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// Copyright 2017 Yahoo Holdings. 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) {
for (VespaBackEndSearcher n : oldNodes) {
if (n == node) return oldNodes; // already present
}
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.
* @param node the backend searcher (must never be null)
*/
public void add(VespaBackEndSearcher node) {
allNodes = addNode(node, allNodes);
if (node.isLocalDispatching()) {
localNodes = addNode(node, localNodes);
}
}
private VespaBackEndSearcher[] removeNode(VespaBackEndSearcher node, VespaBackEndSearcher[] oldNodes) {
int newLen = oldNodes.length;
for (VespaBackEndSearcher n : oldNodes) {
if (n == node) {
--newLen;
}
}
if (newLen == oldNodes.length) {
return oldNodes;
}
VespaBackEndSearcher[] newNodes = new VespaBackEndSearcher[newLen];
int idx = 0;
for (VespaBackEndSearcher n : oldNodes) {
if (n != node) {
newNodes[idx++] = n;
}
}
assert idx == newLen;
return newNodes;
}
/** 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 for skipping (ignored in current implementation)
* @return the selected node, or null if this hasher has no nodes
*/
public VespaBackEndSearcher select(int trynum) {
VespaBackEndSearcher[] nodes = allNodes;
if (localNodes.length > 0) {
nodes = localNodes;
}
if (nodes.length == 0) {
return null;
}
int idx = 0;
if (nodes.length > 1) {
idx = Math.abs(avoidAllQrsHitSameTld.incrementAndGet() % nodes.length);
}
return nodes[idx];
}
}
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