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  1. Jenkins
  2. JENKINS-65308

Jenkins.trimLabels gets increasingly slower as number of nodes and labels increase

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    Details

    • Type: Bug
    • Status: Closed (View Workflow)
    • Priority: Major
    • Resolution: Fixed
    • Component/s: core
    • Environment:
    • Similar Issues:
    • Released As:
      2.288 - Apr 13, 2021, 2.289 - Apr 20, 2021

      Description

      We've been trying to track down some issues we've been seeing around Queue lock
      contention on one of our Jenkins clusters. The lock contention manifests in
      both UI instability/slowness and failures with REST API calls to add, update or
      remove nodes. We use the Swarm plugin on the primary and swarm-client (version
      3.24) on the agents to connect to the primary. The REST API failures aren't due
      to exceptions from Jenkins, but to the API calls exceeding the configured
      proxy_read_timeout (180s) for the nginx instance we have in front of Jenkins.
      That manifests in the swarm-client process on the agents receiving a 504 from
      nginx since Jenkins didn't respond in time.

      Thread dumps gathered during periods of instability show that hundreds of
      threads are waiting for the Queue lock to be able to add, update or remove
      a node.

      "Handling POST /plugin/swarm/createSlave from 10.224.1.234 : Jetty (winstone)-1218487" #1218487 prio=5 os_prio=0 tid=0x00007f4732c7f800 nid=0x2f96 waiting on condition [0x00007f3c6b5f2000]
         java.lang.Thread.State: WAITING (parking)
             at sun.misc.Unsafe.park(Native Method)
             - parking to wait for  <0x00007f3f117ca288> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
             at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
             at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
             at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
             at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
             at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
             at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
             at hudson.model.Queue._withLock(Queue.java:1441)
      [snip..]
      

      The vast majority of the time, the thread holding the Queue lock during each
      thread dump is performing operations within the Jenkins.trimLabels method as
      part of adding, updating or removing a node.

      "Handling POST /plugin/swarm/createSlave from 10.240.81.215 : Jetty (winstone)-1218362" #1218362 prio=5 os_prio=0 tid=0x00007f47265fd000 nid=0x2e11 runnable [0x00007f3c85ceb000]
         java.lang.Thread.State: RUNNABLE
              at hudson.util.QuotedStringTokenizer.hasMoreTokens(QuotedStringTokenizer.java:184)
              at hudson.model.Label.parse(Label.java:585)
              at hudson.model.Node.getAssignedLabels(Node.java:303)
              at hudson.model.Label.matches(Label.java:196)
              at hudson.model.Label.getNodes(Label.java:233)
              at hudson.model.Label.isEmpty(Label.java:430)
              at jenkins.model.Jenkins.trimLabels(Jenkins.java:2201)
              at jenkins.model.Nodes$4.call(Nodes.java:214)
              at jenkins.model.Nodes$4.call(Nodes.java:210)
              at hudson.model.Queue._withLock(Queue.java:1443)
              at hudson.model.Queue.withLock(Queue.java:1304)
              at jenkins.model.Nodes.updateNode(Nodes.java:210)
              at jenkins.model.Jenkins.updateNode(Jenkins.java:2176)
              at hudson.model.Node.save(Node.java:139)
              at hudson.model.Node.setTemporaryOfflineCause(Node.java:274)
              at hudson.model.Computer.setNode(Computer.java:820)
              at hudson.slaves.SlaveComputer.setNode(SlaveComputer.java:895)
              at hudson.model.AbstractCIBase.updateComputer(AbstractCIBase.java:137)
              at hudson.model.AbstractCIBase.access$000(AbstractCIBase.java:43)
              at hudson.model.AbstractCIBase$2.run(AbstractCIBase.java:223)
              at hudson.model.Queue._withLock(Queue.java:1384)
              at hudson.model.Queue.withLock(Queue.java:1261)
              at hudson.model.AbstractCIBase.updateComputerList(AbstractCIBase.java:206)
              at jenkins.model.Jenkins.updateComputerList(Jenkins.java:1632)
              at jenkins.model.Nodes$2.run(Nodes.java:151)
              at hudson.model.Queue._withLock(Queue.java:1384)
              at hudson.model.Queue.withLock(Queue.java:1261)
              at jenkins.model.Nodes.addNode(Nodes.java:147)
              at jenkins.model.Jenkins.addNode(Jenkins.java:2155)
              at hudson.plugins.swarm.PluginImpl.doCreateSlave(PluginImpl.java:224)
      

