NanoDate significantly (us vs. ns) slower than DateTime

[liuyxpp]

It can be 50x slower. See the following benchmark:

julia> using Dates, NanoDates
julia> using BenchmarkTools: @btime
julia> tstr = "2024-09-23T19:32:06.202111"
julia> @btime NanoDate($tstr)
  3.261 μs (45 allocations: 1.93 KiB)
2024-09-23T19:32:06.202111
julia> tstr23 = tstr[1:23]
julia> @btime DateTime.($tstr23, dateformat"yyyy-mm-ddTHH:MM:SS.sss")
  61.379 ns (0 allocations: 0 bytes)
2024-09-23T19:32:06.202

Anyway to improve it?
It becomes significant when you have a column which millions timestamp string to be converted.

[JeffreySarnoff]

For the specific date format you show "2024-09-23T19:32:06.202111", you can use this:

using Dates, NanoDates

function MicroDate(str)
  n = length(str)
  n !== 26 && throw(ErrorException("bad NanoDate string (length ($n) != 26)"))
  dt = DateTime(str[1:23])
  NanoDate(dt, parse(Int, str[24:26])*1000)
end

using Dates, NanoDates, BenchmarkTools

function MicroDate(str)
  n = length(str)
  n !== 26 && throw(ErrorException("bad NanoDate string (length ($n) != 26)"))
  dt = DateTime(str[1:23])
  NanoDate(dt, parse(Int, str[24:26])*1000)
end

microsecs = "2024-09-23T19:32:06.202111"
millisecs = "2024-09-23T19:32:06.202"

# compare

julia> @btime DateTime(millisecs)
  71.914 ns (1 allocation: 16 bytes)
2024-09-23T19:32:06.202

julia> @btime MicroDate(microsecs)
  79.115 ns (3 allocations: 96 bytes)
2024-09-23T19:32:06.202111

To handle 0..9 subsecond digits more quickly is possible. Doing so for strings with time zone offsets is open for a PR submission.

[JeffreySarnoff]

Thank you for noticing this -- I will enfold the faster approach into the main code with the next release.

[liuyxpp]

Thank you! I currently using a workaround just as you do in MicroDate. :)