Lars Hofhansl created PHOENIX-1751:
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Summary: 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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