# Why is Jenkins so slow processing backlog queue? **URL:** \ **Category:** Ask a question\ **Created:** [January 28, 2026, 1:02pm UTC](https://community.jenkins.io/t/why-is-jenkins-so-slow-processing-backlog-queue/36107 "2026-01-28T13:02:56Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![saper](https://dub1.discourse-cdn.com/flex013/user_avatar/community.jenkins.io/saper/32/138_2.png) [@saper](https://community.jenkins.io/u/saper)\ **Post date:** [January 28, 2026, 1:02pm UTC](https://community.jenkins.io/t/why-is-jenkins-so-slow-processing-backlog-queue/36107/1 "2026-01-28T13:02:56Z")
Jenkins setup: We are running Jenkins 2.528.3 The job in question runs on a single static worker with 1 executor (due to hardware required only 1 job can run in parallel) The job is a declarative pipeline We in the past weeks we have observer the same scenario at least 3 times: 1. The worker goes down (disk space problem) 2. Build queue of externally triggered items grows (up to say 4000) 3. The worker comes back 4. Jenkins is extremely slow processing the back log The following observations have been made: 1. Even if a job completes on a worker (with status SUCCESS or FAILURE) it remains visible on the /computer/WORKER and it takes a long time to get another job scheduled. 2. There is no thread dump that can be taken on such job 3. When we query the queue it seems to decrease slowly: ```auto jq '.items[]."_class"' | uniq -c 583 "hudson.model.Queue$BlockedItem" 3173 "hudson.model.Queue$BuildableItem" ``` 21 minutes later: ```auto jq '.items[]."_class"' | uniq -c 355 "hudson.model.Queue$BlockedItem" 3169 "hudson.model.Queue$BuildableItem" ``` 1. The following messages flood the Jenkins log: ```auto Jan 28 13:09:15 vm2611 jenkins[371907]: 2026-01-28 12:09:15.594+0000 [id=904361] WARNING o.j.p.w.s.s.ExecutorStepExecution$PlaceholderTask#getCau seOfBlockage: Refusing to build ExecutorStepExecution.PlaceholderTask{label=worker-label,context=CpsStepContext[3:node]:ourjob/6#84013} and going to cancel it, even thoug h it was supposedly stopped already, because associated build is complete ``` 1. We have also seen the following messages (not coming very often) ```auto Jan 28 12:39:06 vm2611 jenkins[371907]: 2026-01-28 11:39:06.802+0000 [id=902454] WARNING o.j.p.w.cps.CpsThreadGroup#saveProgramIfPossible: progra m state save failed Jan 28 12:39:06 vm2611 jenkins[371907]: java.nio.channels.ClosedByInterruptException Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/java.nio.channels.spi.AbstractInterruptibleChannel.end(AbstractInterruptibleChannel.java:200) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/sun.nio.ch.FileChannelImpl.endBlocking(FileChannelImpl.java:172) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/sun.nio.ch.FileChannelImpl.write(FileChannelImpl.java:309) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-support//org.jenkinsci.plugins.workflow.support.pickles.serialization.RiverWriter.(RiverWriter.java:109) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.saveProgram(CpsThreadGroup.java:638) Jan 28 12:39:06 vm2611 jenkins[371907]: Caused: java.io.IOException: Failed to persist /var/lib/jenkins/jobs/ourjob/jobs/6/builds/84806/program.dat Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.saveProgram(CpsThreadGroup.java:652) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.saveProgram(CpsThreadGroup.java:613) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.saveProgramIfPossible(CpsThreadGroup.java:596) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:520) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:372) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:302) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService.lambda$wrap$4(CpsVmExecutorService.java:143) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317) Jan 28 12:39:06 vm2611 jenkins[371907]: at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:139) Jan 28 12:39:06 vm2611 jenkins[371907]: at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28) Jan 28 12:39:06 vm2611 jenkins[371907]: at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:68) Jan 28 12:39:06 vm2611 jenkins[371907]: at jenkins.util.ErrorLoggingExecutorService.lambda$wrap$0(ErrorLoggingExecutorService.java:51) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144) Jan 28 12:39:06 vm2611 jenkins[371907]: at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$1.call(CpsVmExecutorService.java:53) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$1.call(CpsVmExecutorService.java:50) Jan 28 12:39:06 vm2611 jenkins[371907]: at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:136) Jan 28 12:39:06 vm2611 jenkins[371907]: at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:275) Jan 28 12:39:06 vm2611 jenkins[371907]: at PluginClassLoader for workflow-cps//org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService.lambda$categoryThreadFactory$0(CpsVmExecutorService.java:50) ``` I do not expect anyone to troubleshoot this for us, but there is something I’d like to understand what is the logic of the queue processing, why is it so slow and how are “blocked items” created and killed? ---
**Author:** ![saper](https://dub1.discourse-cdn.com/flex013/user_avatar/community.jenkins.io/saper/32/138_2.png) [@saper](https://community.jenkins.io/u/saper)\ **Post date:** [January 29, 2026, 12:26pm UTC](https://community.jenkins.io/t/why-is-jenkins-so-slow-processing-backlog-queue/36107/2 "2026-01-29T12:26:45Z")
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