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Merge pull request #379 from LiUSemWeb/378-persisted-disk-cache-for-cardinality-queries
378 persisted disk cache for cardinality queries
2 parents 2784cb4 + 20bd44e commit 0004f28

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‎hefquin-base/src/main/java/se/liu/ida/hefquin/base/datastructures/PersistableCache.java

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package se.liu.ida.hefquin.base.datastructures;
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/**
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* A generic interface for data structures that can be used as a persisted cache
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* for objects of a specific type. Implementations of this interface may employ
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* their particular policies for cache replacement and for cache invalidation.
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*
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* @param <IdType> the type of the values by which the cached objects can be identified
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* @param <ObjectType> the type of the objects to be maintained in this cache
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*/
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public interface PersistableCache<IdType, ObjectType> extends Cache<IdType, ObjectType> {
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/**
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* Saves the current state of the cache to persistent storage.
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* Implementations may choose different mechanisms for persistence,
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* such as writing to a file or a database.
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*
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* This method should ensure that all cached data is synchronized with
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* persistent storage. Depending on the implementation, synchronization
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* may be automatic or explicitly controlled.
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*/
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void save();
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/**
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* Loads the cache state from persistent storage.
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* If persistent data exists, it should be restored into the cache.
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* Implementations should handle cases where no prior state exists
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* gracefully.
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*/
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void load();
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}

‎hefquin-engine/src/main/java/se/liu/ida/hefquin/engine/federation/access/impl/CardinalityCacheKey.java

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package se.liu.ida.hefquin.engine.federation.access.impl;
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import java.io.Serializable;
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import java.util.Objects;
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import se.liu.ida.hefquin.engine.federation.BRTPFServer;
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import se.liu.ida.hefquin.engine.federation.FederationMember;
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import se.liu.ida.hefquin.engine.federation.SPARQLEndpoint;
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import se.liu.ida.hefquin.engine.federation.TPFServer;
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import se.liu.ida.hefquin.engine.federation.access.BRTPFRequest;
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import se.liu.ida.hefquin.engine.federation.access.DataRetrievalRequest;
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import se.liu.ida.hefquin.engine.federation.access.SPARQLRequest;
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import se.liu.ida.hefquin.engine.federation.access.TPFRequest;
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/**
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* A key for caching cardinality requests, uniquely identified by a {@link DataRetrievalRequest} and a {@link FederationMember}.
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*/
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public class CardinalityCacheKey implements Serializable {
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private static final long serialVersionUID = 1L;
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protected final String query;
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protected final String url;
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protected final String bindings;
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public CardinalityCacheKey( final DataRetrievalRequest req, final FederationMember fm ) {
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if ( req instanceof SPARQLRequest sparqlRequest && fm instanceof SPARQLEndpoint sparqlEndpoint ) {
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query = sparqlRequest.toString();
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url = sparqlEndpoint.getInterface().getURL();
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bindings = "";
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}
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else if ( req instanceof TPFRequest tpfRequest ) {
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query = tpfRequest.toString();
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bindings = "";
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if ( fm instanceof TPFServer tpfServer ) {
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url = tpfServer.getInterface().createRequestURL( tpfRequest );
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}
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else if ( fm instanceof BRTPFServer brtpfServer ) {
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url = brtpfServer.getInterface().createRequestURL( tpfRequest );
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}
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else {
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throw new IllegalArgumentException( "Unexpected type of server: " + fm.getClass().getName() );
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}
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}
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else if ( req instanceof BRTPFRequest brtpfRequest && fm instanceof BRTPFServer brtpfServer ) {
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query = brtpfRequest.getTriplePattern().toString();
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url = brtpfServer.getInterface().createRequestURL( brtpfRequest );
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bindings = brtpfRequest.getSolutionMappings().toString();
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}
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else {
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throw new IllegalArgumentException( "Unexpected request type: " + req.getClass().getName() + "(server type: " + fm.getClass().getName() + ")" );
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}
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}
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@Override
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public boolean equals( Object obj ) {
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if ( this == obj )
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return true;
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if ( obj == null || getClass() != obj.getClass() )
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return false;
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CardinalityCacheKey other = (CardinalityCacheKey) obj;
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return query.equals( other.query ) && url.equals( other.url );
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}
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@Override
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public int hashCode() {
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return Objects.hash( query, url );
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}
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@Override
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public String toString() {
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return "CardinalityCacheKey{query='" + query + "', url='" + url + "', bindings='" + bindings + "'}";
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}
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}

‎hefquin-engine/src/main/java/se/liu/ida/hefquin/engine/federation/access/impl/FederationAccessManagerWithPersistedDiskCache.java

