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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>It works like this:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Varnish retrieves object and determines it is not cacheable<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Through the “hook” in fetch, you tell varnish that THIS object should be marked as not cacheable for the next 10 seconds<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>3.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The object is delivered to the client<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>4.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>At some other point, within the next 10 seconds, another client request for the same object is received<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>5.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Varnish knows that the object is not in the cache, and not cacheable, so it fetches it directly from the backend (pass)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The hit-for-pass behaviour doesn’t do much else than avoid a unnecessary lookup for the object in the internal cache. Hope this is clear now.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Traian<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> </span><span lang=ZH-CN style='font-size:10.0pt'>彭伟</span><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> [mailto:weipeng.pengw@alibaba-inc.com] <br><b>Sent:</b> Thursday, April 07, 2011 12:39 PM<br><b>To:</b> Traian Bratucu<br><b>Cc:</b> varnish-misc@varnish-cache.org<br><b>Subject:</b> Re: a possible dead cycle?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>i don't express myself well,<br><br>then i talk about in detail the whole process i understand, please help me to check it<o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'>based on the configuration as below:<o:p></o:p></p><pre>sub vcl_fetch {<br> if (!obj.cacheable) {<br> # Limit the lifetime of all 'hit for pass' objects to 10 seconds<br> obj.ttl = 10s;<br> pass;<br> }<br>}<br><br>1) after varnish get the object from the backend server, then the process will enter the hook vcl_fetch accoding to the configuration code above<br><br><o:p></o:p></pre><pre><br>2) if the obj is not cacheable, then varnish switch to "pass mode" accoding to the configuration code above<br> <br>3) entering the pass model means varnish will get the object from the backend server again?<br><br><o:p></o:p></pre><p class=MsoNormal style='margin-bottom:12.0pt'><br><br><o:p></o:p></p><div><p class=MsoNormal><span lang=ZH-CN>在</span> 2011<span lang=ZH-CN>年</span>4<span lang=ZH-CN>月</span>7<span lang=ZH-CN>日 下午</span>6:10<span lang=ZH-CN>，</span>Traian Bratucu <<a href="mailto:traian.bratucu@eea.europa.eu">traian.bratucu@eea.europa.eu</a>><span lang=ZH-CN>写道：</span><o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'>Please read the documentation you are referring to. You are talking about <span lang=ZH-CN>“</span>hit for pass<span lang=ZH-CN>”</span> behaviour, it is clearly explained there, in English. Since I cannot explain again in another language, please read it more carefully.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span lang=EN-US style='font-size:10.0pt'>From:</span></b><span lang=EN-US style='font-size:10.0pt'> </span><span lang=ZH-CN style='font-size:10.0pt'>彭伟</span><span lang=EN-US style='font-size:10.0pt'> [mailto:<a href="mailto:pwlazy@gmail.com" target="_blank">pwlazy@gmail.com</a>] <br><b>Sent:</b> Thursday, April 07, 2011 12:05 PM<br><b>To:</b> Traian Bratucu<br><b>Cc:</b> <a href="mailto:varnish-misc@varnish-cache.org" target="_blank">varnish-misc@varnish-cache.org</a><br><b>Subject:</b> Re: a possible dead cycle?</span><o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'>based on the configuration as below:<o:p></o:p></p><pre>sub vcl_fetch {<br> if (!obj.cacheable) {<br> # Limit the lifetime of all 'hit for pass' objects to 10 seconds<br><br><o:p></o:p></pre><pre style='margin-bottom:12.0pt'> obj.ttl = 10s;<br> pass;<br> }<br>}<o:p></o:p></pre><pre><br>when the object is not cacheable, then go to "pass" which means going to fetch the object from the backend server again?<o:p></o:p></pre><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt'> <o:p></o:p></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>2011/4/7 Traian Bratucu <<a href="mailto:traian.bratucu@eea.europa.eu" target="_blank">traian.bratucu@eea.europa.eu</a>><o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'>No, if an object is not cacheable, it will simply not be cached (stored in memory and later served from here instead of fetching from the backend), but IT WILL BE DELIVERED to the client. </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'>The only time varnish will re-fetch the object from the backend is on a new client request.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'>Traian</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span lang=EN-US style='font-size:10.0pt'>From:</span></b><span lang=EN-US style='font-size:10.0pt'> <a href="mailto:varnish-misc-bounces@varnish-cache.org" target="_blank">varnish-misc-bounces@varnish-cache.org</a> [mailto:<a href="mailto:varnish-misc-bounces@varnish-cache.org" target="_blank">varnish-misc-bounces@varnish-cache.org</a>] <b>On Behalf Of </b>??<br><b>Sent:</b> Thursday, April 07, 2011 11:25 AM<br><b>To:</b> <a href="mailto:varnish-misc@varnish-cache.org" target="_blank">varnish-misc@varnish-cache.org</a><br><b>Subject:</b> a possible dead cycle?</span><o:p></o:p></p><div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><br> when varnish fetch a page from backend server, and find it 's not cacheable, so go to fetch the page from backend sever again?<br> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> and find it 's not cacheable again , so again and agian .......?<br><br> please help me! thanks !<br><br> <o:p></o:p></p><pre> Regards! <br> pwlazy<o:p></o:p></pre></div></div></div></div></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><br>_______________________________________________<br>varnish-misc mailing list<br><a href="mailto:varnish-misc@varnish-cache.org" target="_blank">varnish-misc@varnish-cache.org</a><br><a href="http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc" target="_blank">http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc</a><o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div></div></div></div><p class=MsoNormal><br>_______________________________________________<br>varnish-misc mailing list<br><a href="mailto:varnish-misc@varnish-cache.org">varnish-misc@varnish-cache.org</a><br><a href="http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc" target="_blank">http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc</a><o:p></o:p></p></div><p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p><div class=MsoNormal align=center style='text-align:center'><hr size=2 width="100%" align=center></div><p class=MsoNormal><span style='font-size:7.5pt;font-family:"Arial","sans-serif";color:gray'><br>This email (including any attachments) is confidential and may be legally privileged. 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