[GitHub] [hudi] voonhous commented on pull request #8579: [MINOR] Added docs for gotchas when using PartialUpdateAvroPayload

["voonhous (via GitHub)" <gi...@apache.org>]

voonhous commented on PR #8579:
URL: https://github.com/apache/hudi/pull/8579#issuecomment-1523138078

   > > Results will be different if combineAndUpdateValue is invoked in order without invoking preCombine.
   > 
   > What is exactly lost here?
   
   
   # PreCombine + combineAndGetUpdateValue
   
   ```
   Table schema: {id: int , name: string, price: double, _ts: int}
   recordKey: id
   precombineField: _ts
   
   Table initial state:
   [1    a1_0    10.0    1001]
   
   Table performs an update with an incoming batch that has the following results (2):
   (precombine + combineAndGetUpdateValue)
   [
     [1    a1_0    11.0     999],
     [1    a1_0    null     1001]
   ]
   
   End state of the table:
   [1    a1_0    11.0    1001]
   
   ```
   
   This is so as the incoming batch at (2) will be `preCombine` before performing a `combineAndUpdateValue`.
   
   # combineAndGetUpdateValue ONLY
   
   Results will be different if `combineAndUpdateValue` is invoked in order without invoking `preCombine`.
   
   Example:
   ```
   Table initial state:
   [1    a1_0    10.0    1001]
   
   Table performs an update: 
   (combineAndGetUpdateValue)
   [1    a1_0    11.0     999]
   
   Table performs an update again: 
   (combineAndGetUpdateValue)
   [1    a1_0   null     1001]
   
   End state of the table:
   [1    a1_0   10.0    1001]
   ```
   
   [
     [1    a1_0    11.0     999],
     [1    a1_0    null     1001]
   ]
   
   End state of the table:
   [1    a1_0    11.0    1001]


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