[PHOENIX-1751] Perform aggregations, sorting, etc, in the preScannerNext instead of postScannerOpen

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Assignee: Lars Hofhansl
• Reporter: Lars Hofhansl
• Created: 19/Mar/15 04:50
• Updated: 25/Aug/16 18:35
• Resolved: 25/Aug/16 18:35

Description

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.