remove file RW mutex, replace it by more granular bucket RW mutex
hash bucket mutex performance improvement
fix benchmark2 array size being 1000 less
totally remove file lock, replaced them by more granular locks
remove per-document lock, it does not help improving performance
remove unnecessary rlocks from col.ForAll
Revert "remove unnecessary rlocks from col.ForAll"

This reverts commit feb3940c8b4f25a058001520e4cdfaad8b1ed350.
Revert "remove per-document lock, it does not help improving performance"

This reverts commit 0593cff5db087c1f9296c8219b65eeb053d79b8c.
implement concurrent access to document and hash table locks