.
 - Fixed use of `yield` instruction on ARM if unsupported.
 - Added pthread workaround for buggy toolchain/cmake/buildroot.
 - Fixed use of `pthread_yield()` for non-GLIBC.
 - Fixed use of `RegGetValueA()` on Windows 2000/XP.
 - Fixed use of `GetTickCount64()` on Windows 2000/XP.
 - Fixed opening DB on a network shares (in the exclusive mode).
 - Fixed copy&paste typos.
 - Fixed minor false-positive GCC warning.
 - Added workaround for broken `DEFINE_ENUM_FLAG_OPERATORS` from Windows SDK.
 - Fixed cursor state after multimap/dupsort repeated deletes (https://github.com/erthink/libmdbx/issues/121).
 - Added `SIGPIPE` suppression for internal thread during `mdbx_env_copy()`.
 - Fixed extra-rare `MDBX_KEY_EXIST` error during `mdbx_commit()` (https://github.com/erthink/libmdbx/issues/131).
 - Fixed spilled pages checking (https://github.com/erthink/libmdbx/issues/126).
 - Fixed `mdbx_load` for 'plain text' and without `-s name` cases (https://github.com/erthink/libmdbx/issues/136).
 - Fixed save/restore/commit of cursors for nested transactions.
 - Fixed cursors state in rare/special cases (move next beyond end-of-data, after deletion and so on).
 - Added workaround for MSVC 19.28 (Visual Studio 16.8) (but may still hang during compilation).
 - Fixed paranoidal Clang C++ UB for bitwise operations with flags defined by enums.
 - Fixed large pages checking (for compatibility and to avoid false-positive errors from `mdbx_chk`).
 - Added workaround for Wine (https://github.com/miranda-ng/miranda-ng/issues/1209).
 - Fixed `ERROR_NOT_SUPPORTED` while opening DB by UNC pathnames (https://github.com/miranda-ng/miranda-ng/issues/2627).
 - Added handling `EXCEPTION_POSSIBLE_DEADLOCK` condition for Windows.


## v0.9.1 2020-09-30

Added features:

 - Preliminary C++ API with support for C++17 polymorphic allocators.
 - [Online C++ API reference](https://erthink.github.io/libmdbx/) by Doxygen.
 - Quick reference for Insert/Update/Delete operations.
 - Explicit `MDBX_SYNC_DURABLE` to sync modes for API clarity.
 - Explicit `MDBX_ALLDUPS` and `MDBX_UPSERT` for API clarity.
 - Support for read transactions preparation (`MDBX_TXN_RDONLY_PREPARE` flag).
 - Support for cursor preparation/(pre)allocation and reusing (`mdbx_cursor_create()` and `mdbx_cursor_bind()` functions).
 - Support for checking database using specified meta-page (see `mdbx_chk -h`).
 - Support for turn to the specific meta-page after checking (see `mdbx_chk -h`).
 - Support for explicit reader threads (de)registration.
 - The `mdbx_txn_break()` function to explicitly mark a transaction as broken.
 - Improved handling of corrupted databases by `mdbx_chk` utility and `mdbx_walk_tree()` function.
 - Improved DB corruption detection by checking parent-page-txnid.
 - Improved opening large DB (> 4Gb) from 32-bit code.
 - Provided `pure-function` and `const-function` attributes to C API.
 - Support for user-settable context for transactions & cursors.
 - Revised API and documentation related to Handle-Slow-Readers callback feature.

Deprecated functions and flags:

 - For clarity and API simplification the `MDBX_MAPASYNC` flag is deprecated.
   Just use `MDBX_SAFE_NOSYNC` or `MDBX_UTTERLY_NOSYNC` instead of it.
 - `MDBX_oom_func`, `mdbx_env_set_oomfunc()` and `mdbx_env_get_oomfunc()`
   replaced with `MDBX_hsr_func`, `mdbx_env_get_hsr` and `mdbx_env_get_hsr()`.

