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Yanqi Lv authored
I'm testing the performance of Pub/Sub command recently. I find if many clients unsubscribe or are killed simultaneously, Redis needs a long time to deal with it. In my experiment, I set 5000 clients and each client subscribes 100 channels. Then I call `client kill type pubsub` to simulate the situation where clients unsubscribe all channels at the same time and calculate the execution time. The result shows that it takes about 23s. I use the _perf_ and find that `listSearchKey` in `pubsubUnsubscribeChannel` costs more than 90% cpu time. I think we can optimize this situation. In this PR, I replace list with dict to track the clients subscribing the channel more efficiently. It changes O(N) to O(1) in the search phase. Then I repeat the experiment as above. The results are as follows. | | Execution Time(s) |used_memory(MB) | | :---------------- | :------: | :----: | | unstable(1bd0b549) | 23.734 | 65.41 | | optimize-pubsub | 0.288 | 67.66 | Thanks for #11595 , I use a no-value dict and the results shows that the performance improves significantly but the memory usage only increases slightly. Notice: - This PR will cause the performance degradation about 20% in `[p|s]subscribe` command but won't freeze Redis.
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