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Allow to retry Couchbase::Bucket#cas on collitions
Extend Couchbase::Bucket#cas to take a `:retry` Fixnum option that specifies the maximum number of times the method should retry the entire get/update/set operation when a Couchbase::Error::KeyExists error is encountered due to a concurrent update from another writer between its #get and #set calls. Change-Id: Ibf7ebac9c63e460e05957004458e9e02ae803f89 Reviewed-on: http://review.couchbase.org/30336 Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com> Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
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Diff for: ‎lib/couchbase/bucket.rb

+31-4
Original file line numberDiff line numberDiff line change
@@ -35,12 +35,23 @@ class Bucket
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#
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# @see http://couchbase.com/docs/memcached-api/memcached-api-protocol-text_cas.html
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#
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# Setting the +:retry+ option to a positive number will cause this method
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# to rescue the {Couchbase::Error::KeyExists} error that happens when
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# an update collision is detected, and automatically get a fresh copy
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# of the value and retry the block. This will repeat as long as there
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# continues to be conflicts, up to the maximum number of retries specified.
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# For asynchronous mode, this means the block will be yielded once for
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# the initial {Bucket#get}, once for the final {Bucket#set} (successful
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# or last failure), and zero or more additional {Bucket#get} retries
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# in between, up to the maximum allowed by the +:retry+ option.
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#
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# @param [String, Symbol] key
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#
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# @param [Hash] options the options for "swap" part
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# @option options [Fixnum] :ttl (self.default_ttl) the time to live of this key
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# @option options [Symbol] :format (self.default_format) format of the value
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# @option options [Fixnum] :flags (self.default_flags) flags for this key
54+
# @option options [Fixnum] :retry (0) maximum number of times to autmatically retry upon update collision
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#
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# @yieldparam [Object, Result] value old value in synchronous mode and
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# +Result+ object in asynchronous mode.
@@ -80,16 +91,32 @@ class Bucket
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#
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# @return [Fixnum] the CAS of new value
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def cas(key, options = {})
94+
retries_remaining = options.delete(:retry) || 0
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if async?
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block = Proc.new
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get(key) do |ret|
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val = block.call(ret) # get new value from caller
87-
set(ret.key, val, options.merge(:cas => ret.cas, :flags => ret.flags), &block)
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set(ret.key, val, options.merge(:cas => ret.cas, :flags => ret.flags)) do |set_ret|
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if set_ret.error.is_a?(Couchbase::Error::KeyExists) && (retries_remaining > 0)
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cas(key, options.merge(:retry => retries_remaining - 1), &block)
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else
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block.call(set_ret)
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end
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end
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end
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else
90-
val, flags, ver = get(key, :extended => true)
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val = yield(val) # get new value from caller
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set(key, val, options.merge(:cas => ver, :flags => flags))
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begin
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val, flags, ver = get(key, :extended => true)
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val = yield(val) # get new value from caller
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set(key, val, options.merge(:cas => ver, :flags => flags))
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rescue Couchbase::Error::KeyExists
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if retries_remaining > 0
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retries_remaining -= 1
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retry
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else
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raise
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end
119+
end
93120
end
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end
95122
alias :compare_and_swap :cas

Diff for: ‎test/test_cas.rb

+111
Original file line numberDiff line numberDiff line change
@@ -57,6 +57,52 @@ def test_compare_and_swap_collision
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end
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end
5959

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def test_compare_and_swap_retry
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connection = Couchbase.new(:hostname => @mock.host, :port => @mock.port,
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:default_format => :document)
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connection.set(uniq_id, {"bar" => 1})
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calls = 0
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connection.cas(uniq_id, :retry => 1) do |val|
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calls += 1
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if calls == 1
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# Simulate collision with a separate writer. This will
69+
# change the CAS value to be different than what #cas just loaded.
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# Only do this the first time this block is executed.
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connection.set(uniq_id, {"bar" => 2})
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end
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# Complete the modification we desire, which should fail when set.
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val["baz"] = 3
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val
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end
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assert_equal 2, calls
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val = connection.get(uniq_id)
80+
expected = {"bar" => 2, "baz" => 3}
81+
assert_equal expected, val
82+
end
83+
84+
def test_compare_and_swap_too_many_retries
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connection = Couchbase.new(:hostname => @mock.host, :port => @mock.port,
86+
:default_format => :document)
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connection.set(uniq_id, {"bar" => 0})
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calls = 0
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assert_raises(Couchbase::Error::KeyExists) do
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connection.cas(uniq_id, :retry => 10) do |val|
91+
calls += 1
92+
93+
# Simulate collision with a separate writer. This will
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# change the CAS value to be different than what #cas just loaded.
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# Do it every time so we just keep retrying and failing.
96+
connection.set(uniq_id, {"bar" => calls})
97+
98+
# Complete the modification we desire, which should fail when set.
99+
val["baz"] = 3
100+
val
101+
end
102+
end
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assert_equal 11, calls
104+
end
105+
60106
def test_compare_and_swap_async
61107
connection = Couchbase.new(:hostname => @mock.host, :port => @mock.port,
62108
:default_format => :document)
@@ -113,6 +159,71 @@ def test_compare_and_swap_async_collision
113159
assert_equal 2, calls
114160
end
115161

162+
def test_compare_and_swap_async_retry
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connection = Couchbase.new(:hostname => @mock.host, :port => @mock.port,
164+
:default_format => :document)
165+
connection.set(uniq_id, {"bar" => 1})
166+
calls = 0
167+
connection.run do |conn|
168+
conn.cas(uniq_id, :retry => 1) do |ret|
169+
calls += 1
170+
case ret.operation
171+
when :get
172+
new_val = ret.value
173+
174+
if calls == 1
175+
# Simulate collision with a separate writer. This will
176+
# change the CAS value to be different than what #cas just loaded.
177+
# Only do this the first time this block is executed.
178+
connection.set(uniq_id, {"bar" => 2})
179+
end
180+
181+
# Complete the modification we desire, which should fail when set.
182+
new_val["baz"] = 3
183+
new_val
184+
when :set
185+
assert ret.success?
186+
else
187+
flunk "Unexpected operation: #{ret.operation.inspect}"
188+
end
189+
end
190+
end
191+
assert_equal 3, calls
192+
val = connection.get(uniq_id)
193+
expected = {"bar" => 2, "baz" => 3}
194+
assert_equal expected, val
195+
end
196+
197+
def test_compare_and_swap_async_too_many_retries
198+
connection = Couchbase.new(:hostname => @mock.host, :port => @mock.port,
199+
:default_format => :document)
200+
connection.set(uniq_id, {"bar" => 0})
201+
calls = 0
202+
connection.run do |conn|
203+
conn.cas(uniq_id, :retry => 10) do |ret|
204+
calls += 1
205+
case ret.operation
206+
when :get
207+
new_val = ret.value
208+
209+
# Simulate collision with a separate writer. This will
210+
# change the CAS value to be different than what #cas just loaded.
211+
# Do it every time so we just keep retrying and failing.
212+
connection.set(uniq_id, {"bar" => calls})
213+
214+
# Complete the modification we desire, which should fail when set.
215+
new_val["baz"] = 3
216+
new_val
217+
when :set
218+
assert ret.error.is_a? Couchbase::Error::KeyExists
219+
else
220+
flunk "Unexpected operation: #{ret.operation.inspect}"
221+
end
222+
end
223+
end
224+
assert_equal 12, calls
225+
end
226+
116227
def test_flags_replication
117228
connection = Couchbase.new(:hostname => @mock.host, :port => @mock.port,
118229
:default_format => :document)

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