Javadoc
A auxiliary object to keep the size slot for a
DomainBPlusTreeJVSTM.
To avoid write conflicts, the writing to this slot is done with the help of PerTxBoxes.
This delays the read of the size box until after the transaction validation.
Thus, two transactions can add elements to different LeafNodes of the same tree.
Although these transactions will both increment the same size slot, they will not conflict.
This auxiliary object is necessary, because of the one-box layout used in the JVSTM+OJB backend.
If the size slot was declared directly in the
DomainBPlusTreeJVSTM, the read of the box
would occur as soon as a transaction would get the root node to insert/remove elements.