dao-jun opened a new issue, #19601:
URL: https://github.com/apache/pulsar/issues/19601
### Motivation
Pulsar has 2 configurations for the backlog eviction:
`backlogQuotaDefaultLimitBytes` and `backlogQuotaDefaultLimitSecond`, if topic
backlog reaches the threshold of any item, backlog eviction will be triggered.
Before backlog eviction happens, we don't have a metric to monitor how long
that it can reaches the threshold.
We can provide a progress bar metric to tell users some topics is about to
trigger backlog eviction. And users can subscribe the alter to schedule
consumers.
### Goal
Provide a metric named `pulsar_backlog_eviction_proximity` in topic level.
### API Changes
_No response_
### Implementation
Because of there are 2 configurations for the backlog eviction, if topic
backlog reaches anyone of them will trigger the backlog eviction, so we need to
calculate both of them and select the max value:
```
long backlogQuotaLimitInBytes =
getBacklogQuota(BacklogQuotaType.destination_storage).getLimitSize();
int backlogQuotaLimitInSecond =
getBacklogQuota(BacklogQuotaType.message_age).getLimitTime();
long topicBacklogSize = getBacklogSize();
topicBacklogSize = topicBacklogSize < 0 ? 0 : topicBacklogSize;
long topicBacklogSeconds = getBacklogSeconds();
topicBacklogSeconds = topicBacklogSeconds < 0 ? 0 :
topicBacklogSeconds;
return Math.max(topicBacklogSize / backlogQuotaLimitInBytesD,
topicBacklogSeconds / backlogQuotaLimitInSecondD);
```
#### Metric
| Name | Type | Description | Labels |
| -- | -- | -- | -- |
| pulsar_backlog_eviction_proximity | Gauge | Proximity to trigger backlog
eviction. | cluster, tenant, namespace, topic, slowest_subscription |
### Alternatives
_No response_
### Anything else?
_No response_
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