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Add async as config option #31

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Add async as config option #31

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Andyandpandy Apr 13, 2023
ef090c8
Update src/main/java/org/apache/pulsar/logstash/outputs/Pulsar.java
Andyandpandy Jun 8, 2023
7b2f968
Update src/main/java/org/apache/pulsar/logstash/outputs/Pulsar.java
Andyandpandy Jun 8, 2023
882ff02
Update README.md
Andyandpandy Jun 8, 2023
7c1bc75
Update README.md
Andyandpandy Jun 8, 2023
2fb1f80
Update send function to also include s as param to avoid runtime errors
Andyandpandy Jun 8, 2023
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9 changes: 9 additions & 0 deletions README.md
View file
Original file line number Diff line number Diff line change
@@ -31,6 +31,15 @@ This plugin supports these configuration options.
| ciphers | array, ciphers list | No |
| enable_token | boolean, one of [true, false]. default is false | No |
| auth_plugin_params_String | string | No |
| enable_async | boolean, one of [true, false]. default is false | No |


## Sync vs Async

Sync is slower because it requires verification that a message is received. Sync supports exactly/effectively once messaging. This means there is a big network latency increase here.

Async is faster because it sends messages out and doesn't care if the message was received/processed or not. Async should only be used if you want "at most once" messaging and don't care if messages are lost.

# Example
pulsar without tls & token
```
23 changes: 20 additions & 3 deletions src/main/java/org/apache/pulsar/logstash/outputs/Pulsar.java
View file
Original file line number Diff line number Diff line change
@@ -97,6 +97,9 @@ public class Pulsar implements Output {
private static final PluginConfigSpec<String> CONFIG_AUTH_PLUGIN_PARAMS_STRING =
PluginConfigSpec.stringSetting("auth_plugin_params_String","");

private static final PluginConfigSpec<Boolean> CONFIG_ENABLE_ASYNC =
PluginConfigSpec.booleanSetting("enable_async",false);

private final CountDownLatch done = new CountDownLatch(1);

private final String producerName;
@@ -125,6 +128,9 @@ public class Pulsar implements Output {
//Token
private final boolean enableToken;

// Sends messages async if set, otherwise sync
private final boolean enableAsync;

// TODO: batchingMaxPublishDelay milliseconds

// TODO: sendTimeoutMs milliseconds 30000
@@ -148,6 +154,7 @@ public Pulsar(final String id, final Configuration configuration, final Context

enableTls = configuration.get(CONFIG_ENABLE_TLS);
enableToken = configuration.get(CONFIG_ENABLE_TOKEN);
enableAsync = configuration.get(CONFIG_ENABLE_ASYNC);

try {
if(enableTls && enableToken){
@@ -222,15 +229,25 @@ public void output(final Collection<Event> events) {
codec.encode(event, baos);
String s = baos.toString();
logger.debug("topic is {}, message is {}", eventTopic, s);
getProducer(eventTopic).newMessage()
.value(s.getBytes())
.sendAsync();
send(eventTopic, s);
} catch (Exception e) {
logger.error("fail to send message", e);
}
}
}

private void send(String topic, String s){
if (enableAsync){
getProducer(topic).newMessage()
.value(s.getBytes())
.sendAsync();
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We still need to add a callback to print a log when failing to publish messages.

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This send function is only called inside a try/catch, where it logs "fail to send message" with the exception. See line 225-235.

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@RobertIndie RobertIndie Jun 21, 2023 •
edited
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It won't catch the exception thrown from sendAsync. We need to use CompletableFuture.exceptionally to catch it. Please see: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html#exceptionally-java.util.function.Function-

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Okay.. Am I reading this right?

CompletableFuture.exceptionally description:

Returns a new CompletableFuture that is completed when this CompletableFuture completes, with the result of the given function of the exception triggering this CompletableFuture's completion when it completes exceptionally; otherwise, if this CompletableFuture completes normally, then the returned CompletableFuture also completes normally with the same value.

This doesn't throw a custom Exception that inherits from the class Exception as usual? I don't think I understand what this is describing. I'm trying to decipher it, but does it mean that it returns the function that triggered an Exception rather than actually throwing the Exception. In that case I guess I couldn't try/catch? Or does it mean that I am supposed to just provide a function that is throwable, so when CompletableFuture throws, it triggers my function with where it failed?

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@RobertIndie RobertIndie Jul 5, 2023 •
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Sorry for the late reply.

The sendAsync will not throw any exceptions. The producer already catches all the exceptions and places them into the Future. You could check the code here.

Therefore if there are any exceptions thrown in the send operation, the function fn in the exceptionally will be called. And I think we need to print the error log in that function.

Or does it mean that I am supposed to just provide a function that is throwable, so when CompletableFuture throws, it triggers my function with where it failed?

That's correct.

However, you still need to use try/catch here, because we couldn't guarantee that this code won't throw the exception:

getProducer(topic).newMessage()
                .value(s.getBytes())
                .sendAsync();

}else {
getProducer(topic).newMessage()
.value(s.getBytes())
.send();
}
}

private org.apache.pulsar.client.api.Producer<byte[]> getProducer(String topic) throws PulsarClientException {

if(producerMap.containsKey(topic)){