Hello,

I’m observing very strange and large memory allocations while solving a standard ODE and evaluating it at given times. However, after the first benchmark, if (and only if!) I recompile the integrated function these allocations disappear.

```
using BenchmarkTools
import DifferentialEquations: Vern9, ODEProblem, solve
```

The function I’m integrating is:

```
@inbounds function dyn_twobody!(du::Vector{Float64}, u::Vector{Float64},
GM::Float64, t::Float64)
r = (u[1]*u[1] + u[2]*u[2] + u[3]*u[3])^1.5
du[1] = u[4]
du[2] = u[5]
du[3] = u[6]
du[4] = -GM*u[1]/r
du[5] = -GM*u[2]/r
du[6] = -GM*u[3]/r
nothing
end
```

while `test`

is the function that evaluates the solution at the given times:

```
function test(x::Vector{Float64}, tms::Vector{Float64})
GM_MOON = 4.902780137400001e3;
user_prob = ODEProblem(dyn_twobody!, x, [0., 86400], GM_MOON)
user_sol = solve(user_prob, Vern9(), abstol=1e-10, reltol=1e-9, saveat=tms, save_everystep=false).u
return user_sol
end
```

Calling it with:

```
x = [50500., 232., 32321., -1.2, 0.01, 0.3];
tms = collect(LinRange(0., 86400., 86400));
@benchmark test($x, $tms)
```

yields:

```
BenchmarkTools.Trial: 30 samples with 1 evaluation.
Range (min … max): 129.553 ms … 535.830 ms ┊ GC (min … max): 11.32% … 74.42%
Time (median): 151.338 ms ┊ GC (median): 14.82%
Time (mean ± σ): 167.691 ms ± 71.469 ms ┊ GC (mean ± σ): 21.46% ± 11.46%
██
▆▇██▆▁▆▁▆▄▄▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▄ ▁
130 ms Histogram: frequency by time 536 ms <
Memory estimate: 304.61 MiB, allocs estimate: 432505.
```

If i recompile `dyn_twobody!`

the new benchmark is:

```
BenchmarkTools.Trial: 81 samples with 1 evaluation.
Range (min … max): 49.294 ms … 106.972 ms ┊ GC (min … max): 0.00% … 0.00%
Time (median): 59.441 ms ┊ GC (median): 0.00%
Time (mean ± σ): 62.334 ms ± 12.016 ms ┊ GC (mean ± σ): 2.41% ± 4.19%
█ ▁ ▁▁ ▃
█▆█▇▄▇▇██▇▆▇▇█▁▇▆▆▆▆▄▆▆▆▄▄▁▁▄▁▁▆▆▁▁▁▄▁▁▁▁▁▁▁▆▁▁▄▁▄▄▁▁▁▁▁▁▁▁▄ ▁
49.3 ms Histogram: frequency by time 98.8 ms <
Memory estimate: 17.22 MiB, allocs estimate: 173311.
```

Any idea what’s happening with my code? I see the Garbage Collector is taking quite a lot of time