http://kb.linux-vs.org/wiki?title=Least-Connection_Scheduling&feed=atom&action=historyLeast-Connection Scheduling - Revision history2024-03-29T06:25:21ZRevision history for this page on the wikiMediaWiki 1.26.2http://kb.linux-vs.org/wiki?title=Least-Connection_Scheduling&diff=348&oldid=prevWensong at 02:37, 1 October 20052005-10-01T02:37:41Z<p></p>
<table class='diff diff-contentalign-left'>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 02:37, 1 October 2005</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1" >Line 1:</td>
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<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The least-connection scheduling algorithm directs network connections to the server with the least number of established connections. This is one of the dynamic scheduling algorithms; because it needs to count the number of connections for each server dynamically to estimate its load. The load balancer records the connection number of each server, increases the connection number of a server when a new connection is dispatched to it, and decrease the connection number of a server when a connection finishs or timeouts.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The least-connection scheduling algorithm directs network connections to the server with the least number of established connections. This is one of the dynamic scheduling algorithms; because it needs to count the number of connections for each server dynamically to estimate its load. The <ins class="diffchange diffchange-inline">[[</ins>load balancer<ins class="diffchange diffchange-inline">]] </ins>records the connection number of each server, increases the connection number of a server when a new connection is dispatched to it, and decrease the connection number of a server when a connection finishs or timeouts.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>In the [[IPVS]] implementation, an extra condition was introduced in the least-connection scheduling to check if a server is available or not, because a server may be taken out of service for either masking server failure or system maintenance. The server weight zero indicates that this server is not available. The formal procedure of round-robin scheduling is as follows:</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>In the [[IPVS]] implementation, an extra condition was introduced in the least-connection scheduling to check if a server is available or not, because a server may be taken out of service for either masking server failure or system maintenance. The server weight zero indicates that this server is not available. The formal procedure of round-robin scheduling is as follows:</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l19" >Line 19:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>  return NULL;</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>  return NULL;</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>For a [[IPVS]] cluster that has a collection of servers with similar performance, least-connection scheduling is good to smooth distribution when the load of requests vary a lot. The load balancer will direct requests to the real server with the fewest connections.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>For a [[IPVS]] cluster that has a collection of servers with similar performance, least-connection scheduling is good to smooth distribution when the load of requests vary a lot. The <ins class="diffchange diffchange-inline">[[</ins>load balancer<ins class="diffchange diffchange-inline">]] </ins>will direct requests to the real server with the fewest connections.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>At a first glance it might seem that least-connection scheduling can also perform well even when there are servers of various processing capacities, because the faster server will get more network connections. In fact, it cannot perform very well because of the TCP's TIME_WAIT state. The TCP's TIME_WAIT is usually 2 minutes, during this 2 minutes a busy web site often receives thousands of connections, for example, the server A is twice as powerful as the server B, the server A is processing thousands of requests and keeping them in the TCP's TIME_WAIT state, but server B is crawling to get its thousands of connections finished. So, the least-connection scheduling cannot get load well balanced among servers with various processing capacities.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>At a first glance it might seem that least-connection scheduling can also perform well even when there are servers of various processing capacities, because the faster server will get more network connections. In fact, it cannot perform very well because of the TCP's TIME_WAIT state. The TCP's TIME_WAIT is usually 2 minutes, during this 2 minutes a busy web site often receives thousands of connections, for example, the server A is twice as powerful as the server B, the server A is processing thousands of requests and keeping them in the TCP's TIME_WAIT state, but server B is crawling to get its thousands of connections finished. So, the least-connection scheduling cannot get load well balanced among servers with various processing capacities.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Job Scheduling Algorithms]]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Job Scheduling Algorithms]]</div></td></tr>
</table>Wensonghttp://kb.linux-vs.org/wiki?title=Least-Connection_Scheduling&diff=188&oldid=prevWensong at 01:47, 30 July 20052005-07-30T01:47:08Z<p></p>
<table class='diff diff-contentalign-left'>
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<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 01:47, 30 July 2005</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1" >Line 1:</td>
