[ISSUE #8765] fix low performance of delay message when enable rocksdb consume queue

[yuz10]

Which Issue(s) This PR Fixes

Fixes #8765

Brief Description

How Did You Test This Change?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 53.57143% with 13 lines in your changes missing coverage. Please review.

Project coverage is 47.35%. Comparing base (daf3d1a) to head (8bd91e3).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ache/rocketmq/store/queue/RocksDBConsumeQueue.java	53.57%	10 Missing and 3 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #8766      +/-   ##
=============================================
- Coverage      47.52%   47.35%   -0.17%     
+ Complexity     11592    11560      -32     
=============================================
  Files           1282     1282              
  Lines          89848    89882      +34     
  Branches       11557    11565       +8     
=============================================
- Hits           42697    42567     -130     
- Misses         41927    42056     +129     
- Partials        5224     5259      +35     

Flag	Coverage Δ
	47.35% <53.57%> (-0.17%)	⬇️

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[lizhanhui]

@yuz10 Is there profiling metrics verifying that prefetch actually improves perf?

[yuz10]

@yuz10 Is there profiling metrics verifying that prefetch actually improves perf?

The performance loss is not related to prefetching. The schedule message deliver speed is 160/s because every time the iterator only returns 16 messages, and the deliver thread will sleep 100ms after iterate finish. See org.apache.rocketmq.broker.schedule.ScheduleMessageService.DeliverDelayedMessageTimerTask#executeOnTimeUp

[yuz10]

@lizhanhui I found no difference between batch and single get key from rocksdb. I will remove prefetch code.
Batch:
QueryCQ iter 10489877 cost 20527
QueryCQ iter 10489877 cost 19496
QueryCQ iter 10489877 cost 19395

Single:
QueryCQ iter 10489877 cost 20313
QueryCQ iter 10489877 cost 19196
QueryCQ iter 10489877 cost 18945