[GitHub] [incubator-doris] chaoyli commented on issue #5142: Optimize nested type implementation

[GitBox <gi...@apache.org>]

chaoyli commented on issue #5142:
URL: https://github.com/apache/incubator-doris/issues/5142#issuecomment-750837917


   To better understand and reduce copy in memory for **array_contains, array_slice, flatten** function.
   It's better to distinguish the memory layout and disk layout.
   ```
   The memory layout:
    
   Two-level data : [[1, 2], [3, 4]], [[5, 6, 7], null, [8]], [[9, 10]]
   
   * First Level Offsets (int32), First Level have no nulls
   
     | Bytes 0-3  | Bytes 4-7  | Bytes 8-11 | Bytes 12-15 |
     |------------|------------|------------|-------------|
     | 0          |  2         |  5         |  6          |
   
     * Second Nulls (uint8)
   
       | Byte 1- 3 | Bytes 4  | Bytes 5 - 7|
       |-----------------------------------|
       | 0         | 1        | 0          |
   
     * Second Level Offsets (int32)
   
       | Bytes 0-27           |
       |----------------------|
       | 0, 2, 4, 7, 7, 8, 10 |
   
     * Elements array (int32):
   
       | Bytes 0-9                     |
       |-------------------------------|
       | 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 |
   ```
   Like the above, every level in array only stores nulls and offsets.
   And also, offsets will store zero to calculate the first size.
   
   


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