database: investigate replacing leveldb with pebble

[Roasbeef]

database: investigate replacing leveldb with pebble

[kcalvinalvin]

FWIW leveldb itself hasn't had that much development either. I don't think it necessarily means lack of maintenance.

That being said, I'm not opposed to having pebble as an option. If it ends up being more performant, that's a win. Though maybe have a big warning that pebble itself may not be consensus compatible with leveldb.

[0xEclair]

If no enough performance improvement, i think there is no need to replace leveldb with pebble. To replace, we must do a lot of test for pebble to check whether there are internal bugs like missing data or incorrect values when insert or get.

Another point, maybe keepping building pebble means that there are bugs. leveldb is enough stable and safe.