lhotari commented on issue #25046:
URL: https://github.com/apache/pulsar/issues/25046#issuecomment-3631976371

   > [@lhotari](https://github.com/lhotari) Thank you so much for your help! 
When I ran pressure tests with 1KB small messages, the performance was solid 
and stable—only partition imbalance occurred, with a TPS of around 250K. 
However, when consuming 500KB large messages, performance degrades after a few 
minutes, paired with severe partition consumption imbalance. The most critical 
issue is that the consumption rate metrics for partitions vanish entirely: 
neither pulsar-manager API queries nor the pulsar_rate_out metric returns any 
data (this affects all brokers). Other metrics appear normal, and no thread 
blockages were detected in the broker thread dumps. Additionally, no priority 
distinctions were configured for the consumers.
   
   Have you configured `managedLedgerMaxReadsInFlightSizeInMB` to a reasonable 
value? The feature isn't enabled by default. It was added in 2.11 with #18245 
and improved later in #23901 . There's some details about broker memory limits 
in PIP-442 
https://github.com/apache/pulsar/blob/master/pip/pip-442.md#existing-broker-memory-management
  .  
   If you haven't configured `managedLedgerMaxReadsInFlightSizeInMB`, the 
broker can get overloaded with a large amount of consumers. You can try setting 
it to a value like 500 MB when you have at least 4GB of direct memory 
available. 


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