EclipseLink/UserGuide/JPA/Basic JPA Development/Caching/Query Cache

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Query Results Cache

The EclipseLink query results cache allows the results of named queries to be cached, similar to how objects are cached.

By default in EclipseLink all queries access the database, unless they are by Id, or by cache indexed fields. The resulting rows will still be resolved with the cache, and further queries for relationship will be avoided if the object is cached, but the original query will always access the database. EclipseLink does have options for querying the cache, but these options are not used by default, as EclipseLink cannot assume that all of the objects in the database are in the cache. The query results cache allows for non-indexed and result list queries to still benefit from caching.

The query results cache is indexed by the name of the query, and the parameters of the query. Only named queries can have their results cached, dynamic queries cannot use the query results cache. As well, if you modify a named query before execution, such as setting hints or properties, then it cannot use the cached results.

The query results cache does not pick up committed changes from the application as the object cache does. It should only be used to cache read-only objects, or should use an invalidation policy to avoid caching stale results. Committed changes to the objects in the result set will still be picked up, by changes that affect the results set (such as new or changed objects that should be added/removed from the result set) will not be picked up.

The query results cache supports a fixed size, cache type, and invalidation options.

Configuring Query Results Cache

The query results cache is configured through query hints.

Query Results Cache Query Hints

Hint	Description	Default	Required?
eclipselink.query-results-cache	Enable query results cache for the named query.	no cached results	Required
eclipselink.query-results-cache.size	Sets the fixed size of the query results cache for the named query. The size is the number of queries with unique parameters to cache. If the query has no parameters, a value of 1 should be used.	100	Optional
eclipselink.query-results-cache.expiry	Sets the expiry time in milliseconds of the cached results.	no expiry	Optional
eclipselink.query-results-cache.expiry-time-of-day	Configures the time of day expiry. Valid values are string time format, "HH:MM:SS".	no expiry	Optional
eclipselink.query-results-cache.randomize-expiry	Set if the expiry time should be randomized by 10% of the set expiry time. This can be used to avoid a bottleneck on a fixed expiry time.	false	Optional
eclipselink.query-results-cache.type	Set the cache type. Valid values are defined in the CacheType enum. Normally an LRU fixed sized CACHE is used, a FULL, WEAK or SOFT cache can also be used.	CACHE	Optional

Query results cache annotation example

...
@Entity
@NamedQuery(
  name="findAllEmployeesInCity",
  query="Select e from Employee e where e.address.city = :city",
  hints={
    @Hint(name="eclipselink.query-results-cache", value="true")
    @Hint(name="eclipselink.query-results-cache.size", value="500")
  })
public class Employee {
  ...
}

Query results cache XML example

<?xml version="1.0"?>
<entity-mappings
	xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/orm"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.eclipse.org/eclipselink/xsds/persistence/orm http://www.eclipse.org/eclipselink/xsds/eclipselink_orm_2_4.xsd"
	version="2.4">
    <entity name="Employee" class="org.acme.Employee" access="FIELD">
        <named-query name="findAllEmployeesInCity" query="Select e from Employee e where e.address.city = :city">
            <hint name="eclipselink.query-results-cache" value="true"/>
            <hint name="eclipselink.query-results-cache.size" value="500"/>
        </named-query>
        ...
    </entity>
</entity-mappings>

Query results cache query example

Query query = em.createNamedQuery("findAllEmployeesInCity");
query.setParameter("city", "Ottawa");
List<Employee> employees = query.getResultList();

Version: 2.4 DRAFT
Other versions...

Cache Indexes	Caching	Query Cache Options and In-memory Querying
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