Fixes:

 - Fix `mdbx_strerror()` for `MDBX_BUSY` error (no error description is returned).
 - Fix update internal meta-geo information in read-only mode (`EACCESS` or `EBADFD` error).
 - Fix `mdbx_page_get()` null-defer when DB corrupted (crash by `SIGSEGV`).
 - Fix `mdbx_env_open()` for re-opening after non-fatal errors (`mdbx_chk` unexpected failures).
 - Workaround for MSVC 19.27 `static_assert()` bug.
 - Doxygen descriptions and refinement.
 - Update Valgrind's suppressions.
 - Workaround to avoid infinite loop of 'nested' testcase on MIPS under QEMU.
 - Fix a lot of typos & spelling (Thanks to Josh Soref for PR).
 - Fix `getopt()` messages for Windows (Thanks to Andrey Sporaw for reporting).
 - Fix MSVC compiler version requirements (Thanks to Andrey Sporaw for reporting).
 - Workarounds for QEMU's bugs to run tests for cross-builded library under QEMU.
 - Now C++ compiler optional for building by CMake.


## v0.9.0 2020-07-31 (not a release, but API changes)

Added features:

 - [Online C API reference](https://erthink.github.io/libmdbx/) by Doxygen.
 - Separated enums for environment, sub-databases, transactions, copying and data-update flags.

Deprecated functions and flags:

 - Usage of custom comparators and the `mdbx_dbi_open_ex()` are deprecated, since such databases couldn't be checked by the `mdbx_chk` utility.
   Please use the value-to-key functions to provide keys that are compatible with the built-in libmdbx comparators.


## v0.8.2 2020-07-06
- Added support multi-opening the same DB in a process with SysV locking (BSD).
- Fixed warnings & minors for LCC compiler (E2K).
- Enabled to simultaneously open the same database from processes with and without the `MDBX_WRITEMAP` option.
- Added key-to-value, `mdbx_get_keycmp()` and `mdbx_get_datacmp()` functions (helpful to avoid using custom comparators).
- Added `ENABLE_UBSAN` CMake option to enabling the UndefinedBehaviorSanitizer from GCC/CLANG.
- Workaround for [CLANG bug](https://bugs.llvm.org/show_bug.cgi?id=43275).
- Returning `MDBX_CORRUPTED` in case all meta-pages are weak and no other error.
- Refined mode bits while auto-creating LCK-file.
- Avoids unnecessary database file re-mapping in case geometry changed by another process(es).
  From the user's point of view, the `MDBX_UNABLE_EXTEND_MAPSIZE` error will now be returned less frequently and only when using the DB in the current process really requires it to be reopened.
- Remapping on-the-fly and of the database file was implemented.
  Now remapping with a change of address is performed automatically if there are no dependent readers in the current process.


## v0.8.1 2020-06-12
- Minor change versioning. The last number in the version now means the number of commits since last release/tag.
- Provide ChangeLog file.
- Fix for using libmdbx as a C-only sub-project with CMake.
- Fix `mdbx_env_set_geometry()` for case it is called from an opened environment outside of a write transaction.
- Add support for huge transactions and `MDBX_HUGE_TRANSACTIONS` build-option (default `OFF`).
- Refine LTO (link time optimization) for clang.
- Force enabling exceptions handling for MSVC (`/EHsc` option).


## v0.8.0 2020-06-05
- Support for Android/Bionic.
- Support for iOS.
- Auto-handling `MDBX_NOSUBDIR` while opening for any existing database.
- Engage github-actions to make release-assets.
- Clarify API description.
- Extended keygen-cases in stochastic test.
- Fix fetching of first/lower key from LEAF2-page during page merge.
- Fix missing comma in array of error messages.
- Fix div-by-zero while copy-with-compaction for non-resizable environments.
- Fixes & enhancements for custom-comparators.
- Fix `MDBX_WITHOUT_MSVC_CRT` option and missing `ntdll.def`.
- Fix `mdbx_env_close()` to work correctly called concurrently from several threads.
- Fix null-deref in an ASAN-enabled builds while opening the environment with error and/or read-only.
- Fix AddressSanitizer errors after closing the environment.
- Fix/workaround to avoid GCC 10.x pedantic warnings.
- Fix using `ENODATA` for FreeBSD.
- Avoid invalidation of DBI-handle(s) when it just closes.
- Avoid using `pwritev()` for single-writes (up to 10% speedup for some kernels & scenarios).
- Avoiding `MDBX_UTTERLY_NOSYNC` as result of flags merge.
- Add `mdbx_dbi_dupsort_depthmask()` function.
- Add `MDBX_CP_FORCE_RESIZEABLE` option.
- Add deprecated `MDBX_MAP_RESIZED` for compatibility.
- Add `MDBX_BUILD_TOOLS` option (default `ON`).
- Refine `mdbx_dbi_open_ex()` to safe concurrently opening the same handle from different threads.
- Truncate clk-file during environment closing. So a zero-length lck-file indicates that the environment was closed properly.
- Refine `mdbx_update_gc()` for huge transactions with small sizes of database page.
- Extends dump/load to support all MDBX attributes.
- Avoid upsertion the same key-value data, fix related assertions.
- Rework min/max length checking for keys & values.
- Checking the order of keys on all pages during checking.
- Support `CFLAGS_EXTRA` make-option for convenience.
- Preserve the last txnid while copying with compactification.
- Auto-reset running transaction in mdbx_txn_renew().
- Automatically abort errored transaction in mdbx_txn_commit().
- Auto-choose page size for large databases.
- Rearrange source files, rework build, options-support by CMake.
- Crutch for WSL1 (Windows subsystem for Linux).
- Refine install/uninstall targets.
- Support for Valgrind 3.14 and later.
- Add check-analyzer check-ubsan check-asan check-leak targets to Makefile.
- Minor fix/workaround to avoid UBSAN traps for `memcpy(ptr, NULL, 0)`.
- Avoid some GCC-analyzer false-positive warnings.


