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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-1751) Perform aggregations, sorting, etc, in the preScannerNext instead of postScannerOpen
Date Thu, 19 Mar 2015 05:23:38 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-1751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14368534#comment-14368534
] 

Lars Hofhansl commented on PHOENIX-1751:
----------------------------------------

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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