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Indexing

Hazelcast distributed queries will run on each member in parallel and only results will return the conn. When a query runs on a member, Hazelcast will iterate through the entire owned entries and find the matching ones. This can be made faster by indexing the mostly queried fields. Just like you would do for your database. Of course, indexing will add overhead for each write operation but queries will be a lot faster. If you are querying your map a lot, make sure to add indexes for most frequently queried fields. So, if your active and age < 30 query, for example, is used a lot, make sure you add index for active and age fields. Here is how:

IMap imap = Hazelcast.getMap("employees");
imap.addIndex("age", true);        // ordered, since we have ranged queries for this field
imap.addIndex("active", false);    // not ordered, because boolean field cannot have range

IMap.addIndex(fieldName, ordered) is used for adding index. For each indexed field, if you have ranged queries such as age>30, age BETWEEN 40 AND 60, then ordered parameter should betrue. Otherwise, set it tofalse.

Also, you can define IMap indexes in configuration.

  • Hazelcast XML configuration

    <map name="default">
    ...
    <indexes>
        <index ordered="false">name</index>
        <index ordered="true">age</index>
    </indexes>
</map>

  • API Configuration

    mapConfig.addMapIndexConfig(new MapIndexConfig("name", false));
mapConfig.addMapIndexConfig(new MapIndexConfig("age", true));

  • Spring XML configuration

    <hz:map name="default">
    <hz:indexes>
        <hz:index attribute="name"/>
        <hz:index attribute="age" ordered="true"/>
    </hz:indexes>
</hz:map>