andygrove commented on issue #1098:
URL: 
https://github.com/apache/datafusion-comet/issues/1098#issuecomment-2486453783

   This is getting pretty interesting. I improved the native explain feature in 
https://github.com/apache/datafusion-comet/pull/1099 and we now see the 
planning time. The following trivial plan takes more than a second to plan.
   
   ```
   24/11/19 11:25:26 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.304405241s):
    ShuffleWriterExec: partitioning=UnknownPartitioning(1)
     ScanExec: source=[], schema=[col_0: Int64, col_1: Decimal128(34, 4), 
col_2: Date32, col_3: Int32]
   ```
   
   I also added a criterion benchmark to plan this query in the same PR, and it 
only takes 23 *microseconds*.
   
   Another observation is that the planning time increases each time:
   
   ```
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.377855944s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.403194796s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.424167789s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.487451934s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.492228413s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.517392898s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.534502296s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.556645236s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.622664488s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.622664287s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.730488921s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.730601884s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.730662237s):
   24/11/19 11:25:24 INFO core/src/execution/jni_api.rs: Comet native query 
plan (planning took 1.73067477s):
   ```
   
   Something strange is happening here. Does this indicate that some sort of 
contention or locking is happening which is resulting in these long times?


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