Discrepancy in GA4 Session Counts – HyperLogLog in Blended Data?

Looker Q&A Looker Studio
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1

Hi everyone,

I’m seeing a discrepancy in session counts when using the GA4 connector in Looker Studio. Here’s what I’m noticing:

  1. Sessions in GA4 visualizations (direct from the GA4 connector) appear lower than expected, likely due to HyperLogLog approximation.
  2. However, when I create a blended data source using two instances of the same GA4 connector, the session count matches the raw value (instead of the approximated number).

My question:

  • Does HyperLogLog sampling not apply when blending GA4 data sources?
  • Is there any official documentation explaining how blending affects HyperLogLog calculations?
    Appreciate any insights or resources on this! Thanks.
2

@sam Could you assist here please?

3
  • "Does HyperLogLog sampling apply when blending GA4 data sources?
    Looker Studio doesn’t apply thresholds.
  • Is there any official documentation explaining how blending affects HyperLogLog calculations? I would appreciate any insights or resources on this. Thanks!
    If you want to learn more about ‘data blending,’ you can search for SQL Join, as it follows the same logic as Looker Studio’s data blending."