This commit adds the ability to start a transaction with an exclusive
lock for the entire database. This ensures no other read or write
transactions can run at the same time. Writes in this mode write
directly to the database and skip the WAL entirely.
Previously, the `rbf.DB.opened` flag was set after `checkpoint()`
when reopening, however, this flag is checked by `checkpoint()` so
it was not properly executing.
- rbf had races around the new rootRecords cache in tx
- rbf tx needed a write lock on the db now that rootRecords are written
- added a global registry for rbfDB to correctly dedup instances
- implement DeleteFragment, DeleteIndex for rbf
- use badger style keys for rbf to allow content checksumming to be list
containers in the same order
- lots of other integration of rbf into pilosa layer.
Previously, the `checkpoint()` function determined the segments to drop
based on the current active transactions' WAL ID references. However, if
no transactions are active then the checkpoint would drop segments too
aggressively.
This changes the determination by using the highest WAL ID that is
actually checkpointed to disk to determine the high water mark. If no
page are checkpointed then no segments can be dropped.
a) All tests green under -race for both PILOSA_TXSRC=roaring and PILOSA_TXSRC=badger.
b) Distinct is merged back into mainline pilosa.
Seebs notes on the Distinct work:
merge Distinct plugin back into main source tree, convert to Tx
We drop all references to the Preemptively Deprecated Don't You Dare
Use This extension interface, and move the one and only extension we had
(Distinct) into the main executor.
Also this fixes an arguable bug, which is that Container.AsBitmap()
would panic on a nil parameter, but it should have returned an empty
bitmap, because a nil *Ccontainer is a valid empty container. This
simplifies logic significantly in Distinct.
Fixes#569#570#571#572#573#584#585
