[CASSANDRA-12915] SASI: Index intersection with an empty range really inefficient

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 3.11.0, 4.0-alpha1, 4.0
• Component/s: Feature/SASI
• Assignee: Corentin Chary
• Reporter: Corentin Chary

Authors

Corentin Chary

Reviewers

Alex Petrov

• Created: 16/Nov/16 07:50
• Updated: 15/May/20 08:03
• Resolved: 10/Mar/17 13:06

Description

It looks like RangeIntersectionIterator.java and be pretty inefficient in some cases. Let's take the following query:

SELECT data FROM table WHERE index1 = 'foo' AND index2 = 'bar';

In this case:

• index1 = 'foo' will match 2 items
• index2 = 'bar' will match ~300k items

On my setup, the query will take ~1 sec, most of the time being spent in disk.TokenTree.getTokenAt().

if I patch RangeIntersectionIterator so that it doesn't try to do the intersection (and effectively only use 'index1') the query will run in a few tenth of milliseconds.

I see multiple solutions for that:

• Add a static thresold to avoid the use of the index for the intersection when we know it will be slow. Probably when the range size factor is very small and the range size is big.
• CASSANDRA-10765

Issue Links

• is related to: CASSANDRA-10765 add RangeIterator interface and QueryPlan for SI
• links to: GitHub Pull Request #85