[KAFKA-10459] Document IQ APIs where order does not hold between stores

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.7.0
• Component/s: streams
• Assignee: Luke Chen
• Reporter: Jorge Esteban Quilcate Otoya
• Created: 03/Sep/20 08:43
• Updated: 23/Sep/20 04:46
• Resolved: 22/Sep/20 01:41

Description

From https://github.com/apache/kafka/pull/9138#discussion_r480469688 :
 

This is out of the scope of this PR, but I'd like to point out that the current IQ does not actually obey the ordering when there are multiple local stores hosted on that instance. For example, if there are two stores from two tasks hosting keys {1, 3} and {2,4}, then a range query of key [1,4] would return in the order of 1,3,2,4 but not 1,2,3,4 since it is looping over the stores only. This would be the case for either forward or backward fetches on range-key-range-time.

For single key time range fetch, or course, there's no such issue.

I think it worth documenting this for now until we have a fix (and actually we are going to propose something soon).

Issue Links

• links to: GitHub Pull Request #9251