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Posted to commits@pinot.apache.org by "gortiz (via GitHub)" <gi...@apache.org> on 2023/12/20 12:46:21 UTC

[I] Allow to add derived columns that depends on new columns [pinot]

gortiz opened a new issue, #12186:
URL: https://github.com/apache/pinot/issues/12186

   Right now Pinot fails when a table is modified in such a way that two columns are added and one of them depend on the other.
   
   More specifically, assuming table T has columns A1, A2 and A3, it should be possible to add columns B and C such as:
   
   ```js
   //table config
   "ingestionConfig": {
         "transformConfigs": [
           {
             "columnName": "C",
             "transformFunction": "B + 1"
           }
      ]
   }
   ```
   
   But right now this fails with:
   ```
   Caused by: java.lang.RuntimeException: Failed to create derived column: C because argument: B does not exist in the segment
   ```
   
   This error is thrown in https://github.com/apache/pinot/blob/85b5779cff8d33412937ceb6d4dfc972b6c8bd97/pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/index/loader/defaultcolumn/BaseDefaultColumnHandler.java#L374 when at least one of the columns used in the transform function is not included in the columns already stored in the segment.
   
   This is not a blocker because the same change can be done by first adding column B, reload and then modify the table again to add column D and reload.
   
   It is important to note that at the same time we add this feature we should add checks to avoid cycle dependencies. Specifically, it should be forbidden to add columns `E1, E2, ..., En` when `E1` depends on `En` and `Ek` depends on `E(k-1)` for all k in [1, n]. 


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