5.3.5. Using Filters in a Sharded Environment

Execute queries on a subset of the available shards in a sharded environment as follows:

Create a sharding strategy to select a subset of IndexManagers depending on filter configurations.
Activate the filter when running the query.

The following is an example of sharding strategy that queries a specific shard if the customer filter is activated:

public class CustomerShardingStrategy implements IndexShardingStrategy {

 // stored IndexManagers in a array indexed by customerID
 private IndexManager[] indexManagers;
 
 public void initialize(Properties properties, IndexManager[] indexManagers) {
   this.indexManagers = indexManagers;
 }

 public IndexManager[] getIndexManagersForAllShards() {
   return indexManagers;
 }

 public IndexManager getIndexManagerForAddition(
     Class<?> entity, Serializable id, String idInString, Document document) {
   Integer customerID = Integer.parseInt(document.getFieldable("customerID").stringValue());
   return indexManagers[customerID];
 }

 public IndexManager[] getIndexManagersForDeletion(
     Class<?> entity, Serializable id, String idInString) {
   return getIndexManagersForAllShards();
 }

  /**
  * Optimization; don't search ALL shards and union the results; in this case, we 
  * can be certain that all the data for a particular customer Filter is in a single
  * shard; return that shard by customerID.
  */
 public IndexManager[] getIndexManagersForQuery(
     FullTextFilterImplementor[] filters) {
   FullTextFilter filter = getCustomerFilter(filters, "customer");
   if (filter == null) {
     return getIndexManagersForAllShards();
   }
   else {
     return new IndexManager[] { indexManagers[Integer.parseInt(
       filter.getParameter("customerID").toString())] };
   }
 }

 private FullTextFilter getCustomerFilter(FullTextFilterImplementor[] filters, String name) {
   for (FullTextFilterImplementor filter: filters) {
     if (filter.getName().equals(name)) return filter;
   }
   return null;
 }
}

public class CustomerShardingStrategy implements IndexShardingStrategy {

 // stored IndexManagers in a array indexed by customerID
 private IndexManager[] indexManagers;
 
 public void initialize(Properties properties, IndexManager[] indexManagers) {
   this.indexManagers = indexManagers;
 }

 public IndexManager[] getIndexManagersForAllShards() {
   return indexManagers;
 }

 public IndexManager getIndexManagerForAddition(
     Class<?> entity, Serializable id, String idInString, Document document) {
   Integer customerID = Integer.parseInt(document.getFieldable("customerID").stringValue());
   return indexManagers[customerID];
 }

 public IndexManager[] getIndexManagersForDeletion(
     Class<?> entity, Serializable id, String idInString) {
   return getIndexManagersForAllShards();
 }

  /**
  * Optimization; don't search ALL shards and union the results; in this case, we 
  * can be certain that all the data for a particular customer Filter is in a single
  * shard; return that shard by customerID.
  */
 public IndexManager[] getIndexManagersForQuery(
     FullTextFilterImplementor[] filters) {
   FullTextFilter filter = getCustomerFilter(filters, "customer");
   if (filter == null) {
     return getIndexManagersForAllShards();
   }
   else {
     return new IndexManager[] { indexManagers[Integer.parseInt(
       filter.getParameter("customerID").toString())] };
   }
 }

 private FullTextFilter getCustomerFilter(FullTextFilterImplementor[] filters, String name) {
   for (FullTextFilterImplementor filter: filters) {
     if (filter.getName().equals(name)) return filter;
   }
   return null;
 }
}

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If the customer filter is present in the example, the query only uses the shard dedicated to the customer. The query returns all shards if the customer filter is not found. The sharding strategy reacts to each filter depending on the provided parameters.

Activate the filter when the query must be run. The filter is a regular filter (as defined in Section 5.3, “Filters”), which filters Lucene results after the query. As an alternate, use a special filter that is passed to the sharding strategy and then ignored for duration of the query. Use the ShardSensitiveOnlyFilter class to declare the filter.

@Indexed
@FullTextFilterDef(name="customer", impl=ShardSensitiveOnlyFilter.class)
public class Customer {
   ...
}

CacheQuery cacheQuery = Search.getSearchManager(cache).getQuery(query,
Customer.class);
cacheQuery.enableFulltextFilter("customer").setParameter("CustomerID", 5);
@SuppressWarnings("unchecked")
List results = query.List();

@Indexed
@FullTextFilterDef(name="customer", impl=ShardSensitiveOnlyFilter.class)
public class Customer {
   ...
}

CacheQuery cacheQuery = Search.getSearchManager(cache).getQuery(query,
Customer.class);
cacheQuery.enableFulltextFilter("customer").setParameter("CustomerID", 5);
@SuppressWarnings("unchecked")
List results = query.List();

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If the ShardSensitiveOnlyFilter filter is used, Lucene filters do not need to be implemented. Use filters and sharding strategies reacting to these filters for faster query execution in a sharded environment.

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5.3.5. Using Filters in a Sharded Environment

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