Goals

It is sometimes natural to want the "Top 5" and "Bottom 5" results. As someone coming from other databases, it seemed natural to run a single sorted query, then slice the beginning and end of the list.

Expected Results

The retrieval time of both chunks should be fast.

Actual Results

In reality, it seems like the end slice is doing a scan through the entire result set. I've worked around this by doing two queries with opposite sorts, but it was surprising behaviour to me.

Steps to Reproduce

Reproduction is here: https://github.com/thekevinbrown/realm-js-slow-writes

Code Sample

Reproduction is here: https://github.com/thekevinbrown/realm-js-slow-writes

Version of Realm and Tooling

• Realm JS SDK Version: 2.29.2
• Node or React Native: 0.59.10
• Client OS & Version: Android, Galaxy S9
• Which debugger for React Native: None, reproduced in release mode.

Note

This issue was originally raised as #2499, I'm splitting it out because multiple separate and unconnected issues were discovered in exploring there.