      I've attached a couple of archives created using the collectPerformanceData
      script that contain the relevant thread dumps.

      During the aforementioned periods of instability there are between 1500-1600
      unique labels and 400-500 workers, as gathered from the script console using
      Jenkins.instance.labels.size() and Jenkins.instance.nodes.size().

      I'm able to replicate the increasing slowness using Groovy scripts that mirror
      what our worker creation steps look like. I've attached both scripts.
      create-workers.groovy creates the workers, remove-workers.groovy removes
      them. To make it match our swarm-client workflow we create SwarmSlave agents
      in the script but that detail probably doesn't matter for reproduction
      purposes.

      Creating and then removing workers with a single label is fast, as you'd
      expect. Here's some snipped output for creation (full output attached as create-workers-single-label.log):

      ...
      uniqueLabels: 395 nodes: 393 swarm-test-392: 63ms
      uniqueLabels: 396 nodes: 394 swarm-test-393: 65ms
      uniqueLabels: 397 nodes: 395 swarm-test-394: 87ms
      uniqueLabels: 398 nodes: 396 swarm-test-395: 62ms
      uniqueLabels: 399 nodes: 397 swarm-test-396: 62ms
      uniqueLabels: 400 nodes: 398 swarm-test-397: 62ms
      uniqueLabels: 401 nodes: 399 swarm-test-398: 63ms
      uniqueLabels: 402 nodes: 400 swarm-test-399: 63ms
      uniqueLabels: 403 nodes: 401 swarm-test-400: 64ms
      Total time to create 400 workers: 9183ms
      

      And then the same for removal (full output attached as remove-workers-single-label.log):

      ...
      uniqueLabels: 10 nodes: 8 swarm-test-91: 0ms
      uniqueLabels: 9 nodes: 7 swarm-test-92: 0ms
      uniqueLabels: 8 nodes: 6 swarm-test-93: 1ms
      uniqueLabels: 7 nodes: 5 swarm-test-94: 0ms
      uniqueLabels: 6 nodes: 4 swarm-test-95: 1ms
      uniqueLabels: 5 nodes: 3 swarm-test-96: 0ms
      uniqueLabels: 4 nodes: 2 swarm-test-97: 1ms
      uniqueLabels: 3 nodes: 1 swarm-test-98: 0ms
      uniqueLabels: 1 nodes: 0 swarm-test-99: 1ms
      Total time to remove 401 workers: 8675ms
      

      But once you start adding more labels, thing start slowing down drastically.
      Here's some snipped output for creation (full output attached as create-workers-multiple-labels.log):

      ...
      uniqueLabels: 809 nodes: 393 swarm-test-392: 1875ms
      uniqueLabels: 811 nodes: 394 swarm-test-393: 1875ms
      uniqueLabels: 813 nodes: 395 swarm-test-394: 1883ms
      uniqueLabels: 815 nodes: 396 swarm-test-395: 1888ms
      uniqueLabels: 817 nodes: 397 swarm-test-396: 1901ms
      uniqueLabels: 819 nodes: 398 swarm-test-397: 1913ms
      uniqueLabels: 821 nodes: 399 swarm-test-398: 1915ms
      uniqueLabels: 823 nodes: 400 swarm-test-399: 1927ms
      uniqueLabels: 825 nodes: 401 swarm-test-400: 1939ms
      Total time to create 400 workers: 261866ms
      

      And then the same for removal (full output attached as remove-workers-multiple-labels.log):

