apache/pinot

Increase the latency of a query which has TIME as sorted column when ORDER BY TIME DESC is applied

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#6,970 opened on May 25, 2021

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Description

Hi, There is usecase, where need to Increase the latency of a query which has ATIME as sorted column in a pinot table when ORDER BY ATIME DESC limit 100 is applied.

I've a select query which has ORDER BY ATIME ASC limit 100 is applied , then the the time taken for query is barely 15ms, (total rows - 450M, segments- 290, numOfDocsScanned - 318), where as for ORDER BY ATIME DESC limit 100 is taking around (timetaken -200ms, numDocsScanned - 5744955), which is very high, as it is reading whole segment.

Please provide a support reading the segment from bottom in this case, which can reduce the timetaken and numOfDocsScanned...

Thanks Akram Syed

Contributor guide

Research direction
Investigate the segment scan implementation in Pinot for ORDER BY DESC on a time column. Look into the QueryPlan and SegmentOperator classes to understand why ascending order scans are fast while descending scans are slow. Consider implementing a reverse scan or optimizing the existing scan to handle descending order efficiently.
Tech stack
java
Domain
database
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Java
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35