## v0.7.0 2020-03-18
- Workarounds for Wine (Windows compatibility layer for Linux).
- `MDBX_MAP_RESIZED` renamed to `MDBX_UNABLE_EXTEND_MAPSIZE`.
- Clarify API description, fix typos.
- Speedup runtime checks in debug/checked builds.
- Added checking for read/write transactions overlapping for the same thread, added `MDBX_TXN_OVERLAPPING` error and `MDBX_DBG_LEGACY_OVERLAP` option.
- Added `mdbx_key_from_jsonInteger()`, `mdbx_key_from_double()`, `mdbx_key_from_float()`, `mdbx_key_from_int64()` and `mdbx_key_from_int32()` functions. See `mdbx.h` for description.
- Fix compatibility (use zero for invalid DBI).
- Refine/clarify error messages.
- Avoids extra error messages "bad txn" from mdbx_chk when DB is corrupted.


## v0.6.0 2020-01-21
- Fix `mdbx_load` utility for custom comparators.
- Fix checks related to `MDBX_APPEND` flag inside `mdbx_cursor_put()`.
- Refine/fix dbi_bind() internals.
- Refine/fix handling `STATUS_CONFLICTING_ADDRESSES`.
- Rework `MDBX_DBG_DUMP` option to avoid disk I/O performance degradation.
- Add built-in help to test tool.
- Fix `mdbx_env_set_geometry()` for large page size.
- Fix env_set_geometry() for large pagesize.
- Clarify API description & comments, fix typos.


## v0.5.0 2019-12-31
- Fix returning MDBX_RESULT_TRUE from page_alloc().
- Fix false-positive ASAN issue.
- Fix assertion for `MDBX_NOTLS` option.
- Rework `MADV_DONTNEED` threshold.
- Fix `mdbx_chk` utility for don't checking some numbers if walking on the B-tree was disabled.
- Use page's mp_txnid for basic integrity checking.
- Add `MDBX_FORCE_ASSERTIONS` built-time option.
- Rework `MDBX_DBG_DUMP` to avoid performance degradation.
- Rename `MDBX_NOSYNC` to `MDBX_SAFE_NOSYNC` for clarity.
- Interpret `ERROR_ACCESS_DENIED` from `OpenProcess()` as 'process exists'.
- Avoid using `FILE_FLAG_NO_BUFFERING` for compatibility with small database pages.
- Added install section for CMake.


## v0.4.0 2019-12-02
- Support for Mac OSX, FreeBSD, NetBSD, OpenBSD, DragonFly BSD, OpenSolaris, OpenIndiana (AIX and HP-UX pending).
- Use bootid for decisions of rollback.
- Counting retired pages and extended transaction info.
- Add `MDBX_ACCEDE` flag for database opening.
- Using OFD-locks and tracking for in-process multi-opening.
- Hot backup into pipe.
- Support for cmake & amalgamated sources.
- Fastest internal sort implementation.
- New internal dirty-list implementation with lazy sorting.
- Support for lazy-sync-to-disk with polling.
- Extended key length.
- Last update transaction number for each sub-database.
- Automatic read ahead enabling/disabling.
- More auto-compactification.
- Using -fsanitize=undefined and -Wpedantic options.
- Rework page merging.
- Nested transactions.
- API description.
- Checking for non-local filesystems to avoid DB corruption.