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package se.liu.ida.hefquin.engine.federation.access.impl;
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import java.util.concurrent.CompletableFuture;
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import java.util.concurrent.ExecutorService;
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import se.liu.ida.hefquin.base.datastructures.impl.cache.CacheEntry;
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import se.liu.ida.hefquin.base.datastructures.impl.cache.CachePolicies;
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import se.liu.ida.hefquin.engine.federation.BRTPFServer;
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import se.liu.ida.hefquin.engine.federation.SPARQLEndpoint;
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import se.liu.ida.hefquin.engine.federation.TPFServer;
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import se.liu.ida.hefquin.engine.federation.access.BRTPFRequest;
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import se.liu.ida.hefquin.engine.federation.access.CardinalityResponse;
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import se.liu.ida.hefquin.engine.federation.access.DataRetrievalResponse;
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import se.liu.ida.hefquin.engine.federation.access.FederationAccessException;
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import se.liu.ida.hefquin.engine.federation.access.FederationAccessManager;
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import se.liu.ida.hefquin.engine.federation.access.SPARQLRequest;
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import se.liu.ida.hefquin.engine.federation.access.TPFRequest;
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/**
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* A FederationAccessManager implementation that incorporates persistent disk
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* caching of SPARQL cardinality requests.
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*
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* TODO: The implementation uses a simple serialization/deserialization
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* strategy, where the file is stored to disk by writing the full map to disk
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* for each update. This approach is not optimized for this task but is simply
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* intended as a proof of concept. A future implementation should support
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* standard cache configuration policys, such as time-based eviction (time to
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* live), but should leverage an optimized persistence strategy, preferably
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* leveraging a libary.
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*
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* Note: Most of the classes/interfaces involved (e.g., DataRetrievalResponse,
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* CardinalityResponse etc.) do not support serialization.
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*/
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public class FederationAccessManagerWithPersistedDiskCache extends FederationAccessManagerWithCache
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{
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protected final PersistableCardinalityCacheImpl<CardinalityCacheKey> cardinalityCache;
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public FederationAccessManagerWithPersistedDiskCache( final FederationAccessManager fedAccMan,
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final int cacheCapacity,
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final CachePolicies<Key, CompletableFuture<? extends DataRetrievalResponse>, ? extends CacheEntry<CompletableFuture<? extends DataRetrievalResponse>>> cachePolicies )
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{
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super( fedAccMan, cacheCapacity, cachePolicies );
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cardinalityCache = new PersistableCardinalityCacheImpl<>();
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}
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public FederationAccessManagerWithPersistedDiskCache( final FederationAccessManager fedAccMan,
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final int cacheCapacity )
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{
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this( fedAccMan, cacheCapacity, new MyDefaultCachePolicies() );
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}
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/**
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* Creates a {@link FederationAccessManagerWithPersistedDiskCache} with a default configuration.
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*/
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public FederationAccessManagerWithPersistedDiskCache( final ExecutorService execService )
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{
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this( new AsyncFederationAccessManagerImpl( execService ), 100, new MyDefaultCachePolicies() );
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}
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@Override
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public CompletableFuture<CardinalityResponse> issueCardinalityRequest( final SPARQLRequest req,
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final SPARQLEndpoint fm )
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throws FederationAccessException
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{
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final CardinalityCacheKey key = new CardinalityCacheKey( req, fm );
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final CompletableFuture<CardinalityResponse> cachedResponse = cardinalityCache.get( key );
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if ( cachedResponse != null ) {
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cacheHitsSPARQLCardinality++;
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return cachedResponse;
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}
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final CompletableFuture<CardinalityResponse> newResponse = fedAccMan.issueCardinalityRequest( req, fm );
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cardinalityCache.put( key, newResponse );
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newResponse.thenRun( () -> cardinalityCache.save() );
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return newResponse;
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}
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@Override
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public CompletableFuture<CardinalityResponse> issueCardinalityRequest( final TPFRequest req,
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final TPFServer fm )
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throws FederationAccessException
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{
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final CardinalityCacheKey key = new CardinalityCacheKey( req, fm );
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final CompletableFuture<CardinalityResponse> cachedResponse = cardinalityCache.get( key );
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if ( cachedResponse != null ) {
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cacheHitsTPFCardinality++;
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return cachedResponse;
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}
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final CompletableFuture<CardinalityResponse> newResponse = fedAccMan.issueCardinalityRequest( req, fm );
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cardinalityCache.put( key, newResponse );
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newResponse.thenRun( () -> cardinalityCache.save() );
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return newResponse;
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}
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@Override
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public CompletableFuture<CardinalityResponse> issueCardinalityRequest( final TPFRequest req,
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final BRTPFServer fm )
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throws FederationAccessException
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{
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final CardinalityCacheKey key = new CardinalityCacheKey( req, fm );
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final CompletableFuture<CardinalityResponse> cachedResponse = cardinalityCache.get( key );
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if ( cachedResponse != null ) {
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cacheHitsTPFCardinality++;
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return cachedResponse;
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}
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final CompletableFuture<CardinalityResponse> newResponse = fedAccMan.issueCardinalityRequest( req, fm );
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cardinalityCache.put( key, newResponse );
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newResponse.thenRun( () -> cardinalityCache.save() );
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return newResponse;
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}
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@Override
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public CompletableFuture<CardinalityResponse> issueCardinalityRequest( final BRTPFRequest req,
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final BRTPFServer fm )
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throws FederationAccessException
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{
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final CardinalityCacheKey key = new CardinalityCacheKey( req, fm );
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final CompletableFuture<CardinalityResponse> cachedResponse = cardinalityCache.get( key );
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if ( cachedResponse != null ) {
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cacheHitsBRTPFCardinality++;
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return cachedResponse;
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}
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final CompletableFuture<CardinalityResponse> newResponse = fedAccMan.issueCardinalityRequest( req, fm) ;
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cardinalityCache.put( key, newResponse );
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newResponse.thenRun( () -> cardinalityCache.save() );
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return newResponse;
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}
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/**
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* Clears the persisted cardinality cache map.
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*/
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public void clearCardinalityCache(){
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cardinalityCache.clear();
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cardinalityCache.save();
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}
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}

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