Support for OrderBy(..) in Async LINQ queries

[KrzysFR]

Currently, the Async LINQ queries to do not support the OrderBy(...) operator. You have to first call ToListAsync() and then sort the results in memory (using the regular LINQ-To-Object OrderBy(...).ToList().

The main issue with this operator, is that it must first buffer all the results in memory, before being able to sort them (the last one would be the first result once sorted). And then when the sorting is done, it will output all the results in burst. In effect, the first call to MoveNext() will take a very long time (99% of the query time), and then all successive MoveNext() calls will be instant and non-async (they will simply return the next item in an array).

As long as people use this as the last step in a query, with low item count, or with very selective Where(...) clauses in front, this should be OK.

Anyway, there does not seem to be any magical solution around this problem, and I hope that users of the API will think about what they do before doing something like tr.GetRange(subspaceWith10MillionKeys.ToRange()).OrderBy(kvp => ...).Take(10).ToListAsync() (which would need to read all 10 million keys, sort them all in memory, and then only take the first 10.

[KrzysFR]

First part of the work done in 713b793

[mohammadmaheer]

What about if I do have a list of objects and I want to use OrderBy(x=>x.SomeProperty)?
Here, I don't have benefit of async. Any thoughts?