lmdb: limited support for mdb_set_compare and mdb_set_dupsort

[bmatsuo]

lmdb: limited support for mdb_set_compare and mdb_set_dupsort

[tbg]

Hi Bryan,

was just poking around the source code for exactly this, glad you've already given it a look.
Would you recommend I give the above a try using your feature branch? I'm not in any type of serious setting (so danger zone is fine as long as it has a chance of working).

cc cockroachdb/cockroach#5220

ps: I'm happy writing the comparator in C. In fact, it's already (mostly) there.

[bmatsuo]

You are welcome to try development against the branch I mentioned in the issue description. It may not always be up to date with master. But it's unlikely to have conflicts so merging master on your own is probably easy and safe enough. Feel free to comment on this branch (edit: thread) if anything like that comes up.

I haven't really been working hard toward this as I don't have a direct use case. But it sounds like you do. I would appreciate any help and feedback you can provide to help get this functionality merged.

There isn't any real solid documentation or good example at the moment. So working with the feature branch may be tricky right now. I'm still not sure how to set things up as cleanly as possible. But writing the comparison function in C should be the easiest thing to do. Additionally, it seems like it's simplest to define the function in a .c/.h file instead of the cgo header comment. But I think you can get things to work either way with some finesse.