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https://issues.apache.org/jira/browse/HBASE-11667?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14085931#comment-14085931
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Lars Hofhansl commented on HBASE-11667:
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bq. It's suspicious that the client relies on the server telling it state it
could track locally (or am I missing something?).
The client cannot track what the server is doing unless the server tells it
what it did (i.e. how far it got with its scan). I don't think we can recover
if there is no way to know which state to recover to.
All the client can know without help from the server (this particular scan) if
last startkey of the last region. I tried to only use that information, but it
turns out that does not work. Interesting problem :)
> Comment ClientScanner logic for NSREs.
> --------------------------------------
>
> Key: HBASE-11667
> URL: https://issues.apache.org/jira/browse/HBASE-11667
> Project: HBase
> Issue Type: Improvement
> Reporter: Lars Hofhansl
> Assignee: Lars Hofhansl
> Priority: Minor
> Fix For: 0.99.0, 2.0.0, 0.94.23, 0.98.6
>
> Attachments: 11667-0.94.txt, 11667-doc-0.94.txt, 11667-trunk.txt,
> HBASE-11667-0.98.patch, IntegrationTestBigLinkedListWithRegionMovement.patch
>
>
> We ran into an issue with Phoenix where a RegionObserver coprocessor
> intercepts a scan and returns an aggregate (in this case a count) with a fake
> row key. It turns out this does not work when the {{ClientScanner}}
> encounters NSREs, as it uses the last key it saw to reset the scanner to try
> again (which in this case would be the fake key).
> While this is arguably a rare case and one could also argue that a region
> observer just shouldn't do this... While looking at {{ClientScanner}}'s code
> I found this logic not necessary.
> A NSRE occurred because we contacted a region server with a key that it no
> longer hosts. This is the start key, so it is always correct to retry with
> this same key. That simplifies the ClientScanner logic and also make this
> sort of coprocessors possible,
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