I've looked over the documentation for Google's PubSub, and also tried looking in Google Cloud Monitoring, but couldn't find any means of figuring out what's the queue size in my topics.
Since I plan on using PubSub for analytics, it's important for me to monitor the queue count, so I could scale up/down the subscriber count.
What am I missing?
Multiple subscribers can make pull calls to the same "shared" subscription. Each subscriber receives a subset of the messages. The push endpoint can be a load balancer. The Pub/Sub service automatically balances the load.
Resource limits There is no limit on the number of retained messages.
The metric you want to look at is "undelivered messages." You should be able to set up alerts or charts that monitor this metric in Google Cloud Monitoring under the "Pub/Sub Subscription" resource type. The number of messages that have not yet been acknowledged by subscribers, i.e., queue size, is a per-subscription metric as opposed to a per-topic metric. For info on the metric, see pubsub.googleapis.com/subscription/num_undelivered_messages
in the GCP Metrics List (and others for all of the Pub/Sub metrics available).
This might help if you're looking into a programmatic way to achieve this:
from google.cloud import monitoring_v3
from google.cloud.monitoring_v3 import query
project = "my-project"
client = monitoring_v3.MetricServiceClient()
result = query.Query(
client,
project,
'pubsub.googleapis.com/subscription/num_undelivered_messages',
minutes=60).as_dataframe()
print(result['pubsub_subscription'][project]['subscription_name'][0])
The answer to your question is "no", there is no feature for PubSub that shows these counts. The way you have to do it is via log event monitoring using Stackdriver (it took me some time to find that out too).
The colloquial answer to this is do the following, step-by-step:
Monitoring
Dashboards
> Create Dashboard
Add Chart
button top-right of dashboard screennum_undelivered_messages
and then SAVE
Updated version based on @steeve's answer. (without pandas
dependency)
Please note that you have to specify end_time
instead of using default utcnow()
.
import datetime
from google.cloud import monitoring_v3
from google.cloud.monitoring_v3 import query
project = 'my-project'
sub_name = 'my-sub'
client = monitoring_v3.MetricServiceClient()
result = query.Query(
client,
project,
'pubsub.googleapis.com/subscription/num_undelivered_messages',
end_time=datetime.datetime.now(),
minutes=1,
).select_resources(subscription_id=sub_name)
for content in result:
print(content.points[0].value.int64_value)
Here is a java version
package com.example.monitoring;
import static com.google.cloud.monitoring.v3.MetricServiceClient.create;
import static com.google.monitoring.v3.ListTimeSeriesRequest.newBuilder;
import static com.google.monitoring.v3.ProjectName.of;
import static com.google.protobuf.util.Timestamps.fromMillis;
import static java.lang.System.currentTimeMillis;
import com.google.monitoring.v3.ListTimeSeriesRequest;
import com.google.monitoring.v3.TimeInterval;
public class ReadMessagesFromGcp {
public static void main(String... args) throws Exception {
String projectId = "put here";
var interval = TimeInterval.newBuilder()
.setStartTime(fromMillis(currentTimeMillis() - (120 * 1000)))
.setEndTime(fromMillis(currentTimeMillis()))
.build();
var request = newBuilder().setName(of(projectId).toString())
.setFilter("metric.type=\"pubsub.googleapis.com/subscription/num_undelivered_messages\"")
.setInterval(interval)
.setView(ListTimeSeriesRequest.TimeSeriesView.FULL)
.build();
var response = create().listTimeSeries(request);
for (var subscriptionData : response.iterateAll()) {
var subscription = subscriptionData.getResource().getLabelsMap().get("subscription_id");
var numberOrMessages = subscriptionData.getPointsList().get(0).getValue().getInt64Value();
if(numberOrMessages > 0) {
System.out.println(subscription + " has " + numberOrMessages + " messages ");
}
}
}
}
<dependency>
<groupId>com.google.cloud</groupId>
<artifactId>google-cloud-monitoring</artifactId>
<version>3.3.2</version>
</dependency>
<dependency>
<groupId>com.google.protobuf</groupId>
<artifactId>protobuf-java-util</artifactId>
<version>4.0.0-rc-2</version>
</dependency>
output
queue-1 has 36 messages
queue-2 has 4 messages
queue-3 has 3 messages
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