OP_WILDCARD with multidb

[Olly Betts]

Currently the limits for both of these are applied separately for each subdatabase in the multidatabase case - really they should both work the same as for a single database containing the same documents as all the subdatabases.

OP_ELITE_SET and QueryParser's wildcard expansion limits do work that way in 1.2.x, so this seems like it ought to be fixed before 1.4.0.

[Olly Betts]

Turns out OP_ELITE_SET is easy to fix - we just remove the special case check for termfreq_max() being zero! That's done in [6f3ff69b87bf50390c09c4f0f31740857c241109].

The fix for OP_WILDCARD is unfortunately not just a matter of deleting a couple of lines of code.

The reason for the wildcard limits is to improve performance so we want the implementation to be efficient, and perhaps that's more important than it being exact. Care is certainly needed to make sure any fix isn't a lot slower.

As I noted in the description, 1,2's QueryParser wildcard expansion limits work differently, but the current behaviour isn't entirely unreasonable, and OP_WILDCARD and these limits are new features.

So I think for 1.4.0 we document what currently happens, and note that these details may change - done in [a6cbcf9ee8c091adef1547571ac502f8c78343c2].

[Olly Betts]

A related problem is that we currently use the shard's termfreqs for weighting: [b0834cbac83d2cc02faa1fe0fbb03a8e6f6684f5]