simonvandel opened a new pull request, #9020:
URL: https://github.com/apache/arrow-datafusion/pull/9020

   ## Which issue does this PR close?
   
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   Relates to https://github.com/apache/arrow-datafusion/issues/5637
   
   ## Rationale for this change
   
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    Why are you proposing this change? If this is already explained clearly in 
the issue then this section is not needed.
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   Planning time of Datafusion is slow.
   
   ## What changes are included in this PR?
   
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   Profiling shows that a large part of planning is spent in `DFSchema::merge`.
   Before this PR, merging was complexity `O(N * M)`, where `N` and `M` are 
number of fields in the two schemas.
   With this PR, merging is complexity `O(N + M)` using a HashSet as an index.
   
   Speeds up benchmarks in sql_planner.rs by 18-75%. However, physical planning 
benchmarks seem to regress by 1.8%. I wonder if that is an acceptable trade?
   
   <details>
   
   <summary>Benchmark results</summary>
   
   ```
   Gnuplot not found, using plotters backend
   Benchmarking logical_select_one_from_700: Warming up for 3.0000 s
   Warning: Unable to complete 100 samples in 5.0s. You may wish to increase 
target time to 6.8s, enable flat sampling, or reduce sample count to 60.
   logical_select_one_from_700
                           time:   [1.3324 ms 1.3359 ms 1.3396 ms]
                           change: [-54.725% -54.348% -53.914%] (p = 0.00 < 
0.05)
                           Performance has improved.
   Found 14 outliers among 100 measurements (14.00%)
     6 (6.00%) low mild
     3 (3.00%) high mild
     5 (5.00%) high severe
   
   physical_select_one_from_700
                           time:   [4.6236 ms 4.6485 ms 4.6795 ms]
                           change: [-75.159% -74.941% -74.735%] (p = 0.00 < 
0.05)
                           Performance has improved.
   Found 8 outliers among 100 measurements (8.00%)
     3 (3.00%) high mild
     5 (5.00%) high severe
   
   Benchmarking logical_trivial_join_low_numbered_columns: Warming up for 
3.0000 s
   Warning: Unable to complete 100 samples in 5.0s. You may wish to increase 
target time to 6.8s, enable flat sampling, or reduce sample count to 60.
   logical_trivial_join_low_numbered_columns
                           time:   [1.3504 ms 1.3546 ms 1.3592 ms]
                           change: [-22.854% -22.042% -21.199%] (p = 0.00 < 
0.05)
                           Performance has improved.
   Found 11 outliers among 100 measurements (11.00%)
     1 (1.00%) low mild
     4 (4.00%) high mild
     6 (6.00%) high severe
   
   Benchmarking logical_trivial_join_high_numbered_columns: Warming up for 
3.0000 s
   Warning: Unable to complete 100 samples in 5.0s. You may wish to increase 
target time to 7.1s, enable flat sampling, or reduce sample count to 50.
   logical_trivial_join_high_numbered_columns
                           time:   [1.3961 ms 1.4003 ms 1.4051 ms]
                           change: [-21.654% -21.238% -20.848%] (p = 0.00 < 
0.05)
                           Performance has improved.
   Found 12 outliers among 100 measurements (12.00%)
     2 (2.00%) low mild
     8 (8.00%) high mild
     2 (2.00%) high severe
   
   Benchmarking logical_aggregate_with_join: Warming up for 3.0000 s
   Warning: Unable to complete 100 samples in 5.0s. You may wish to increase 
target time to 9.3s, enable flat sampling, or reduce sample count to 50.
   logical_aggregate_with_join
                           time:   [1.8286 ms 1.8331 ms 1.8381 ms]
                           change: [-18.973% -18.543% -18.126%] (p = 0.00 < 
0.05)
                           Performance has improved.
   Found 8 outliers among 100 measurements (8.00%)
     1 (1.00%) low mild
     6 (6.00%) high mild
     1 (1.00%) high severe
   
   physical_plan_tpch      time:   [5.6537 ms 5.6803 ms 5.7095 ms]
                           change: [+1.1125% +1.7618% +2.3821%] (p = 0.00 < 
0.05)
                           Performance has regressed.
   Found 9 outliers among 100 measurements (9.00%)
     6 (6.00%) high mild
     3 (3.00%) high severe
   ```
   </details>
   
   
   ## Are these changes tested?
   
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   Should be in existing tests.
   
   ## Are there any user-facing changes?
   
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   Faster planning.
   
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change` label.
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