      ...
      uniqueLabels: 39 nodes: 8 swarm-test-91: 3ms
      uniqueLabels: 37 nodes: 7 swarm-test-92: 2ms
      uniqueLabels: 35 nodes: 6 swarm-test-93: 2ms
      uniqueLabels: 33 nodes: 5 swarm-test-94: 1ms
      uniqueLabels: 31 nodes: 4 swarm-test-95: 1ms
      uniqueLabels: 29 nodes: 3 swarm-test-96: 0ms
      uniqueLabels: 27 nodes: 2 swarm-test-97: 0ms
      uniqueLabels: 25 nodes: 1 swarm-test-98: 1ms
      uniqueLabels: 1 nodes: 0 swarm-test-99: 0ms
      Total time to remove 401 workers: 258555ms
      

      Increasing (roughly doubling it in this case) the number of unique labels makes
      the same process that originally took about 9s for each operation take about
      4 minutes and 20 seconds for each operation.

      Is there some way to make Jenkins.trimLabels less expensive even in the
      face of thousands of labels and hundreds of workers? To my eye it looks like
      the current code path has several nested loops (outer loop over every label,
      inner loop over every worker, inner loop over every parsed token from the label
      tokenizer, inner loop over every char in the raw label str) which are what
      contribute to the increase in execution time as the inputs get larger.

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            Hide
            fatmcgav Gavin Williams added a comment -

            Thanks for the detail both

            Show
            fatmcgav Gavin Williams added a comment - Thanks for the detail both
            Hide
            bmunoz Beatriz Muñoz added a comment -

            Hey Gavin. What Raihaan said is correct. Here the discussion

            Show
            bmunoz Beatriz Muñoz added a comment - Hey Gavin. What Raihaan said is correct.  Here the discussion
            Hide
            raihaan Raihaan Shouhell added a comment -

            Hey Gavin, it was rejected because the change has not been in weekly releases for long and it is not a regression. Thus it was decided that it be left out because this change poses a risk of a regression. So yes it will not be in 2.277.4, it will likely be in the LTS after that whose baseline is likely to be 2.289.

            Show
            raihaan Raihaan Shouhell added a comment - Hey Gavin, it was rejected because the change has not been in weekly releases for long and it is not a regression. Thus it was decided that it be left out because this change poses a risk of a regression. So yes it will not be in 2.277.4, it will likely be in the LTS after that whose baseline is likely to be 2.289.
            Hide
            fatmcgav Gavin Williams added a comment -

            Hi Beatriz Muñoz

            I just noticed that this issue has been labelled as `2.277.4-rejected`.

            Does that mean it's not going to be part of the next LTS release?

            Could you elaborate on the reasoning behind that? From our testing and production usage thus far, this change has a massive benefit on overall Jenkins performance, especially when runnings hundreds of connected agents that are being dynamically created...

            Thanks

            Show
            fatmcgav Gavin Williams added a comment - Hi Beatriz Muñoz I just noticed that this issue has been labelled as `2.277.4-rejected`. Does that mean it's not going to be part of the next LTS release? Could you elaborate on the reasoning behind that? From our testing and production usage thus far, this change has a massive benefit on overall Jenkins performance, especially when runnings hundreds of connected agents that are being dynamically created... Thanks
            Hide
            raihaan Raihaan Shouhell added a comment -

            Hey Gavin, thanks to both you and Jonah that this was able to be resolved so quickly. The initial investigation done was superb which allowed me to focus on the issue. Its collaboration like this that helps issues get resolved quickly.

            Show
            raihaan Raihaan Shouhell added a comment - Hey Gavin, thanks to both you and Jonah that this was able to be resolved so quickly. The initial investigation done was superb which allowed me to focus on the issue. Its collaboration like this that helps issues get resolved quickly.

              People

              Assignee:
              raihaan Raihaan Shouhell
              Reporter:
              jonahbull Jonah Bull
              Votes:
              3 Vote for this issue
              Watchers:
              8 Start watching this issue

                Dates

                Created:
                Updated:
                Resolved: