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  1. mod_cluster
  2. MODCLUSTER-372

Number of registered contexts negatively affects mod_cluster performance

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      There is a performance concern regarding CPU usage on the Apache HTTP Server with mod_cluster set up as a load balancer. Perf tests revealed that the major variable affecting the CPU usage is the overall number of registered contexts. It's noteworthy that these contexts actually don't need to be accessed at all, it's enough that they are present.

      The first test 9 workers, 31 contexts, round robin depicts a behavior where all contexts are being accessed in a round robin fashion. Note the CPU usage. If we compare it to the 9 workers, 1 context test, it becomes apparent that there is something wrong with the CPU usage. As it is clear from the 9 workers, 31 contexts, access 1 test, accessing only one of these contexts doesn't help much.

      The last two tests, 4 workers, 61 contexts, accessing 1 and 4 workers, 1 context confirm the results, environment differs only in number of nodes and number of contexts.

      httpd.conf attached, stay tuned for some profiler outputs...

      9 workers, 31 contexts, round robin

      Nodes Sessions Ses.Active Samples samples/s mean resp. ms max resp. ms conn. errors valid samples %
      9 150 150 8843 147.4 15 60 0 8843 100%
      9 250 250 14422 240.3 37 215 0 14422 100%
      9 350 350 17551 292.5 196 443 0 17551 100%
      9 450 450 21303 355.0 269 603 0 21303 100%
      9 550 550 24818 413.6 325 686 0 24818 100%
      9 650 650 26804 446.7 469 800 0 26804 100%
      9 750 750 29930 498.8 507 985 0 29930 100%
      9 850 850 30665 511.0 665 1185 0 30665 100%
      9 950 950 34421 573.6 647 1316 0 34421 100%
      9 1050 1050 35067 584.4 800 1487 0 35067 100%
      9 1150 1150 36024 600.4 925 1612 0 36024 100%
      9 1250 1250 36635 610.5 1030 1815 0 36635 100%
      9 1350 1350 38395 639.9 1096 1942 0 38395 100%
      9 1450 1450 39713 661.8 1170 2466 0 39713 100%
      9 1550 1550 39455 657.5 1392 2340 0 39455 100%
      9 1650 1650 39849 664.1 1465 4240 0 39849 100%
      9 1750 1750 42435 707.2 1454 6511 0 42435 100%
      9 1850 1850 44714 745.2 1498 4866 0 44714 100%
      9 1950 1911 46072 767.8 1554 43016 0 46072 100%
      9 2050 1911 44496 741.5 1617 4953 39 44457 99%
      9 2150 1911 43715 728.5 1632 5348 125 43590 99%
      9 2250 1911 41112 685.1 1764 9800 155 40957 99%

      9 workers, 31 contexts, accessing only one of them

      Nodes Sessions Ses.Active Samples samples/s mean resp. ms max resp. ms conn. errors valid samples %
      9 150 150 8954 149.2 4 42 0 8954 100%
      9 250 250 14897 248.3 7 33 0 14897 100%
      9 350 350 20784 346.4 8 68 0 20784 100%
      9 450 450 26748 445.8 8 69 0 26748 100%
      9 550 550 32553 542.5 11 92 0 32553 100%
      9 650 650 38558 642.6 10 60 0 38558 100%
      9 750 750 43571 726.1 29 329 0 43571 100%
      9 850 850 46133 768.8 99 494 0 46133 100%
      9 950 950 50854 847.5 120 501 0 50854 100%
      9 1050 1050 54451 907.4 154 584 0 54451 100%
      9 1150 1150 59961 999.3 138 674 0 59961 100%
      9 1250 1250 62567 1,042.6 198 675 0 62567 100%
      9 1350 1350 61939 1,032.2 301 799 0 61939 100%
      9 1450 1450 67920 1,131.9 276 844 0 67920 100%
      9 1550 1550 73151 1,219.1 261 861 0 73151 100%
      9 1650 1650 73937 1,232.2 332 955 0 73937 100%
      9 1750 1750 73516 1,225.2 423 1046 0 73516 100%
      9 1850 1850 72556 1,209.1 515 1264 0 72556 100%
      9 1950 1911 78613 1,310.1 454 50273 0 78613 100%
      9 2050 1911 80141 1,335.6 431 1225 39 80102 99%
      9 2150 1911 76979 1,282.9 490 1338 127 76852 99%
      9 2250 1911 78048 1,300.7 464 1305 136 77912 99%

      9 workers, 1 context

      Nodes Sessions Ses.Active Samples samples/s mean resp. ms max resp. ms conn. errors valid samples %
      9 150 150 8965 149.4 2 12 0 8965 100%
      9 250 250 14965 249.4 2 22 0 14965 100%
      9 350 350 20950 349.1 2 23 0 20950 100%
      9 450 450 26941 449.0 2 26 0 26941 100%
      9 550 550 32937 548.9 1 26 0 32937 100%
      9 650 650 38900 648.3 1 19 0 38900 100%
      9 750 750 44918 748.6 1 11 0 44918 100%
      9 850 850 50902 848.3 2 22 0 50902 100%
      9 950 950 56878 947.9 1 14 0 56878 100%
      9 1050 1050 62874 1,047.8 2 12 0 62874 100%
      9 1150 1150 68845 1,147.3 2 99 0 68845 100%
      9 1250 1250 74851 1,247.4 2 103 0 74851 100%
      9 1350 1350 80826 1,347.0 2 100 0 80826 100%
      9 1450 1450 86806 1,446.7 2 19 0 86806 100%
      9 1550 1550 92817 1,546.8 2 52 0 92817 100%
      9 1650 1650 98774 1,646.1 2 18 0 98774 100%
      9 1750 1750 104755 1,745.8 2 18 0 104755 100%
      9 1850 1850 110734 1,845.4 2 20 0 110734 100%
      9 1950 1910 113419 1,890.2 9 41855 0 113419 100%
      9 2050 1911 114437 1,907.1 2 77962 39 114397 99%
      9 2150 1911 114481 1,907.9 2 15 128 114353 99%
      9 2250 1911 114545 1,908.9 2 24 144 114401 99%

      4 workers, 61 contexts, accessing only one of them

      Nodes Sessions Ses.Active Samples samples/s mean resp. ms max resp. ms conn. errors valid samples %
      4 500 500 29796 496.6 6 52 0 29796 100%
      4 650 650 38706 645.0 7 149 0 38706 100%
      4 800 800 47585 793.0 8 129 0 47585 100%
      4 950 950 54467 907.7 43 377 0 54467 100%
      4 1100 1100 62500 1,041.6 54 396 0 62500 100%
      4 1250 1250 69446 1,157.3 81 512 0 69446 100%
      4 1400 1400 76217 1,270.2 97 517 0 76217 100%
      4 1550 1550 80216 1,336.8 152 810 0 80216 100%
      4 1700 1700 80797 1,346.5 271 864 0 80797 100%
      4 1850 1850 94172 1,569.3 182 822 0 94172 100%
      4 2000 1916 91014 1,516.8 253 48650 0 91014 100%
      4 2150 1916 95852 1,597.4 205 848 83 95769 99%

      4 workers, 1 context

      Nodes Sessions Ses.Active Samples samples/s mean resp. ms max resp. ms conn. errors valid samples %
      4 500 500 29922 498.7 2 39 0 29922 100%
      4 650 650 38923 648.7 1 39 0 38923 100%
      4 800 800 47916 798.5 1 17 0 47916 100%
      4 950 950 56896 948.2 1 17 0 56896 100%
      4 1100 1100 65889 1,098.1 1 115 0 65889 100%
      4 1250 1250 74874 1,247.8 1 101 0 74874 100%
      4 1400 1400 83818 1,396.8 1 17 0 83818 100%
      4 1550 1550 92830 1,547.0 1 17 0 92830 100%
      4 1700 1700 101805 1,696.6 1 11 0 101805 100%
      4 1850 1850 110785 1,846.3 1 11 0 110785 100%
      4 2000 1916 113747 1,895.6 10 53108 0 113747 100%
      4 2150 1916 114825 1,913.6 1 24 83 114742 99%

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          Bug - A problem that impairs or prevents the functions of the product. MODCLUSTER-388 Fix for MODCLUSTER-372 is broken

          • Blocker - To be worked above all other priorities. This term is chosen when the severity of the issue is very high, has no workaround, or the effort for the change is comparatively low. Issues that may be very publicly visible and could generate significant media attention may also drive a higher priority.
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              rhn-engineering-jclere Jean-Frederic Clere
              mbabacek1@redhat.com Michal Karm
              Michal Karm Michal Karm
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