Feature #13884: Reduce number of memory allocations for "and", "or" and "diff" operations on small arrays

• Status: Closed
• Assignee: DmitryBochkarev (Dmitry Bochkarev)
• Target version: -

[DmitryBochkarev (Dmitry Bochkarev)]

Very often, arrays are used to filter parameters and to select interesting items from 2 collections and very often these collections are small enough, for example:

SAFE_COLUMNS = [:id, :title, :created_at]

def columns
  @all_columns & SAFE_COLUMNS
end

In this patch, I got rid of unnecessary memory allocations for small arrays when "and", "or" and "diff" operations are performed.

I tested this patch on 64 architecture and found out that in arrays with 32 elements, element search is performed faster than retrieving an element from the hash (tested on collections with 16, 32, 64 and 128 elements).

[Eregon (Benoit Daloze)]

Note that this would change the semantics as it uses #== and not #eql? to compare elements.
The comparison should always be done with #eql? to remain compatible.

It also does not call #hash but that is likely a much smaller problem.

[DmitryBochkarev (Dmitry Bochkarev)]

Eregon (Benoit Daloze) wrote:

Note that this would change the semantics as it uses #== and not #eql? to compare elements.
The comparison should always be done with #eql? to remain compatible.

Yes, it is, I've missed this part, will fix.

[DmitryBochkarev (Dmitry Bochkarev)]

• File bmlog-20170911-205052.26491.tsv bmlog-20170911-205052.26491.tsv added
• File bmlog-20170911-205459.26568.tsv bmlog-20170911-205459.26568.tsv added
• File array_opt2.diff array_opt2.diff added

The fixed remark about comparison method. Added benchmarks and results.

After this benchmark, i've noticed there are no profits when array size between 17 and 32 elements, but some degradation of speed for "diff" operation.

Results

SMALL_ARRAY_MIN=1 SMALL_ARRAY_MAX=8 SMALL_ARRAY_ITERATIONS=10000

name	HEAD	PATCH
array_small_and	0.615	0.263
array_small_diff	0.676	0.282
array_small_or	0.953	0.463

name	PATCH
array_small_and	2.343
array_small_diff	2.392
array_small_or	2.056

SMALL_ARRAY_MIN=9 SMALL_ARRAY_MAX=16 SMALL_ARRAY_ITERATIONS=10000

name	HEAD	PATCH
array_small_and	1.429	1.005
array_small_diff	1.493	0.878
array_small_or	1.672	1.152

name	PATCH
array_small_and	1.422
array_small_diff	1.700
array_small_or	1.452

[DmitryBochkarev (Dmitry Bochkarev)]

• Tracker changed from Misc to Feature

[DmitryBochkarev (Dmitry Bochkarev)]

Can anyone review this patch?

[DmitryBochkarev (Dmitry Bochkarev)]

Send request to Github https://github.com/ruby/ruby/pull/1709

[matz (Yukihiro Matsumoto)]

I like the idea. Nobu, could you review?

Matz.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset trunk|r60057.

---

array.c: improve operations on small arrays

[Feature #13884]

Reduce number of memory allocations for "and", "or" and "diff"
operations on small arrays

Very often, arrays are used to filter parameters and to select
interesting items from 2 collections and very often these
collections are small enough, for example:

SAFE_COLUMNS = [:id, :title, :created_at]

def columns
  @all_columns & SAFE_COLUMNS
end

In this patch, I got rid of unnecessary memory allocations for
small arrays when "and", "or" and "diff" operations are performed.

name | HEAD | PATCH
-----------------+------:+------:
array_small_and | 0.615 | 0.263
array_small_diff | 0.676 | 0.282
array_small_or | 0.953 | 0.463

name | PATCH
-----------------+------:
array_small_and | 2.343
array_small_diff | 2.392
array_small_or | 2.056

name | HEAD | PATCH
-----------------+------:+------:
array_small_and | 1.429 | 1.005
array_small_diff | 1.493 | 0.878
array_small_or | 1.672 | 1.152

name | PATCH
-----------------+------:
array_small_and | 1.422
array_small_diff | 1.700
array_small_or | 1.452

Author: Dmitry Bochkarev [e-mail]