Looking at these two lines of source in WT and MMapV1:
Note that in WT a '>' is used and in MMapV1 a '>=' is used. Given a capped collection of size 100, if we insert two documents of size 50 and then truncation occurs:
- in MMapV1, one document will get deleted because its position would be >= 100
- in WT no documents would be deleted because the size would not be > 100.
These two behaviors should be made the same, likely in favor of the existing MMapV1 behavior.