| Commit message (Collapse) | Author | Age | Files | Lines |
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This basically reverts 8da30ad6be34339124ba4cb4e36aea260dda12bc
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The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.
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`each_with_object` allocates an array for each kv pair. Switching to
the slightly more verbose but less allocatey `each_pair` eliminates
array allocations. Eliminating this allocation returns AR objects to
have constant array allocations regardless of the number of columns the
object has.
Here is test code:
```ruby
require 'active_record'
class Topic < ActiveRecord::Base
end
20.times do |i|
Process.waitpid fork {
ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'
ActiveRecord::Base.connection.instance_eval do
create_table(:topics) do |t|
t.string :title, limit: 250
t.string :author_name
t.string :author_email_address
t.string :parent_title
t.string :type
t.string :group
i.times do |j|
t.string :"aaa#{j}"
end
t.timestamps null: true
end
end
ObjectSpace::AllocationTracer.setup(%i{type})
Topic.create title: "aaron" # heat cache
result = ObjectSpace::AllocationTracer.trace do
10.times do |i|
Topic.create title: "aaron #{i}"
end
end
puts "#{Topic.columns.length},#{(result.find { |k,v| k.first == :T_ARRAY }.last.first / 10)}"
}
end
```
Before this commit:
```
9,166
10,167
11,168
12,169
13,170
14,171
15,172
16,173
17,174
18,175
19,176
20,177
21,178
22,179
23,180
24,181
25,182
26,183
27,184
28,185
```
After:
```
9,157
10,157
11,157
12,157
13,157
14,157
15,157
16,157
17,157
18,157
19,157
20,157
21,157
22,157
23,157
24,157
25,157
26,157
27,157
28,157
```
Left side is the number of columns, right is the number of allocations
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deep_dup'ing a hash will dup the keys as well as the values. Since
string keys from the source hash will be frozen, and the dup'd objects
are immediately dup'd and frozen on insert in to the hash, the end user
will only ever see two frozen strings. Since the strings are immutable,
this commit just cheats a little and reuses the immutable strings.
Just to reiterate, before this commit, deep duping a hash that looks
like this: `{ "foo" => "bar" }` will generate two new instances of
"foo". One is created when `deep_dup` is called on "foo", and the other
is created when the newly allocated "foo" string is inserted in to the
hash. The user never sees the intermediate "foo", and both copies of
"foo" that the user *can* access will be frozen, so in this case we just
reuse the existing frozen key.
The upshot is that after this change, string allocations on AR
allocations become constant regardless of the number of columns the
model has.
```ruby
require 'active_record'
class Topic < ActiveRecord::Base
end
20.times do |i|
Process.waitpid fork {
ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'
ActiveRecord::Base.connection.instance_eval do
create_table(:topics) do |t|
t.string :title, limit: 250
t.string :author_name
t.string :author_email_address
t.string :parent_title
t.string :type
t.string :group
i.times do |j|
t.integer :"aaa#{j}"
end
t.timestamps null: true
end
end
ObjectSpace::AllocationTracer.setup(%i{type})
Topic.create title: "aaron" # heat cache
result = ObjectSpace::AllocationTracer.trace do
10.times do |i|
Topic.create title: "aaron #{i}"
end
end
puts "#{Topic.columns.length},#{(result.find { |k,v| k.first == :T_STRING }.last.first / 10)}"
}
end
```
If you run the above script before this commit, the output looks like
this:
```
[aaron@TC rails (master)]$ be ruby -rallocation_tracer test.rb
9,105
10,107
11,109
12,111
13,113
14,115
15,117
16,119
17,121
18,123
19,125
20,127
21,129
22,131
23,133
24,135
25,137
26,139
27,141
28,143
```
The left column is the number of methods, the right column is the number
of string allocations.
Running against this commit, the output is:
```
[aaron@TC rails (master)]$ be ruby -rallocation_tracer test.rb
9,87
10,87
11,87
12,87
13,87
14,87
15,87
16,87
17,87
18,87
19,87
20,87
21,87
22,87
23,87
24,87
25,87
26,87
27,87
28,87
```
As you can see, there is now only a constant number of strings
allocated, regardless of the number of columns the model has.
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According to our guideline, we leave 1 space between `#` and `=>`, so we
want `# =>` instead of `#=>`.
Thanks to @fxn for the suggestion.
[ci skip]
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Sometimes, on Mac OS X, programmers accidentally press Option+Space
rather than just Space and don’t see the difference. The problem is
that Option+Space writes a non-breaking space (0XA0) rather than a
normal space (0x20).
This commit removes all the non-breaking spaces inadvertently
introduced in the comments of the code.
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