The reblock-ovf command forces contiguous overflow blocks that exist in different internal tables to be compared and combined if possible.
The overflow is split into a safe table, which contains the largest available blocks, and the normal B-tree table which contains smaller blocks. After a crash, the safe table is used to recover the overflow to a known state. Because of this separation, it is sometimes possible to have blocks which appear to be numerically contiguous, but which are not combined because they exist in different tables. The reblock-ovf command corrects this situation.