xinyiZzz opened a new pull request, #19338:
URL: https://github.com/apache/doris/pull/19338

   # Proposed changes
   
   Issue Number: close #xxx
   
   ## Problem summary
   
   session variable `scanner_once_block_num` support the maximum number of 
blocks returned by each scanning. Instead of maximum number of data rows 
returned by each scanning thread in a single execution.
   
   In some scenarios, modify `scanner_once_block_num` which will be faster and 
use less memory.
   
   The default `scanner_once_block_num=5`, which is the same behavior as the 
previous `doris_scanner_row_num=16384`.
   
   For large and wide table queries with 800 columns, adjust 
`scanner_once_block_num=1`, 
   the time-cost is from 0.6s -> 0.4s, 
   and the memory is only used by 40% of the previous one.
   ```
   select * from tbl where str1="" and str2="" and str3=""
   ```
   
   ## Checklist(Required)
   
   * [ ] Does it affect the original behavior
   * [ ] Has unit tests been added
   * [ ] Has document been added or modified
   * [ ] Does it need to update dependencies
   * [ ] Is this PR support rollback (If NO, please explain WHY)
   
   ## Further comments
   
   If this is a relatively large or complex change, kick off the discussion at 
[d...@doris.apache.org](mailto:d...@doris.apache.org) by explaining why you 
chose the solution you did and what alternatives you considered, etc...
   
   


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