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.
Signed-off-by: Leonid Yuriev <leo@yuriev.ru>
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.
Signed-off-by: Leonid Yuriev <leo@yuriev.ru>
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.
