sajjad-moradi commented on pull request #5705:
URL: https://github.com/apache/incubator-pinot/pull/5705#issuecomment-658860655
> An ECONNREFUSED situation (indicating that the remote server refused
connection) means that the pinot-server process on the server is not running.
> It will happen very quickly (the kernel will return the error), definitely
much quicker than any response from other requests for other servers. So, when
the broker gets notified of a connection request failure, it is likely the
first response seen in the map of responses.
>
> If the pinot-server process has gone down, then it is likely the case that
we have not gotten notification from Helix as yet (otherwise, we would have
taken down the server from the routing table and would not be routing to that
server).
>
> So, we are trying to address a window between the time the server went
down, and the time we get notified by Helix.
>
> True, Helix can sometimes take longer time to notify (depending on
zookeeper speed).
>
> It is good to note in the PR that this is the case we are addressing.
That's true. That's the issue that we faced and we want to prevent that, but
please note that we're catching not only connection refused exception but all
types of exceptions in `submitQuery()` and adding the exception stack trace to
the returned broker response will help debugging for other issues as well.
```java
for (Map.Entry<ServerRoutingInstance, InstanceRequest> entry :
requestMap.entrySet()) {
ServerRoutingInstance serverRoutingInstance = entry.getKey();
try {
_serverChannels.sendRequest(serverRoutingInstance, entry.getValue());
asyncQueryResponse.markRequestSubmitted(serverRoutingInstance);
} catch (Exception e) {
LOGGER.error("Caught exception while sending request {} to server:
{}, marking query failed", requestId,
serverRoutingInstance, e);
_brokerMetrics.addMeteredTableValue(rawTableName,
BrokerMeter.REQUEST_SEND_EXCEPTIONS, 1);
asyncQueryResponse.setBrokerRequestSendException(e);
asyncQueryResponse.markQueryFailed();
break;
}
}
```
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