TLDR Tech / Practical
ClickHouse Addresses 32ms Tail Latency on High-RTT Networks
ClickHouse engineers investigated a 32 ms tail latency issue affecting simple SELECT queries after periods of inactivity on networks with high round-trip times. They identified that unbatched metadata packets, sent concurrently with result data, rapidly depleted the TCP congestion window once it had been reset. The solution involved implementing application-level batching for these metadata packets, which reduced the number of TCP segments by half and eliminated the tail latency problem.
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