[FOLLOWUP] feat(docs): Add documents for the two bufferSize configs.

[lwllvyb]

What changes were proposed in this pull request?

Add documents for the two bufferSize configs in server_guide.md.

Why are the changes needed?

Fix: #2209

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Tested locally.

[jerqi]

Maybe this could be used for HDFS, too.

[lwllvyb]

Maybe this could be used for HDFS, too.

Thanks for your suggestion. I will update this PR.
and I will add a new PR to handle with the HDFS. #2216

[github-actions]

Test Results

 2 926 files  +22   2 926 suites  +22   6h 16m 24s ⏱️ + 15m 13s
 1 049 tests ± 0   1 047 ✅ + 1   2 💤 ±0  0 ❌  - 1 
13 045 runs  +51  13 015 ✅ +52  30 💤 ±0  0 ❌  - 1 

Results for commit 2c34ed7. ± Comparison against base commit 3a35b0f.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.28%. Comparing base (9f8951f) to head (8b39960).
Report is 7 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2213      +/-   ##
============================================
+ Coverage     52.35%   53.28%   +0.93%     
- Complexity     2815     3213     +398     
============================================
  Files           452      480      +28     
  Lines         21217    26060    +4843     
  Branches       1950     2463     +513     
============================================
+ Hits          11108    13887    +2779     
- Misses         9401    11267    +1866     
- Partials        708      906     +198     

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