// Latency.java
// ------------
// (C) 2009 by Michael Peter Christen; mc@yacy.net
// first published 19.03.2009 on http://yacy.net
//
// $LastChangedDate$
// $LastChangedRevision$
// $LastChangedBy$
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
package de.anomic.crawler;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import de.anomic.plasma.plasmaSwitchboard;
import de.anomic.yacy.yacyURL;
public class Latency {
private static final ConcurrentHashMap<String, Host> map = new ConcurrentHashMap<String, Host>();
public static void update(String hosthash, String host, long time) {
assert hosthash.length() == 6;
Host h = map.get(hosthash);
if (h == null) {
h = new Host(host, time);
map.put(hosthash, h);
} else {
h.update(time);
}
}
public static void update(String hosthash, String host) {
assert hosthash.length() == 6;
Host h = map.get(hosthash);
if (h == null) {
h = new Host(host, 3000);
map.put(hosthash, h);
} else {
h.update();
}
}
public static void slowdown(String hosthash, String host) {
assert hosthash.length() == 6;
Host h = map.get(hosthash);
if (h == null) {
h = new Host(host, 3000);
map.put(hosthash, h);
} else {
h.slowdown();
}
}
public static Host host(String hosthash) {
assert hosthash.length() == 6;
return map.get(hosthash);
}
public static int average(String hosthash) {
assert hosthash.length() == 6;
Host h = map.get(hosthash);
if (h == null) return 1000;
return h.average();
}
public static Iterator<Map.Entry<String, Host>> iterator() {
return map.entrySet().iterator();
}
/**
* calculate the time since the last access of the domain as referenced by the url hash
* @param urlhash
* @return a time in milliseconds since last access of the domain or Long.MAX_VALUE if the domain was not accessed before
*/
public static long lastAccessDelta(final String urlhash) {
assert urlhash.length() == 12 || urlhash.length() == 6;
final Latency.Host host = Latency.host((urlhash.length() == 6) ? urlhash : urlhash.substring(6));
if (host == null) return Long.MAX_VALUE; // never accessed
return System.currentTimeMillis() - host.lastacc();
}
/**
* guess a minimum waiting time
* the time is not correct, because if the domain was not checked yet by the robots.txt delay value, it is too low
* also the 'isCGI' property is missing, because the full text of the domain is unknown here
* @param urlhash
* @param minimumLocalDelta
* @param minimumGlobalDelta
* @return the remaining waiting time in milliseconds. The return value may be negative
* which expresses how long the time is over the minimum waiting time.
*/
public static long waitingRemainingGuessed(String hosthash, final long minimumLocalDelta, final long minimumGlobalDelta) {
assert hosthash.length() == 12 || hosthash.length() == 6;
Host host = Latency.host((hosthash.length() == 6) ? hosthash : hosthash.substring(6));
if (host == null) return 0;
// the time since last access to the domain is the basis of the remaining calculation
final long timeSinceLastAccess = System.currentTimeMillis() - host.lastacc();
// find the minimum waiting time based on the network domain (local or global)
final boolean local = yacyURL.isLocal(hosthash);
long waiting = (local) ? minimumLocalDelta : minimumGlobalDelta;
// if we have accessed the domain many times, get slower (the flux factor)
if (!local) waiting += host.flux(waiting);
// use the access latency as rule how fast we can access the server
// this applies also to localhost, but differently, because it is not necessary to
// consider so many external accesses
waiting = Math.max(waiting, (local) ? host.average() / 2 : host.average() * 2);
// prevent that that a robots file can stop our indexer completely
waiting = Math.min(60000, waiting);
// return time that is remaining
//System.out.println("Latency: " + (waiting - timeSinceLastAccess));
return waiting - timeSinceLastAccess;
}
/**
* calculates how long should be waited until the domain can be accessed again
* this follows from:
* - given minimum access times
* - the fact that an url is a CGI url or not
* - the times that the domain was accessed (flux factor)
* - the response latency of the domain
* - and a given minimum access time as given in robots.txt
* @param minimumLocalDelta
* @param minimumGlobalDelta
* @return the remaining waiting time in milliseconds
*/
public static long waitingRemaining(yacyURL url, final long minimumLocalDelta, final long minimumGlobalDelta) {
// first check if the domain was _ever_ accessed before
String hosthash = url.hash().substring(6);
Host host = host(hosthash);
if (host == null) return 0; // no delay
// the time since last access to the domain is the basis of the remaining calculation
final long timeSinceLastAccess = System.currentTimeMillis() - host.lastacc();
// find the minimum waiting time based on the network domain (local or global)
final boolean local = url.isLocal();
long waiting = (local) ? minimumLocalDelta : minimumGlobalDelta;
// for CGI accesses, we double the minimum time
// mostly there is a database access in the background
// which creates a lot of unwanted IO on target site
if (url.isCGI()) waiting = waiting * 2;
// if we have accessed the domain many times, get slower (the flux factor)
if (!local) waiting += host.flux(waiting);
// find the delay as given by robots.txt on target site
long robotsDelay = (local) ? 0 : plasmaSwitchboard.getSwitchboard().robots.crawlDelayMillis(url);
waiting = Math.max(waiting, robotsDelay);
// use the access latency as rule how fast we can access the server
// this applies also to localhost, but differently, because it is not necessary to
// consider so many external accesses
waiting = Math.max(waiting, (local) ? host.average() / 2 : host.average() * 2);
// prevent that that a robots file can stop our indexer completely
waiting = Math.min(60000, waiting);
// return time that is remaining
//System.out.println("Latency: " + (waiting - timeSinceLastAccess));
return Math.max(0, waiting - timeSinceLastAccess);
}
public static final class Host {
private long timeacc;
private long lastacc;
private int count;
private String host;
private long robotsMinDelay;
public Host(String host, long time) {
this.host = host;
this.timeacc = time;
this.count = 1;
this.lastacc = System.currentTimeMillis();
this.robotsMinDelay = 0;
}
public void update(long time) {
this.lastacc = System.currentTimeMillis();
this.timeacc += time;
this.count++;
}
public void update() {
this.lastacc = System.currentTimeMillis();
}
public void slowdown() {
this.lastacc = System.currentTimeMillis();
this.timeacc = Math.min(60000, average() * 2);
this.count = 1;
}
public int count() {
return this.count;
}
public int average() {
return (int) (this.timeacc / this.count);
}
public long lastacc() {
return this.lastacc;
}
public String host() {
return this.host;
}
public void robotsDelay(long ur) {
this.robotsMinDelay = ur;
}
public long robotsDelay() {
return this.robotsMinDelay;
}
public long flux(long range) {
return count >= 1000 ? range * Math.min(5000, count) / 1000 : range / (1000 - count);
}
}
}