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std::string shouldn't be used inside mdbx::buffer #191

erthink opened this issue May 4, 2021 · 3 comments

std::string shouldn't be used inside mdbx::buffer #191

erthink opened this issue May 4, 2021 · 3 comments


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@erthink erthink commented May 4, 2021


Lines 807 to 813 in 7d54518

/* FIXME: replace std::string with custom silo.
* The std::string<char> does not guarantee any alignment for allocated
* buffer. For instance short values may be stored within internal inplace
* buffer, which might odd address. Moreover, allocator for the `char` type
* may return unaligned/odd address. This may UB for placing a 32-bit and
* 64-bit values.
* So seems the std::string<> should be replaced with ad hoc solution. */

@erthink erthink added the bug label May 4, 2021
@erthink erthink self-assigned this May 4, 2021
erthink added a commit that referenced this issue May 9, 2021
 - [Mahlon E. Smith]( for [Ruby bindings](
 - [Alex Sharov]( for [mdbx-go](, bug reporting and testing.
 - [Artem Vorotnikov]( for bug reporting and PR.
 - [Paolo Rebuffo](, [Alexey Akhunov]( and Mark Grosberg for donations.
 - [Noel Kuntze]( for preliminary [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 (#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]( is available now by [Mahlon E. Smith](
 - 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` (#180).
 - Major rework page splitting (af9b7b5) 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 (#183).
 - Major rework internal labeling of a dirty pages (958fd5b) 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](
   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]( is available now
   by [Noel Kuntze]( (#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.

 - Fixed performance regression due non-optimal C11 atomics usage (#160).
 - Fixed "reincarnation" of subDB after it deletion (#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 (#171).
 - Fixed the selecting/adjustment values inside `mdbx_env_set_geometry()` for implicit out-of-range cases (#170).
 - Fixed `mdbx_env_set_option()` for set initial and limit size of dirty page list ((#179).
 - Fixed an unreasonably huge default upper limit for DB geometry (#183).
 - Fixed `constexpr` specifier for the `slice::invalid()`.
 - Fixed (no)readahead auto-handling (#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 (#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 (#155).

TODO for a next releases:
 - [Get rid of dirty-pages list in MDBX_WRITEMAP mode](#193).
 - [Large/Overflow pages accounting for dirty-room](#192).
 - [C++ Buffer issue](#191).
 - Finalize C++ API (few typos and trivia bugs are still likely for now).
 - [Support for RAW devices](#124).
 - [Test framework issue](#127).
 - [Support MessagePack for Keys & Values](#115).
 - [Engage new terminology](#137).
 - Packages for [Astra Linux](, [ALT Linux](, [ROSA Linux](, Fedora/RHEL, Debian/Ubuntu.
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@erthink erthink commented May 31, 2021

This affects the alignment of a buffer(s) with the CLANG's C++ standard library.

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@erthink erthink commented Jul 10, 2021

Fixed in the devel branch by bd2bb51.

erthink added a commit that referenced this issue Jul 26, 2021
 - [Alex Sharov]( for reporting and testing.
 - [Andrea Lanfranchi]( for reporting bugs.
 - [Lionel Debroux]( for fuzzing tests and reporting bugs.
 - [Sergey Fedotov]( for [`node-mdbx` NodeJS bindings](
 - [Kris Zyp]( for [`lmdbx-store` NodeJS bindings](
 - [Noel Kuntze]( for [draft Python bindings](

New features, extensions and improvements:
 - [Allow to predefine/override `MDBX_BUILD_TIMESTAMP` for builds reproducibility](#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](#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.

 - 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](#203).
 - Fixed [log a warning during a new DB creation](#205).
 - Fixed [false-negative `mdbx_cursor_eof()` result](#207).
 - Fixed [`make install` with non-GNU `install` utility (OSX, BSD)](#208).
 - Fixed [installation by `CMake` in special cases by complete use `GNUInstallDirs`'s variables](#209).
 - Fixed [C++ Buffer issue with `std::string` and alignment](#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](#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](#127).
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@erthink erthink commented Jul 26, 2021

Fixed now in the master branch and v0.10.2.

@erthink erthink closed this Jul 26, 2021
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