A skewed SingleStore shard key turns queries into full scatter-gather
Shows how to fix a skewed SingleStore shard key turns queries into full scatter-gather. Use it when you hit this exact problem. Skip it when your error message or symptom looks different.
TL;DR
Run EXPLAIN on your hot queries: if you see Gather partitions:all on queries that should hit one partition, the shard key is wrong. Pick the least restrictive shard key that still avoids skew.
Steps
- Pick the least restrictive shard key that still avoids skew. Run EXPLAIN on your hot queries: if you see Gather partitions:all on queries that should hit one partition, the shard key is wrong. For time-series or URL-like data, a composite key of the high-cardinality filter plus a second column usually beats a single skewed column. Review the whole table layout with the Optimizing Table Data Structures guide when this pattern repeats.
When to use
You are seeing this: For time-series or URL-like data, a composite key of the high-cardinality filter plus a second column usually beats a single skewed column. Use this skill when you run into "A skewed SingleStore shard key turns queries into full scatter-gather".
When not to use
If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.
Versions
No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.
Why this happens
The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.