Add a quad to the pending-adds queue
Add a quad to the pending-deletes queue
Flush all pending operations to IndexedDB in a single readwrite transaction.
The transaction covers both "terms" and all three index stores so that dictionary entries and index entries are always written atomically.
If a flush is already in progress, we wait for it to complete and then run again (to pick up any operations queued during the first flush).
Returns a snapshot of pending adds (does not drain the buffer)
Returns a snapshot of pending deletes (does not drain the buffer)
Stop the auto-flush timer (call before closing the database)
Total number of operations waiting to be flushed