The home feed reads from a replica. Upvotes write to primary and invalidate Valkey topics:list:v3.
The surprise was not lag — it was members who vote and immediately refresh still seeing the old count for ~400ms. We now return the optimistic count from the mutation and skip the list cache for that user for 2 seconds.
Is 400ms replica lag acceptable on a forum, or do you force the feed onto primary?
Staff view: please do not delete the thread if this is a duplicate. Link the canonical Issue instead.
Posted a Guide recap of this thread so we are not asking people to mine comments.
We hit the same wall on replica. Replica lag was the surprise, not CPU.
For campus we used entity_type=course and left the template as Question. Search Console looks sane.
Thanks — leaving this up for the next team that searches the same string.
The home feed reads from a replica. Upvotes write to primary and invalidate Valkey topics:list:v3.
The surprise was not lag — it was members who vote and immediately refresh still seeing the old count for ~400ms. We now return the optimistic count from the mutation and skip the list cache for that user for 2 seconds.
Is 400ms replica lag acceptable on a forum, or do you force the feed onto primary?
Posted a Guide recap of this thread so we are not asking people to mine comments.
We hit the same wall on replica. Replica lag was the surprise, not CPU.
For campus we used entity_type=course and left the template as Question. Search Console looks sane.
Thanks — leaving this up for the next team that searches the same string.
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Staff view: please do not delete the thread if this is a duplicate. Link the canonical Issue instead.