1 files changed, 135 insertions, 0 deletions
diff --git a/container-search/src/main/java/com/yahoo/prelude/cluster/Hasher.java b/container-search/src/main/java/com/yahoo/prelude/cluster/Hasher.java
new file mode 100644
index 00000000000..a78b5d6e1b5
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+++ b/container-search/src/main/java/com/yahoo/prelude/cluster/Hasher.java
@@ -0,0 +1,135 @@
+// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.prelude.cluster;
+
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.logging.Logger;
+
+import com.yahoo.container.handler.VipStatus;
+import com.yahoo.log.LogLevel;
+import com.yahoo.prelude.fastsearch.VespaBackEndSearcher;
+
+/**
+ * Failover between multiple Vespa backends.
+ *
+ * @author bratseth
+ * @author Prashanth B. Bhat
+ * @author Steinar Knutsen
+ */
+public class Hasher {
+
+    boolean running = false;
+
+    private static final Logger log = Logger.getLogger(Hasher.class.getName());
+    private static final Random tldSeeder = new Random();
+
+    private volatile VespaBackEndSearcher[] allNodes = new VespaBackEndSearcher[0];
+    private volatile VespaBackEndSearcher[] localNodes = new VespaBackEndSearcher[0];
+
+    private AtomicInteger avoidAllQrsHitSameTld = new AtomicInteger(tldSeed());
+
+    /**
+     * Creates a hasher independent of the {@linkplain VipStatus programmatic VIP API}.
+     */
+    public Hasher() {
+    }
+
+    private static synchronized int tldSeed() {
+        return tldSeeder.nextInt();
+    }
+
+    static private VespaBackEndSearcher[] addNode(VespaBackEndSearcher node, VespaBackEndSearcher[] oldNodes) {
+        VespaBackEndSearcher[] newNodes = new VespaBackEndSearcher[oldNodes.length + 1];
+        System.arraycopy(oldNodes, 0, newNodes, 0, oldNodes.length);
+        newNodes[oldNodes.length] = node;
+        return newNodes;
+    }
+    /**
+     * Make a node available for search.
+     */
+    public void add(VespaBackEndSearcher node) {
+        allNodes = addNode(node, allNodes);
+
+        if (node.isLocalDispatching()) {
+            localNodes = addNode(node, localNodes);
+        }
+    }
+
+    private VespaBackEndSearcher[] removeNode(VespaBackEndSearcher node, VespaBackEndSearcher[] nodes) {
+        VespaBackEndSearcher[] newNodes = null;
+        for (VespaBackEndSearcher n : nodes) {
+            if (n == node) {
+                newNodes = new VespaBackEndSearcher[nodes.length - 1];
+                break;
+            }
+        }
+        if (newNodes != null) {
+            int numToKeep = 0;
+
+            for (VespaBackEndSearcher n : nodes) {
+                if (n != node) {
+                    newNodes[numToKeep++] = n;
+                }
+            }
+            return newNodes;
+        }
+        return nodes;
+    }
+
+    /** Removes a node */
+    public void remove(VespaBackEndSearcher node) {
+        if (allNodes.length == 0) {
+            return;
+        }
+
+        VespaBackEndSearcher[] newNodes = removeNode(node, allNodes);
+        if (newNodes != allNodes) {
+            if (running && newNodes.length == 0) {
+                log.log(LogLevel.WARNING, "No longer any nodes for this cluster when"
+                        + " removing malfunctioning " + node.toString() + ".");
+            }
+            allNodes = newNodes;
+        }
+
+        newNodes = removeNode(node, localNodes);
+        if (newNodes != localNodes) {
+            if (running && localNodes.length == 0) {
+                log.log(LogLevel.WARNING, "Removing malfunctioning " + node.toString()
+                        + " from traffic leaves no local dispatchers, performance"
+                        + " degradation is to expected.");
+            }
+            localNodes = newNodes;
+        }
+    }
+
+    public int getNodeCount() {
+        return allNodes.length;
+    }
+
+    /**
+     * Return a node, prefer local nodes, try to skip already hit nodes.
+     *
+     * @param trynum
+     *            hint to skip already used nodes
+     * @return the selected node, or null if this hasher has no nodes
+     */
+    public VespaBackEndSearcher select(int trynum) {
+        VespaBackEndSearcher[] nodes = allNodes;
+
+        if (nodes.length == 0) {
+            return null;
+        } else {
+            if (localNodes.length > 0) {
+                nodes = localNodes;
+                if (localNodes.length == 1) {
+                    return nodes[0];
+                } else {
+                    return nodes[Math.abs(avoidAllQrsHitSameTld.incrementAndGet() % nodes.length)];
+                }
+            } else {
+                return nodes[Math.abs(avoidAllQrsHitSameTld.incrementAndGet() % nodes.length)];
+            }
+        }
+    }
+
+}