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https://issues.apache.org/jira/browse/PHOENIX-1751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14368534#comment-14368534
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Lars Hofhansl commented on PHOENIX-1751:
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And even than, that would break coprocessor chaining, if the Phoenix one is not
last one in the chain (the RegionObserver itself cannot have any state, so the
state needs to be in the RegionScanner, but a later coprocessor in the chain
might return another instance that wraps or replaces the passed one).
> Perform aggregations, sorting, etc, in the preScannerNext instead of
> postScannerOpen
> ------------------------------------------------------------------------------------
>
> Key: PHOENIX-1751
> URL: https://issues.apache.org/jira/browse/PHOENIX-1751
> Project: Phoenix
> Issue Type: Bug
> Reporter: Lars Hofhansl
>
> HBase retains a lease for every scanner. Then lease expires the scan will no
> longer (be allowed to) work. The leases guard against the client going away,
> and allow cleaning up resources if that happens.
> At various points HBase "suspends" the lease while the region server are
> working on behalf of this scanner, so that the lease won't expire even though
> the server is working on it.
> HBase does that during the scanning process. Crucially it suspends the leaser
> after the scanner is opened, before next() is issued on it.
> The outcome of all this is that Phoenix executes aggregates, sorts, etc, with
> the lease in place, and hence if these take a bit the lease can expire even
> though the server was working on it.
> Phoenix should do this work in preScannerNext, being careful that the
> precalculation is only performed once.
> I'll attach a sample patch soon.
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