<td colspan="2" class="diff-lineno">Line 1:</td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The least-connection scheduling algorithm directs network connections to the server with the least number of established connections. This is one of the dynamic scheduling algorithms; because it needs to count <del class="diffchange diffchange-inline">live </del>connections for each server dynamically. <del class="diffchange diffchange-inline">For </del>a <del class="diffchange diffchange-inline">Virtual Server </del>that is <del class="diffchange diffchange-inline">managing </del>a collection of servers with similar performance, least-connection scheduling is good to smooth distribution when the load of requests vary a lot. <del class="diffchange diffchange-inline">Virtual Server </del>will direct requests to the real server with the fewest <del class="diffchange diffchange-inline">active </del>connections.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The least-connection scheduling algorithm directs network connections to the server with the least number of established connections. This is one of the dynamic scheduling algorithms; because it needs to count <ins class="diffchange diffchange-inline">the number of </ins>connections for each server dynamically <ins class="diffchange diffchange-inline">to estimate its load</ins>. <ins class="diffchange diffchange-inline">The load balancer records the connection number of each server, increases the connection number of </ins>a <ins class="diffchange diffchange-inline">server when a new connection is dispatched to it, and decrease the connection number of a server when a connection finishs or timeouts.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">In the [[IPVS]] implementation, an extra condition was introduced in the least-connection scheduling to check if a server is available or not, because a server may be taken out of service for either masking server failure or system maintenance. The server weight zero indicates </ins>that <ins class="diffchange diffchange-inline">this server </ins>is <ins class="diffchange diffchange-inline">not available. The formal procedure of round-robin scheduling is as follows:</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> Supposing that there is a server set S = {S0, S1, ..., Sn-1},</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> W(Si) is the weight of server Si,</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> C(Si) is the current connection number of server Si,</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> </ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> for (m = 0; m < n; m++) {</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">    if (W(Sm) > 0) {</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">        for (i = m+1; i < n; i++) {</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">            if (W(Si) <= 0)</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">                continue;</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">            if (C(Si) < C(Sm))</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">                m = i;</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">        }</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">        return Sm;</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">    }</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> }</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> return NULL;</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">For a [[IPVS]] cluster that has </ins>a collection of servers with similar performance, least-connection scheduling is good to smooth distribution when the load of requests vary a lot. <ins class="diffchange diffchange-inline">The load balancer </ins>will direct requests to the real server with the fewest connections.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>At a first glance it might seem that least-connection scheduling can also perform well even when there are servers of various processing capacities, because the faster server will get more network connections. In fact, it cannot perform very well because of the TCP's TIME_WAIT state. The TCP's TIME_WAIT is usually 2 minutes, during this 2 minutes a busy web site often receives thousands of connections, for example, the server A is twice as powerful as the server B, the server A is processing thousands of requests and keeping them in the TCP's TIME_WAIT state, but server B is crawling to get its thousands of connections finished. So, the least-connection scheduling cannot get load well balanced among servers with various processing capacities.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>At a first glance it might seem that least-connection scheduling can also perform well even when there are servers of various processing capacities, because the faster server will get more network connections. In fact, it cannot perform very well because of the TCP's TIME_WAIT state. The TCP's TIME_WAIT is usually 2 minutes, during this 2 minutes a busy web site often receives thousands of connections, for example, the server A is twice as powerful as the server B, the server A is processing thousands of requests and keeping them in the TCP's TIME_WAIT state, but server B is crawling to get its thousands of connections finished. So, the least-connection scheduling cannot get load well balanced among servers with various processing capacities.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Job Scheduling Algorithms]]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Job Scheduling Algorithms]]</div></td></tr>
</table>Wensonghttp://kb.linux-vs.org/wiki?title=Least-Connection_Scheduling&diff=90&oldid=prevWensong at 10:37, 20 July 20052005-07-20T10:37:02Z<p></p>
<p><b>New page</b></p><div>The least-connection scheduling algorithm directs network connections to the server with the least number of established connections. This is one of the dynamic scheduling algorithms; because it needs to count live connections for each server dynamically. For a Virtual Server that is managing a collection of servers with similar performance, least-connection scheduling is good to smooth distribution when the load of requests vary a lot. Virtual Server will direct requests to the real server with the fewest active connections.<br />
<br />
At a first glance it might seem that least-connection scheduling can also perform well even when there are servers of various processing capacities, because the faster server will get more network connections. In fact, it cannot perform very well because of the TCP's TIME_WAIT state. The TCP's TIME_WAIT is usually 2 minutes, during this 2 minutes a busy web site often receives thousands of connections, for example, the server A is twice as powerful as the server B, the server A is processing thousands of requests and keeping them in the TCP's TIME_WAIT state, but server B is crawling to get its thousands of connections finished. So, the least-connection scheduling cannot get load well balanced among servers with various processing capacities.<br />
<br />
[[Category:Job Scheduling Algorithms]]</div>Wensong