In the WiredTigerRecordStore we keep track of the number of records we hold. When a transaction rollbacks we patch up the metadata so that eventually it stays in sync with the real number of rows, even though it can get out of sync if there's a crash.

To fix up issues after a crash, we clamp the value to a positive integer however this can cause problems if there are rollbacks:

• Thread 1 deletes the last row, sets numRecords = 0
• Thread 1 rollbacks, it rollbacks the WT transaction but hasn't fixed up the metadata yet
• Thread 2 deletes the last row, numRecords is 0 so it clamps numRecords to 0 and commits.
• Thread 1 fixes up the metadata by increasing numRecords by the same amount it reduced, numRecords = 1

We should allow negative values of numRecords so that the metadata patching process works correctly.