[improve][io] Remove sleep when sourceTask.poll of kafka return null

[shibd]

Motivation

We observe our debezium source connector latency min is 1s when traffic is small.

According to the Kafka Source API definition, when there is no data, the implementation should block for a period of time. We don't need to actively sleep here to avoid CPU spinning.

"platform/resource/debezium-postgres-source-0" #20 prio=5 os_prio=0 cpu=15396.95ms elapsed=21030.80s tid=0x00007f8cbc99f020 nid=0x20 waiting on condition  [0x00007f8cbb92c000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
	at java.lang.Thread.sleep([email protected]/Native Method)
	at org.apache.pulsar.io.kafka.connect.AbstractKafkaConnectSource.read(AbstractKafkaConnectSource.java:172)
	- locked <0x00000000cf3044a0> (a org.apache.pulsar.io.debezium.postgres.DebeziumPostgresSource)
	at org.apache.pulsar.functions.instance.JavaInstanceRunnable.readInput(JavaInstanceRunnable.java:529)
	at org.apache.pulsar.functions.instance.JavaInstanceRunnable.run(JavaInstanceRunnable.java:320)
	at java.lang.Thread.run([email protected]/Thread.java:840)

Modifications

• Remove sleep when sourceTask.poll of kafka return null

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.27%. Comparing base (bbc6224) to head (5c9cf1a).
Report is 986 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #24124      +/-   ##
============================================
+ Coverage     73.57%   74.27%   +0.70%     
+ Complexity    32624    32114     -510     
============================================
  Files          1877     1864      -13     
  Lines        139502   144440    +4938     
  Branches      15299    16468    +1169     
============================================
+ Hits         102638   107285    +4647     
+ Misses        28908    28709     -199     
- Partials       7956     8446     +490     

Flag	Coverage Δ
inttests	26.77% <ø> (+2.18%)	⬆️
systests	23.13% <ø> (-1.19%)	⬇️
unittests	73.78% <ø> (+0.93%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...r/io/kafka/connect/AbstractKafkaConnectSource.java	63.28% <ø> (+1.68%)	⬆️

... and 1063 files with indirect coverage changes

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