Refactor/remove unecessary inspect calls

[pmargreff]

Remove unnecessary inspect calls.

absinthe-graphql/absinthe#573 issue has shown a big percentual time to resolve queries after they're fetched from the database.

After some debug @jeroenvisser101 pointed one of the problems.

... I did some further investigation, and found that the inspect calls are actually made from dataloader: ce9ac3f#diff-cb130db1770f44aedd393088b4d91bcdR252 ...

It seems like some changes were made in the way errors are reported. Dataloader.Ecto seems to rely on errors to update pending batches, because it abuses fetch/3 to check if a value has previously been loaded. If we either added a argument to fetch/3 to toggle detailed errors, or to introduce fetched?/3 and used that in load/3, we would prevent inspect calls.

I got the call and refactored load creating a fetched?/3 function, so it will not pass through unnecessary inspect calls on both kv and ecto implementations.

Debugging the problem summed inspect calls represents 13% of the time (sample above).

'Elixir.Inspect.Atom':inspect/2                                                                   40000     0.18     5363  [      0.13]
'Elixir.Inspect.Algebra':'-container_doc/6-fun-0-'/4                                              50000     0.19     5622  [      0.11]
'Elixir.Inspect.Algebra':nest/2                                                                   10000     0.08     2290  [      0.23]
'Elixir.Inspect.Tuple':inspect/2                                                                  10000     0.05     1577  [      0.16]
'Elixir.Inspect.Map':inspect/3                                                                    10000     0.06     1715  [      0.17]
'Elixir.Inspect.PID':inspect/2                                                                    10000     0.06     1804  [      0.18]
'Elixir.Inspect.Algebra':container_each/6                                                         70000     0.42    12405  [      0.18]
'Elixir.Inspect.Algebra':flex_break/1                                                             50000     0.49    14245  [      0.28]
'Elixir.Inspect.Opts':'__struct__'/0                                                              10001     0.09     2494  [      0.25]
'Elixir.Inspect.Algebra':apply_nesting/3                                                          10000     0.09     2495  [      0.25]
'Elixir.Inspect.Algebra':group/2                                                                  20001     0.09     2775  [      0.14]
'Elixir.Inspect.Algebra':flex_glue/2                                                              50000     0.19     5665  [      0.11]
'Elixir.Inspect.Algebra':join/4                                                                   50000     0.22     6501  [      0.13]
'Elixir.Inspect.Algebra':flex_glue/3                                                              50000     0.22     6523  [      0.13]
'Elixir.Inspect.Atom':color_key/1                                                                 40000     0.32     9400  [      0.23]
'Elixir.Inspect':impl_for/1                                                                       70001     0.32     9406  [      0.13]
'Elixir.Inspect':'impl_for!'/1                                                                    70001     0.67    19677  [      0.28]
'Elixir.Inspect.Algebra':to_doc/2                                                                 70001     0.70    20405  [      0.29]
'Elixir.Inspect.Algebra':color/3                                                                 100001     0.81    23779  [      0.24]
'Elixir.Inspect.Algebra':decrement/1                                                              60000     1.08    31509  [      0.53]
'Elixir.Inspect.Algebra':concat/2                                                                180000     1.25    36417  [      0.20]
'Elixir.Inspect.Algebra':fold_doc/2                                                               60000     1.39    40727  [      0.68]
'Elixir.Inspect.Algebra':format/3                                                                410003     2.97    86865  [      0.21]

After the refactor the same query using Dataloader now goes from something like 11_502_307 to 8_260_419 fn calls. Complete results here.

[benwilson512]

Looks good in general, just some minor code tweaks.

[pmargreff]

@benwilson512 ping

[benwilson512]

Thank you!