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https://issues.apache.org/jira/browse/COUCHDB-1130?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Randall Leeds updated COUCHDB-1130:
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Attachment: prof_bin_opt
Here's a runnable escript that exercises the original version, the patched
version I uploaded before, and a third version that tries to avoid the match
context stuff I talked about.
Since the docs I linked are super confusing I'm not going to try to dig too far
into explanations by my findings are:
The original version is slowest.
The first patch is faster.
The third version (in the escript) is even faster.
We're talking 1us or 2us per call.
If there's a difference in memory consumption I can't tell from any of the
output or any of the erlang:system_info or erlang:memory functions. But then, I
didn't try to mess with the tracers or profiles to see what memory consumption
is like mid-execution, so maybe all the resources used are already freed at the
end of the test.
Anyway. Do with this what you will. It's a small perf gain but if it's
reproducible it's a pretty critical code path to optimize so I say go for it?
I also tried flipping the order of the tests around just in case that had any
affect, but the results are consistent.
> binary optimization in couch_file
> ---------------------------------
>
> Key: COUCHDB-1130
> URL: https://issues.apache.org/jira/browse/COUCHDB-1130
> Project: CouchDB
> Issue Type: Improvement
> Components: Database Core
> Affects Versions: 1.0.2
> Reporter: Randall Leeds
> Priority: Minor
> Attachments:
> 0001-refactor-remove_block_prefixes-2-for-optimization.patch, prof_bin_opt
>
>
> I've had this patch sitting around since January and kept forgetting to file
> the ticket. Hurray spring cleaning.
> Just for fun I ran erlc with +bin_opt_info, which gives information about how
> the Erlang VM can optimize creating binary objects.
> What follows is the commit message from my patch.
> Even if I'm wrong about the last point, it can't hurt.
> What think you all?
> -------------------
> Running erlc with +bin_opt_info gives an INFO message stating that "matching
> anything else but a plain variable to the left of a binary pattern will
> prevent
> delayed sub binary optimization; SUGGEST changing argument order"
> I guess matching 0 is triggering this. If I understand correctly, this change
> will allow the compiler to skip creating a sub-binary that starts at the block
> boundary in the third clause and delay creation until we strip the leading
> byte
> in the 0 clause. This means one less 1-byte binary every time we read across a
> block boundary.
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