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improve naive datetime decoding #320

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improve naive datetime decoding #320

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improve naive datetime decoding
ruslandoga Apr 20, 2026
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changelog
ruslandoga Apr 20, 2026
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ruslandoga Apr 20, 2026
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18 changes: 18 additions & 0 deletions bench/naive_decode.exs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
defmodule Bench do
@epoch_gregorian_seconds 62_167_219_200

def via_unix(seconds) do
seconds
|> DateTime.from_unix!()
|> DateTime.to_naive()
end

def via_gregorian(seconds) do
NaiveDateTime.from_gregorian_seconds(seconds + @epoch_gregorian_seconds)
end
end

Benchee.run(%{
"via_unix" => fn -> Enum.each(1..1_000_000, &Bench.via_unix/1) end,
"via_gregorian" => fn -> Enum.each(1..1_000_000, &Bench.via_gregorian/1) end
})

@ruslandoga ruslandoga Apr 20, 2026

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Operating System: macOS
CPU Information: Apple M2
Number of Available Cores: 8
Available memory: 8 GB
Elixir 1.19.5
Erlang 28.3
JIT enabled: true

Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
memory time: 0 ns
reduction time: 0 ns
parallel: 1
inputs: none specified
Estimated total run time: 14 s
Excluding outliers: false

Benchmarking via_gregorian ...
Benchmarking via_unix ...
Calculating statistics...
Formatting results...

Name                    ips        average  deviation         median         99th %
via_gregorian         22.29       44.86 ms     ±4.34%       44.25 ms       49.10 ms
via_unix               8.87      112.78 ms     ±1.92%      112.30 ms      116.65 ms

Comparison: 
via_gregorian         22.29
via_unix               8.87 - 2.51x slower +67.92 ms

8 changes: 3 additions & 5 deletions lib/ch/row_binary.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -1452,13 +1452,11 @@ defmodule Ch.RowBinary do
{:datetime, timezone} ->
case bin do
<<s::32-little, bin::bytes>> ->
dt = DateTime.from_unix!(s)

dt =
case timezone do
nil -> DateTime.to_naive(dt)
"UTC" -> dt
_ -> DateTime.shift_zone!(dt, timezone)
nil -> NaiveDateTime.from_gregorian_seconds(s + @epoch_gregorian_seconds)
"UTC" -> DateTime.from_unix!(s)
_ -> s |> DateTime.from_unix!() |> DateTime.shift_zone!(timezone)
end

decode_rows(types_rest, bin, [dt | row], rows, types)
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