Default write strategy is a little unexpected

[gatesn]

• Why do we store sum in the zone map?
• min/max_is_truncated does not compress to constant if possible in zone map
• sum stat in zone map is not compressed (e.g. narrowed, or bitpacked)

[robert3005]

The is_truncated is there for fixed sized columns since we thought it would be simpler to have uniform handling and it’s a constant bool column

[robert3005]

FWIW the sum in zone map is for pushdown in DF. However, DF had a very bad performance when using sum stat. They have fixed the behaviour on develop apache/datafusion#20768 but it's not released yet