The main operations of the HStoreCoordinator are:
Send a request to all partitions to notify them that a transaction needs to access them as part of a distributed transaction. The HStoreCoordinator will not release the transaction back to the HStoreSite until all of the partitions acknowledge that they are blocked for that transaction.
The transaction is requesting that a partition on another HStoreSite execute a PlanFragment of a query. This is only invoked for remote partitions (i.e., not managed by the same HStoreSite as the transaction’s base partition).
Perform the PREPARE phase of the two-phase commit protocol for a distributed transaction. This signals to a partition that a distributed transaction is finishd with that partition and will not be returning to it to execute further queries. Note that this step is skipped for aborted transactions.
The final FINISH phase of the two-phase commit protocol for distributed transactions. This is always invoked for each distributed regardless of whether it completed successfully or aborted.