Yes, sendAsync should be the most frequently used async API and it's a critical path. I don't have a chance to check all other async methods, but I have checked receiveAsync as well. Unlike sendAsync, receiveAsync switches to a different thread pool (PulsarClientImpl#internalExecutorProvider) from #10352, so it does not have the similar issue, but it could still affect other processing. Here are my notes when I read the code.

Currently a PulsarClient will create the following thread pools:

internalExecutorProvider is used for:

• Execute message listener, callbacks of receiveAsync() and batchReceiveAsync() for consumers
• Many callbacks in TransactionMetaStoreHandler

externalExecutorProvider is used for:

• Trigger message listener
• Trigger consumer event listener

As you can see, transaction metadata processing could be affected. But I think it's because executors are used without any careful consideration. Before adding documents, we might need to think if the existing behavior should be documented.

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.26%. Comparing base (d272825) to head (02deefc).
⚠️ Report is 12 commits behind head on master.

@@             Coverage Diff              @@
##             master   #24601      +/-   ##
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+ Coverage     74.21%   74.26%   +0.04%     
+ Complexity    33142    33132      -10     
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  Files          1881     1881              
  Lines        146770   146776       +6     
  Branches      16859    16859              
============================================
+ Hits         108922   108998      +76     
+ Misses        29181    29112      -69     
+ Partials       8667     8666       -1