Extension for read-committed

[SeKwonLee]

The reference implementations of RECIPE indexes including P-CLHT, P-Bwtree, P-HOT, and P-ART have been updated to guarantee some read-related operations (range scan, negative lookup, and check for value existence) always return committed results by using a non-temporal store, PSwCAS (Persistent Single-word Compare And Swap), and simply adding additional flushes after some loads. Please check out the details about the updates to each index.

1. P-CLHT

• Final commit stores (setting or unsetting key entries) have been changed to employ non-temporal stores.

2. P-Bwtree

• Flushes are added after specific loads to the entries in the global mapping table. The specific loads include load instructions to the entries of the global mapping table pointing to the final leaf nodes where the resulting values are returned. The loads unrelated to the final leaf nodes don't have to call flushes such as the loads related to tree traversals.

3. P-HOT

• Final commit stores (swapping the parent pointer after copy-on-write) are changed to employ non-temporal stores.
• The swap of root pointer using compare-and-swap is performed by PSwCAS and the accesses to the root pointer are made to check its persistent state.

4. P-ART

• Final commit stores (setting a value entry within a node or swapping a parent pointer for node exchange) are changed to employ non-temporal stores.