[BUG] Same task received/processed by more than one worker about asynq HOT 4 CLOSED

Thanks for filing this bug report!

I ran the same code on my machine with 4 worker processes reading from the same redis instance but could not reproduce the bug.

It could be that you've run the client code multiple times and there were duplicate tasks in Redis. Would you mind trying this again with clean Redis DB?

You can asynqmon stats to make sure that there's no tasks in Redis.
You can flush redis by running redis-cli flushdb

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@hibiken I prepared an environment where this can be reproduced (uses docker, docker-compose):
https://github.com/hibiken/asynq/compare/master...gunnsth:issue90-reproduce?expand=1
to reproduce it:

$ cd testdata
$ docker-compose up

It will not always give exactly the same results, I guess there's some stochastic/random factor that determines which taskrunner catches tasks.

Example outputs:

taskrunner_1   | Tasks processed
taskrunner_1   | (map[int]int) (len=5) {
taskrunner_1   |  (int) 10: (int) 1,
taskrunner_1   |  (int) 2: (int) 1,
taskrunner_1   |  (int) 4: (int) 1,
taskrunner_1   |  (int) 6: (int) 1,
taskrunner_1   |  (int) 8: (int) 1
taskrunner_1   | }
taskrunner3_1  | Tasks processed
taskrunner3_1  | (map[int]int) (len=3) {
taskrunner3_1  |  (int) 1: (int) 1,
taskrunner3_1  |  (int) 2: (int) 1,
taskrunner3_1  |  (int) 20: (int) 1
taskrunner3_1  | }
taskrunner2_1  | Tasks processed
taskrunner2_1  | (map[int]int) (len=7) {
taskrunner2_1  |  (int) 1: (int) 1,
taskrunner2_1  |  (int) 3: (int) 1,
taskrunner2_1  |  (int) 5: (int) 1,
taskrunner2_1  |  (int) 7: (int) 1,
taskrunner2_1  |  (int) 9: (int) 1,
taskrunner2_1  |  (int) 11: (int) 1,
taskrunner2_1  |  (int) 14: (int) 1
taskrunner2_1  | }

We see that both taskrunner1 and 3 have processed task 2. And taskrunner3 and 2 have both processed task1.

Is there any way we can ensure that this does not happen?
There should not be any duplicate tasks since this creates a fresh redis instance.
(to be sure, it's easy to clean all the docker images).

Would it be possible to clear all tasks prior to start creating tasks (programmatically)? Just to make sure?

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@gunnsth
Could you try adding this to your taskqueue.go to flush DB to start from clean slate?

import "github.com/go-redis/redis/v7"

func main() {
    // Flush DB first to start from a clean slate.
    rdb := redis.NewClient(&redis.Options{
       Addr: "redis:6379",
       Password: "xxxx",
    })
    if err := rdb.FlushDB().Err(); err != nil {
        log.Fatalln(err)
    }
 
    // ... create asynq.Client and schedule tasks (your existing code)
}

Let me know if you are still seeing duplicate tasks.
Otherwise, we can close this issue 👍

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@gunnsth I finally figured out what's causing this. Fix is in #170

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