mmapstorage

[mpranj]

Purpose

Introducing the mmapstorage plugin.

A simple storage plugin benchmark is added to compare it to dump. Many storage plugin tests were added to ctest. It does not yet store the OPMPHM data structure, but is compatible when OPMPHM is enabled. Two variants are compiled: mmapstorage, and mmapstorage_crc if zlib is available. The latter enables CRC32 checksum for the critical data (pointers, sizes, ...).

This is not the global cache plugin.

To enable it with cmake one can use -DKDB_DEFAULT_STORAGE=mmapstorage -DKDB_DB_FILE='default.mmap' -DKDB_DB_INIT='elektra.mmap'.

Checklist

• commit messages are fine ("module: short statement" syntax and refer to issues)
• I added unit tests
• I ran all tests locally and everything went fine
• affected documentation is fixed
• I added code comments, logging, and assertions (see doc/CODING.md)
• meta data is updated (e.g. README.md of plugins)
• release notes are updated (doc/news/_preparation_next_release.md)
• Add flag for CRC checksum in metadata.
• I added myself to AUTHORS

[mpranj]

@ingwinlu could you glance over 67ceb69 and see whether that would be the proper way to add a new build job with a different default storage plugin. I basically copied it from the ini job, but just want to make sure that is how you would do it.

[ingwinlu]

@mpranj lgtm

[mpranj]

Thanks, and thanks for putting all the hard work into the build system!

[mpranj]

@markus2330 other than the README, no major rewrites of the plugin are planned. The benchmarks will be improved, and a few tests might be added.

I plan to review everything again myself before I mark it as ready. If you want to do a preliminary review of the plugin code, it would make sense for me now.

NB: The checks haven't completed, but if something is broken it is nothing of major concern. Locally everything runs fine.

[markus2330]

It is better if you finish it first! Without a README.md reviewing is difficult.

[mpranj]

Thank you for the thorough review! I made the requested changes.
Additionally the following was done:

• added magic data / consistency checks for MmapMetaData (I overlooked this earlier)
• improved the output format (now CSV with header) of the storage benchmark for easier evaluation
• added the benchmark results to the news (but not into the plugin README). If you have a better idea how/where to put it, do tell.
• added myself to the AUTHORS file

If you have further change requests, please tell. Otherwise it can be merged.

[markus2330]

Thank you! A pleasure to merge such great code.