Github user ajs6f commented on a diff in the pull request:
https://github.com/apache/jena/pull/233#discussion_r110254074
--- Diff:
jena-arq/src/main/java/org/apache/jena/sparql/core/mosaic/DatasetGraphMosaic.java
---
@@ -0,0 +1,589 @@
+package org.apache.jena.sparql.core.mosaic;
+
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+import java.util.WeakHashMap;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+import org.apache.jena.graph.Graph;
+import org.apache.jena.graph.Node;
+import org.apache.jena.query.ReadWrite;
+import org.apache.jena.shared.JenaException;
+import org.apache.jena.shared.Lock;
+import org.apache.jena.sparql.core.DatasetGraph;
+import org.apache.jena.sparql.core.GraphView;
+import org.apache.jena.sparql.core.Quad;
+import org.apache.jena.sparql.core.thrift.IteratorCachedArray;
+import org.apache.jena.sparql.util.Context;
+import org.apache.jena.sparql.util.Symbol;
+import org.slf4j.Logger;
+
+/**
+ * A DatasetGraph which distributes actions across a number of child
DatasetGraph's.
+ *
+ * As Jena requires Thread affinity when working with transactions this
class uses ThreadProxy.
+ *
+ * Most DatasetGraph methods call into a set of convenience methods which
perform common tasks, i.e. mosaicIterator(Function<DatasetGraph, Iterator<T>>).
+ *
+ * @author dick
+ *
+ */
+public class DatasetGraphMosaic implements DatasetGraph {
+
+ private static final Logger LOGGER =
getLogger(DatasetGraphMosaic.class);
+
+ public static final String jenaID = UUID.randomUUID().toString();
+
+ public static final Symbol MOSAIC_STREAM_SEQUENTIAL =
Symbol.create(DatasetGraphMosaic.class.getSimpleName() +
".mosaicStreamSequential");
+
+ public static final Symbol WRAP_ITERATOR =
Symbol.create(DatasetGraphMosaic.class.getSimpleName() + ".wrapIterator");
+
+ protected final String id = UUID.randomUUID().toString();
+
+ protected volatile Boolean closed = false;
+
+ protected final Topology topology = new Topology();
+
+ protected final Set<Tessera> mosaic;
+
+ protected final ThreadLocal<TransactionalDistributed> transactional;
+
+ protected final WeakHashMap<Thread, TransactionalDistributed> monitor;
+
+ protected final Lock lock;
+
+ protected final DatasetGraphShimWrite shimWrite;
+
+ protected final AtomicInteger readCount = new AtomicInteger();
+
+ protected final AtomicInteger writeCount = new AtomicInteger();
+
+ protected final AtomicInteger transactionCount = new AtomicInteger();
+
+ protected final Context context;
+
+ public DatasetGraphMosaic() {
+ super();
+
+ mosaic = ConcurrentHashMap.newKeySet(256);
+
+ transactional = new ThreadLocal<>();
+
+ monitor = new WeakHashMap<>(32);
+
+ lock = new LockMRAndMW();
+
+ shimWrite = new DatasetGraphShimWrite() {
+
+ @Override
+ public void add(final Node g, final Node s, final Node
p, final Node o) {
--- End diff --
Ah, okay, cool, that was one of my biggest questions (sharding policy). I'm
glad to see you've got an extension point ready, nicely done. My immediate
sense would be that we want a policy injection point near here, into which you
could put a type that takes a quad and checks it against some record of the
available "children" and makes that decision.
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