Hmm..something feels off here - I did the following experiment on Arrow 11 and casting timestamp-naive to int64 is much faster than casting timestamp-naive to timestamp-utc:
In [16]: %time table.cast(schema_int) CPU times: user 114 µs, sys: 30 µs, total: 144 µs *Wall time: 231 µs* Out[16]: pyarrow.Table time: int64 ---- time: [[0,1,2,3,4,...,99999995,99999996,99999997,99999998,99999999]] In [17]: %time table.cast(schema_tz) CPU times: user 119 ms, sys: 140 ms, total: 260 ms *Wall time: 259 ms* Out[17]: pyarrow.Table time: timestamp[ns, tz=UTC] ---- time: [[1970-01-01 00:00:00.000000000,1970-01-01 00:00:00.000000001,1970-01-01 00:00:00.000000002,1970-01-01 00:00:00.000000003,1970-01-01 00:00:00.000000004,...,1970-01-01 00:00:00.099999995,1970-01-01 00:00:00.099999996,1970-01-01 00:00:00.099999997,1970-01-01 00:00:00.099999998,1970-01-01 00:00:00.099999999]] In [18]: table Out[18]: pyarrow.Table time: timestamp[ns] ---- time: [[1970-01-01 00:00:00.000000000,1970-01-01 00:00:00.000000001,1970-01-01 00:00:00.000000002,1970-01-01 00:00:00.000000003,1970-01-01 00:00:00.000000004,...,1970-01-01 00:00:00.099999995,1970-01-01 00:00:00.099999996,1970-01-01 00:00:00.099999997,1970-01-01 00:00:00.099999998,1970-01-01 00:00:00.099999999]] On Wed, Feb 15, 2023 at 2:52 PM Rok Mihevc <rok.mih...@gmail.com> wrote: > I'm not sure about (1) but I'm pretty sure for (2) doing a cast of tz-aware > timestamp to tz-naive should be a metadata-only change. > > On Wed, Feb 15, 2023 at 4:19 PM Li Jin <ice.xell...@gmail.com> wrote: > > > Asking (2) because IIUC this is a metadata operation that could be zero > > copy but I am not sure if this is actually the case. > > > > On Wed, Feb 15, 2023 at 10:17 AM Li Jin <ice.xell...@gmail.com> wrote: > > > > > Hello! > > > > > > I have some questions about type casting memory usage with pyarrow > Table. > > > Let's say I have a pyarrow Table with 100 columns. > > > > > > (1) if I want to cast n columns to a different type (e.g., float to > int). > > > What is the smallest memory overhead that I can do? (memory overhead > of 1 > > > column, n columns or 100 columns?) > > > > > > (2) if I want to cast n timestamp columns from tz-native to tz-UTC. > What > > > is the smallest memory overhead that I can do? (0, 1 column, n columns > or > > > 100 columns?) > > > > > > Thanks! > > > Li > > > > > >
