Libmdbx

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).

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).

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.

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.

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.

- 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.