[Python-Dev] A new dictionary implementation

[Michael Foord]

On 08/02/2012 15:16, Mark Shannon wrote:
> Hi,
>
> Version 2 is now available.
>
> Version 2 makes as few changes to tunable constants as possible, and 
> generally does not change iteration order (so repr() is unchanged).
> All tests pass (the only changes to tests are for sys.getsizeof() ).
>
> Repository: https://bitbucket.org/markshannon/cpython_new_dict
> Issue http://bugs.python.org/issue13903
>
> Performance changes are basically zero for non-OO code.
> Average -0.5% speed change on 2n3 benchamrks, a few benchmarks show
> a small reduction in memory use. (see notes below)
>
> GCbench uses 47% less memory and is 12% faster.
> 2to3, which seems to be the only "realistic" benchmark that runs on Py3,
> shows no change in speed and uses 10% less memory.

In your first version 2to3 used 28% less memory. Do you know why it's 
worse in this version?

Michael

>
> All benchmarks and tests performed on old, slow 32bit machine
> with linux.
> Do please try it on your machine(s).
>
> If accepted, the new dict implementation will allow a useful 
> optimisation of the LOAD_GLOBAL (and possibly LOAD_ATTR) bytecode:
> By testing to see if the (immutable) keys-tables is the expected table,
> the value can accessed directly by index, rather than by name.
>
> Cheers,
> Mark.
>
>
> Notes:
> All benchmarks from http://hg.python.org/benchmarks/
> using the -m flag to get memory usage data.
>
> I've ignored the json benchmarks which shows unstable behaviour
> on my machine.
> Tiny changes to the dict being serialized or to the random seed can 
> change the relative speed of my implementation vs CPython from -25% to 
> +10%.
> _______________________________________________
> Python-Dev mailing list
> Python-Dev at python.org
> http://mail.python.org/mailman/listinfo/python-dev
> Unsubscribe: 
> http://mail.python.org/mailman/options/python-dev/fuzzyman%40voidspace.org.uk
>


-- 
http://www.voidspace.org.uk/

May you do good and not evil
May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
-- the sqlite blessing http://www.sqlite.org/different.html