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https://issues.apache.org/jira/browse/TS-2384?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13831241#comment-13831241
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Vladyslav Bachynskyi commented on TS-2384:
------------------------------------------

Sure!

> Regression in key-lookup code between 4.0.x and 4.1.x
> -----------------------------------------------------
>
>                 Key: TS-2384
>                 URL: https://issues.apache.org/jira/browse/TS-2384
>             Project: Traffic Server
>          Issue Type: Bug
>          Components: Cache
>            Reporter: Igor Galić
>             Fix For: 4.2.0
>
>
> As reported on users@
> {noformat}
> ATS 4.0.1
> Volume  #1 - store='/dev/sda'
> first key       409542BD429764BEE60B0610B8924C4D
> key     6BA7E5696E9A9E7A1E05212E5264D3C4
> sync_serial     10836
> write_serial    388912
> header length   2480
> fragment type   1
> No of Alternates        1
> {noformat}
> {noformat}
> ATS 4.1.1
> Volume  #1 - store='/dev/sda'
> first key       409542BD429764BEE60B0610B8924C4D
> key     34CEA58AC5FBA6D240C484307DE4C315
> sync_serial     10837
> write_serial    388912
> header length   2480 
> fragment type   1    
> No of Alternates        1
> {noformat}
> When run 4.1.1 all previously cached objects under 4.0.1 are MISS, these 
> objects  downloading from parent, and then they HIT again.
> *Note* This does not cause the cache to be reinitialized.
> It's just that the generated cache-lookup *key* is wrong in 4.1.x. This means 
> that the existing objects on the disks will stay in place, but we won't be 
> able to find them, because we are looking in the wrong place. As such we 
> simply store the object again.
> That's *almost* the same for people running with a 60 TiB cache, because 
> everything requested is also stored again,
> and after a while the old objects that have been lying around for a while 
> will be rotated out so that's bad. People with
> tiny caches or very high turn overs might even notice the downward spike in 
> 304s.



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