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[Fixes #11512] improves cache size calculation in ActiveSupport::Cach…

…e::MemoryStore

Previously, the cache size of `ActiveSupport::Cache::MemoryStore` was calculated
as the sum of the size of its entries, ignoring the size of keys and any data
structure overhead. This could lead to the calculated cache size sometimes being
10-100x smaller than the memory used, e.g., in the case of small values.

The size of a key/entry pair is now calculated via `#cached_size`:

    def cached_size(key, entry)
      key.to_s.bytesize + entry.size + PER_ENTRY_OVERHEAD
    end

The value of `PER_ENTRY_OVERHEAD` is 240 bytes based on an [empirical
estimation](https://gist.github.com/ssimeonov/6047200) for 64-bit MRI on
1.9.3 and 2.0.

Fixes GH#11512 #11512

Conflicts:
	activesupport/CHANGELOG.md
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1 parent 2f73ad7 commit bddb73e9c06c800a3309b90c73d2ac410f300727 @ssimeonov ssimeonov committed with drogus Jul 21, 2013
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@@ -1,5 +1,18 @@
## unreleased ##
+* Improve `ActiveSupport::Cache::MemoryStore` cache size calculation.
+ The memory used by a key/entry pair is calculated via `#cached_size`:
+
+ def cached_size(key, entry)
+ key.to_s.bytesize + entry.size + PER_ENTRY_OVERHEAD
+ end
+
+ The value of `PER_ENTRY_OVERHEAD` is 240 bytes based on an [empirical
+ estimation](https://gist.github.com/ssimeonov/6047200) for 64-bit MRI on
+ 1.9.3 and 2.0. GH#11512
+
+ *Simeon Simeonov*
+
* Only raise `Module::DelegationError` if it's the source of the exception.
Fixes #10559
@@ -122,6 +122,14 @@ def synchronize(&block) # :nodoc:
end
protected
+
+ # See https://gist.github.com/ssimeonov/6047200
+ PER_ENTRY_OVERHEAD = 240
+
+ def cached_size(key, entry)
+ key.to_s.bytesize + entry.size + PER_ENTRY_OVERHEAD
+ end
+
def read_entry(key, options) # :nodoc:
entry = @data[key]
synchronize do
@@ -139,8 +147,11 @@ def write_entry(key, entry, options) # :nodoc:
synchronize do
old_entry = @data[key]
return false if @data.key?(key) && options[:unless_exist]
- @cache_size -= old_entry.size if old_entry
- @cache_size += entry.size
+ if old_entry
+ @cache_size -= (old_entry.size - entry.size)
+ else
+ @cache_size += cached_size(key, entry)
+ end
@key_access[key] = Time.now.to_f
@data[key] = entry
prune(@max_size * 0.75, @max_prune_time) if @cache_size > @max_size
@@ -152,7 +163,7 @@ def delete_entry(key, options) # :nodoc:
synchronize do
@key_access.delete(key)
entry = @data.delete(key)
- @cache_size -= entry.size if entry
+ @cache_size -= cached_size(key, entry) if entry
!!entry
end
end
@@ -693,8 +693,8 @@ def test_log_exception_when_cache_read_fails
class MemoryStoreTest < ActiveSupport::TestCase
def setup
- @record_size = ActiveSupport::Cache::Entry.new("aaaaaaaaaa").size
- @cache = ActiveSupport::Cache.lookup_store(:memory_store, :expires_in => 60, :size => @record_size * 10)
+ @record_size = ActiveSupport::Cache.lookup_store(:memory_store).send(:cached_size, 1, ActiveSupport::Cache::Entry.new("aaaaaaaaaa"))
+ @cache = ActiveSupport::Cache.lookup_store(:memory_store, :expires_in => 60, :size => @record_size * 10 + 1)
end
include CacheStoreBehavior
@@ -744,6 +744,30 @@ def test_prune_size_on_write
assert !@cache.exist?(1), "no entry"
end
+ def test_prune_size_on_write_based_on_key_length
+ @cache.write(1, "aaaaaaaaaa") && sleep(0.001)
+ @cache.write(2, "bbbbbbbbbb") && sleep(0.001)
+ @cache.write(3, "cccccccccc") && sleep(0.001)
+ @cache.write(4, "dddddddddd") && sleep(0.001)
+ @cache.write(5, "eeeeeeeeee") && sleep(0.001)
+ @cache.write(6, "ffffffffff") && sleep(0.001)
+ @cache.write(7, "gggggggggg") && sleep(0.001)
+ @cache.write(8, "hhhhhhhhhh") && sleep(0.001)
+ @cache.write(9, "iiiiiiiiii") && sleep(0.001)
+ long_key = '*' * 2 * @record_size
+ @cache.write(long_key, "llllllllll")
+ assert @cache.exist?(long_key)
+ assert @cache.exist?(9)
+ assert @cache.exist?(8)
+ assert @cache.exist?(7)
+ assert @cache.exist?(6)
+ assert !@cache.exist?(5), "no entry"
+ assert !@cache.exist?(4), "no entry"
+ assert !@cache.exist?(3), "no entry"
+ assert !@cache.exist?(2), "no entry"
+ assert !@cache.exist?(1), "no entry"
+ end
+
def test_pruning_is_capped_at_a_max_time
def @cache.delete_entry (*args)
sleep(0.01)

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