FunData Twitter Shootout -- OCaml
This is the OCaml version of the http://github.com/alexy/fundata1, implementing the Karmic Social Capital (KSC) on Twitter Communication Graph. The fundata1 repository contains all the necessary documentation about the shootout and data itself. Here we'll provide some implementation notes specific to OCaml.
The main executable is
sc.opt, natively compiled.
I tried to learn
omake here, and it builds the executable, but that then fails to process command line arguments properly. I'm probably missing something.
You have to set
OCAMLRUNPARAM or it will take forever. Smaller values may work:
export OCAMLRUNPARAM='h=5G;s=1G' time ./sc.opt <dreps> <dments> <dcaps> [maxDays]
It reads the graph from and , which can be either
.mlb files. The latter ones are the results of
save_graph.opt, reading in the former and saving in OCaml's own binary format via
Marshal.to_cahnnel. The result is uncompressed.
If you want to create a smaller version of the original graphs, you can use the
save_graph program. It's invoked as follows:
./save_graph.opt <orig.json.hdb> <save> [N] [progress]
If N is given, it will limit the number of entries read from the original -- only those will be used to build the OCaml graph and dump that into
<save>.mlb. If progress is given, a dot will be printed after so many entries; the default is 10,000.
This is a translation of http://github.com/alexy/husky, a Haskell implementation of KSC, into OCaml. At first, husky was crashing under ghc 6.12.1 which had a GC bug. While Simon Marlow valiantly fought and quashed it, I translated husky to clams.
Some things stand out in OCaml, e.g.
-- floating-point operators are distinct from integer ones, and contain a dot:
+. *. /.
-- Equality is tested with
== -- but
== 0. fails for
safeDivide x y doesn't check for
y = 0., but rather goes ahead with the division and then checks whether the result is
Just a Little Bit Imperative
OCaml's standard map data structure is an imperative
Hashtbl. At creation time, it wants to know how much to allocate; we just go ahead and allocate it all for the number of users, i.e.
let orderN = 5000000 in Hashtbl.create orderN;
Hence instead of folds, some operations are
List.iter, and all those updating a
Hashtbl have type
unit and value
(). This can present a moment's pause when translating back for a purely functional map.
Mauricio Fernandez and Mattias Giaovannini developed http://eigenclass.org/R2/writings/finite-map-benchmarks. Some are functional, like
ternary, some are imperative, like
Fasthashtbl. The latter works best when there's no deletions, which is the case.