zbentley opened a new issue, #15703:
URL: https://github.com/apache/pulsar/issues/15703
**Describe the bug**
When the Python client calls `subscribe`, setting `receiver_queue_size` to a
value of 1 results in an effective receiver queue behavior of more than one;
Shared-type consumers with `receiver_queue_size=1` can "steal" messages that
other consumers could process.
**To Reproduce**
1. Create a persistent **non partitioned** topic.
2. Create a `Shared` subscription on the topic.
3. Publish 10 messages to the topic with sequential numeric payloads, e.g.
`message-0`, `message-1` and so on.
4. Create a consumer on the topic with the below code, and ensure it prints
`Press a key to acknowledge messages`.
5. In a second terminal, start another consumer on the topic with the below
code, and ensure it prints `Press a key to acknowledge messages`.
6. Press "enter" in the first consumer's terminal.
7. Observe that the first consumer processes **fewer than 9** messages (in
my tests it was usually 8, though I saw 6 occasionally; that might have been a
defect on my side though).
8. Press "enter" in the second consumer's terminal.
9. Observe that the second consumer processes **more than 1** message.
Consumer code:
```python
from pulsar import Client, ConsumerType, Timeout
import os
TOPIC = 'THETOPIC'
SUBSCRIPTION = 'THESUBSCRIPTION'
def recv(sub):
while True:
try:
msg = sub.receive(100)
print("Got message", msg.data())
return msg
except Timeout:
pass
def main():
client = Client(service_url='pulsar://localhost:6650')
sub = client.subscribe(
topic=TOPIC,
subscription_name=SUBSCRIPTION,
consumer_type=ConsumerType.Shared,
receiver_queue_size=1,
consumer_name=f'testconsumer-{os.getpid()}'
)
msg = recv(sub)
input("Press a key to acknowledge messages")
while True:
sub.acknowledge(msg)
msg = recv(sub)
if __name__ == '__main__':
main()
```
**Expected behavior**
The first consumer should process exactly 9 messages, every time. The second
consumer should process exactly 1 message, every time. The extra messages that
go to consumer 2 should go to consumer 1; otherwise, consumer 2 can "falsely
steal" those messages.
**Environment:**
Same environment as https://github.com/apache/pulsar/issues/15701
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