[CASSANDRA-13794] Fix short read protection logic for querying more rows

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 3.0.15, 3.11.1
• Component/s: Legacy/Coordination
• Labels: Correctness
• Severity: Normal
• Assignee: Aleksey Yeschenko
• Reporter: Benedict Elliott Smith

Authors

Aleksey Yeschenko

Reviewers

Benedict Elliott Smith

• Created: 24/Aug/17 12:36
• Updated: 16/Apr/19 09:30
• Resolved: 20/Sep/17 16:59

Description

Discovered by Benedict Elliott Smith while reviewing CASSANDRA-13747:

While reviewing I got a little suspicious of the modified line DataResolver :479, as it seemed that n and x were the wrong way around... and, reading the comment of intent directly above, and reproducing the calculation, they are indeed.

This is probably a significant enough bug that it warrants its own ticket for record keeping, though I'm fairly agnostic on that decision.

I'm a little concerned about our current short read behaviour, as right now it seems we should be requesting exactly one row, for any size of under-read, which could mean extremely poor performance in case of large under-reads.

I would suggest that the outer unconditional Math.max is a bad idea, has been (poorly) insulating us from this error, and that we should first be asserting that the calculation yields a value >= 0 before setting to 1.

Issue Links

• is related to: CASSANDRA-13747 Fix AssertionError in short read protection