Checking if all QueryCaches received updates from IMap in a Hazelcast cluster

Question

Having a Hazelcast cluster, how do I make sure that the changes I made to an IMap are completely propagated to QueryCaches on all of the cluster nodes, before I invoke an EntryProcessor that uses the changed data from those QueryCaches?

A simplified scenario of what I'm trying to achieve:

• I have an algorithm that revalues items based on some parameters
• There are up to one billion items so they are kept in an IMap
• There are a hundred thousands parameters also kept in an IMap
• Each node has a complete copy of all parameters in the form of QueryCache to speed things up
• A request to the app comes in, to change a couple of parameters and revalue all items
• Parameters are changed by simple map.put(), then the algorithm in the form of EntryProcessor is invoked on the items on each node
• This won't work, as the updates to QueryCache are asynchronous, so sometimes the algorithm will use old parameter values

public void handleRevaluationRequest(Object parametersChangeInstructions) {
    TransactionContext transaction = hazelcastInstance.newTransactionContext();
    transaction.beginTransaction();
    TransactionalMap parameters = transaction.getMap("parameters");
    parameters.set(...); // changes to a few parameters
    parameters.put(...); // adding a few different parameters
    transaction.commitTransaction();

    IMap items = hazelcastInstance.getMap("items");
    items.executeOnEntries(new RevaluationProcessor());
    // processor uses new and/or existing parameters from QueryCache to revalue items
    // but won't always see the changes to parameters that we've just made
}

Is there a way to achieve something like that? Maybe instead of QueryCache using a different data structure will be more appriopriate to achieve synchronous "replication" of reference data that can be used by EntryProcessor.

Answer 1

When you do a map.put and run EntryProcessor afterwards, the EP runs on the key-value store on server side, so it always works on the last updated value on server. Update to QueryCache via map.put is asynchronous and not related to what you do in EntryProcessor and when.

Additionally for your information, EntryProcessor runs on partition thread, which means the thread that is responsible for updating the value is also responsible for running the EntryProcessor. So, while an EntryProcessor is running, no other thread can update that value.