sollhui opened a new pull request, #66894:
URL: https://github.com/apache/doris/pull/66894

   ### What problem does this PR solve?
   
   Issue Number: None
   
   Related PR: #62007
   
   #### Problem summary
   
   When row binlog is enabled, a `GROUP` request flushes both the data memtable 
and the row-binlog memtable. These are two independent physical flush tasks, 
and both increment `flush_running_count`.
   
   Write backpressure previously compared this physical task count with the 
same configured limit used by a normal data-only memtable. As a result, 
row-binlog imports effectively had half of the configured logical flush 
concurrency. With a limit of 2, one group memtable could consume the entire 
allowance and subsequent writes had to wait, making memtable writing and 
flushing nearly serial.
   
   #### Changes
   
   - Keep the existing `flush_running_count` backpressure mechanism for 
storage-compute integrated mode.
   - Use `memtable_flush_running_count_limit * 2` for `GROUP` requests because 
each logical row-binlog memtable creates two physical flush tasks.
   - Keep the configured limit unchanged for normal data-only requests.
   
   #### Impact
   
   Row-binlog imports can use the intended logical memtable flush concurrency 
and keep memtable writing overlapped with flushing. Imports without row binlog 
are unchanged.
   
   ### Release note
   
   None
   
   ### Check List (For Author)
   
   - Test: Not run (per request)
   - Behavior changed: Yes. Row-binlog `GROUP` requests use an effective 
physical flush-task limit of twice the configured logical limit.
   - Does this need documentation: No
   


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