[Feature Request]: Secondary index for string column type should be order preserved

[yingfeng]

Is there an existing issue for the same feature request?

• I have checked the existing issues.

Is your feature request related to a problem?

No response

Describe the feature you'd like

Currently, secondary index is built over PGM index which can only accept numeric values. For string types, they are hashed into PGM index, and therefore the range filter does not work for string column filters.

Describe implementation you've considered

No response

Documentation, adoption, use case

No response

Additional information

No response

[wuxiaobai24]

The PGM index doesn’t seem very suitable for string types, so we might need to introduce other index structures. Do you have any preference?

[yingfeng]

Currently, the secondary index has two types: HighCardinality and LowCardinality, PGM is used for the former and roaring bitmap based one is used for the latter one. Also, range filter can be performed on the string column data.