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Common reasons Firestore queries feel slow:

  1. Missing Indexes
    Composite queries require indexes. Firestore will show an error with a link to create one.

  2. Large documents
    Firestore charges & loads by document size. Try splitting into multiple small documents.

  3. Unoptimized structure
    Don’t nest deep maps. Instead, keep data flat.

  4. Cold start
    The first query is always slower; subsequent ones use cached results.

Use orderBy() with indexed fields for best results.

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  • Is there a question or is this post ment as a kind of HowTo? Commented Nov 26 at 8:19
  • Title of the question is "Why my (...) query so slow, (...)", so you should've show your query, not some random quotes (or possibly, LLM output). Commented Nov 26 at 9:03
  • Even small datasets can be slow if queries aren’t optimized. Firestore requires proper indexing—single-field indexes are automatic, but compound queries need composite indexes. Large documents, client-side filtering, and unnecessary reads add latency. Use .select() to fetch only needed fields, ensure server-side filters, and check network conditions. Avoid not-in, array-contains-any, or unindexed orderBy for better performance. Commented Nov 27 at 4:27
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