LevelDB update to v1.22

[braydonf]

No description provided.

[braydonf]

I think we can hold off on this update until later, however I'll leave this open as example on what is necessary to upgrade, when ready.

[tynes]

I didn't realize that you had an open PR for this @braydonf

I think this is more important after seeing a bug in v1.20 about keys being lost during compaction.
See google/leveldb#339

This is a good precursor to make sure that it still builds on Windows #11

See my branch here:
https://github.com/tynes/bdb/tree/leveldb-1.22

[braydonf]

I was about to reply in the other thread. Yeah I started this when investigating segmentation fault issues (with the bindings) that have since been fixed. Leveldown (upstream) still hasn't upgraded, however Bitcoin Core has as part of the latest release candidate.

[tynes]

I have a logfile of a bcoin sync with LevelDB 1.20 and another with 1.22, I'd like to dig into them to see if there were any major differences. I also think it would be straightforward to write a benchmark that indexes and reads a bunch of data in a deterministic way to see if there are performance differences.

Once I have it building on Windows (thanks for the merge here #11), I'll revisit this PR. I feel a lot more comfortable upgrading to 1.22 if Bitcoin Core is also planning on doing so.