Query-frontend slowdown on large responses

[pracucci]

Describe the bug
I'm investigating a query which took 12s to execute. According to the trace, it took 1.4s to execute the query in the querier (fetching chunks from ingesters + run PromQL engine) and most of the remaining time is spent in the query-frontend. The query result size is 70MB and I've the feeling the query-frontend may not be particularly performant on large query responses.

Expected behavior
A clear and concise description of what you expected to happen.

Storage Engine

• Blocks
• Chunks

But storage engine shouldn't matter in this issue.