Thanks for the info Stephen. I was not aware that the pollSCM trigger was
ignored in a multibranch pipeline. Something is polling for changes. When
someone pushes a change, a build gets triggered shortly thereafter. I do
agree with you that polling is evil and not scalable with many branches. I
would like to make things event driven. Will need to investigate how with
git.
On Tuesday, August 29, 2017 at 5:33:42 PM UTC-5, Stephen Connolly wrote:
>
>
> On Tue 29 Aug 2017 at 23:21, Stephen Connolly <stephen.al...@gmail.com
> <javascript:>> wrote:
>
>>
>> On Tue 29 Aug 2017 at 22:35, Dallas Clement <dallas.a...@gmail.com
>> <javascript:>> wrote:
>>
>>> If I click on the "Scan Multibranch Pipeline Now" link in the Jenkins
>>> dashboard, it will kick off a build immediately even when there were no
>>> changes. I have my declarative Jenkinsfile configured to poll for SCM
>>> changes. I only want builds to be triggered from SCM changes. Any idea
>>> how I can suppress this behavior?
>>>
>>> pipeline {
>>> agent any
>>> options {
>>> disableConcurrentBuilds()
>>> timestamps()
>>> buildDiscarder(logRotator(numToKeepStr: '8'))
>>> }
>>> triggers {
>>> // Poll every 5 minutes for new changes
>>> pollSCM 'H/5 * * * *'
>>>
>>
>> You do know in multibranch that this poll is ignored?
>>
>
> To explain why the design is this way:
>
> 1. Polling is evil
>
> 2. In most SCM implementations the poll for each branch is effectively a
> redundant check, so if you have 10 branches all polling then Jenkins will
> end up doing the *exact same* operation in a parallel batch of 5 (default
> polling pool size) and follow up with another batch of 5... hammering the
> SCM where one request would provide the answer for all 10 branches.
>
> 3. Branch API needs to maintain its own state as to the last revision
> built. Polling will not update that correctly.
>
> 4. Polling for Git can be a mess due to how git can be configured to built
> multiple branches in one job.
>
> So the decision is that polling is disabled on multibranch leaf jobs (if
> you have a case where it is not disabled... congratulations you have found
> a bug... likely not the one you thought, but a bug... polling should not
> happen for leaf nodes of a multibranch project)
>
> You want to have indexing at a frequency such that if an event was lost,
> you cannot go more than this long without the build (typically somewhere
> between 4-24h for most people)
>
> You want event support to trigger the builds, not polling
>
>
>> }
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>>
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