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Second attempt which removes any kind proxying.

This commit is contained in:
Guo Xiang Tan 2016-01-26 15:46:51 +08:00
parent 46589a1a0c
commit 0058d09e35
3 changed files with 72 additions and 128 deletions
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8
config/database.yml
View File

@ -1,13 +1,7 @@
development:
prepared_statements: false
adapter: postgresql_fallback
host: 172.17.0.2
port: 6432
adapter: postgresql
database: discourse_development
username: tgxworld
password: test
replica_host: 172.17.0.3
replica_port: 6432
min_messages: warning
pool: 5
timeout: 5000

114
lib/active_record/connection_adapters/postgresql_fallback_adapter.rb
View File

@ -14,7 +14,7 @@ class TaskObserver
logger.info { "PG connection heartbeat: Master connection is not active.".freeze }
else
logger.error { "PG connection heartbeat failed with error: \"#{ex}\"" }
end
end
end
end
@ -28,15 +28,21 @@ end
module ActiveRecord
module ConnectionHandling
def postgresql_fallback_connection(config)
master_connection = postgresql_connection(config)
begin
connection = postgresql_connection(config)
rescue PG::ConnectionBad => e
connection = postgresql_connection(config.dup.merge({
"host" => config["replica_host"], "port" => config["replica_port"]
}))
replica_connection = postgresql_connection(config.dup.merge({
host: config[:replica_host], port: config[:replica_port]
}))
verify_replica(replica_connection)
verify_replica(connection)
klass = ConnectionAdapters::PostgreSQLFallbackAdapter.proxy_pass(master_connection.class)
klass.new(master_connection, replica_connection, logger, config)
Discourse.enable_readonly_mode if !Discourse.readonly_mode?
start_connection_heartbeart(connection, config)
end
connection
end
private
@ -45,92 +51,24 @@ module ActiveRecord
value = connection.raw_connection.exec("SELECT pg_is_in_recovery()").values[0][0]
raise "Replica database server is not in recovery mode." if value == 'f'
end
end
module ConnectionAdapters
class PostgreSQLFallbackAdapter < AbstractAdapter
ADAPTER_NAME = "PostgreSQLFallback".freeze
MAX_FAILURE = 5
HEARTBEAT_INTERVAL = 5
def interval
5
end
attr_reader :main_connection
def start_connection_heartbeart(existing_connection, config)
timer_task = Concurrent::TimerTask.new(execution_interval: interval) do |task|
connection = postgresql_connection(config)
def self.all_methods(klass)
methods = []
(klass.ancestors - AbstractAdapter.ancestors).each do |_klass|
%w(public protected private).map do |level|
methods << _klass.send("#{level}_instance_methods", false)
end
end
methods.flatten.uniq.sort
end
def self.proxy_pass(klass)
Class.new(self) do
(self.all_methods(klass) - self.all_methods(self)).each do |method|
self.class_eval <<-EOF
def #{method}(*args, &block)
proxy_method(:#{method}, *args, &block)
end
EOF
end
if connection.active?
existing_connection.disconnect!
Discourse.disable_readonly_mode if Discourse.readonly_mode?
task.shutdown
end
end
def initialize(master_connection, replica_connection, logger, config)
super(nil, logger, config)
@master_connection = master_connection
@main_connection = @master_connection
@replica_connection = replica_connection
@failure_count = 0
load!
end
def proxy_method(method, *args, &block)
@main_connection.send(method, *args, &block)
rescue ActiveRecord::StatementInvalid => e
if e.message.include?("PG::UnableToSend") && @main_connection == @master_connection
@failure_count += 1
if @failure_count == MAX_FAILURE
Discourse.enable_readonly_mode if !Discourse.readonly_mode?
@main_connection = @replica_connection
load!
connection_heartbeart(@master_connection)
@failure_count = 0
else
proxy_method(method, *args, &block)
end
end
raise e
end
private
def load!
@visitor = @main_connection.visitor
@connection = @main_connection.raw_connection
end
def connection_heartbeart(connection, interval = HEARTBEAT_INTERVAL)
timer_task = Concurrent::TimerTask.new(execution_interval: interval) do |task|
connection.reconnect!
if connection.active?
@main_connection = connection
load!
Discourse.disable_readonly_mode if Discourse.readonly_mode?
task.shutdown
end
end
timer_task.add_observer(TaskObserver.new)
timer_task.execute
end
timer_task.add_observer(TaskObserver.new)
timer_task.execute
end
end
end

78
spec/components/active_record/connection_adapters/postgresql_fallback_adapter_spec.rb
View File

@ -1,55 +1,67 @@
require 'rails_helper'
require_dependency 'active_record/connection_adapters/postgresql_fallback_adapter'
describe ActiveRecord::ConnectionAdapters::PostgreSQLFallbackAdapter do
let(:master_connection) { ActiveRecord::Base.connection }
let(:replica_connection) { master_connection.dup }
let(:adapter) { described_class.new(master_connection, replica_connection, nil, nil) }
before :each do
ActiveRecord::Base.clear_all_connections!
describe ActiveRecord::ConnectionHandling do
let(:config) do
ActiveRecord::Base.configurations["test"].merge({
"adapter" => "postgresql_fallback",
"replica_host" => "localhost",
"replica_port" => "6432"
})
end
describe "proxy_method" do
context "when master connection is not active" do
after do
ActiveRecord::Base.clear_all_connections!
Discourse.disable_readonly_mode
end
describe "#postgresql_fallback_connection" do
it 'should return a PostgreSQL adapter' do
expect(ActiveRecord::Base.postgresql_fallback_connection(config))
.to be_an_instance_of(ActiveRecord::ConnectionAdapters::PostgreSQLAdapter)
end
context 'when master server is down' do
before do
replica_connection.stubs(:send)
master_connection.stubs(:send).raises(ActiveRecord::StatementInvalid.new('PG::UnableToSend'))
master_connection.stubs(:reconnect!)
master_connection.stubs(:active?).returns(false)
@replica_connection = mock('replica_connection')
@old_const = described_class::HEARTBEAT_INTERVAL
described_class.const_set("HEARTBEAT_INTERVAL", 0.1)
ActiveRecord::Base.expects(:postgresql_connection).with(config).raises(PG::ConnectionBad)
ActiveRecord::Base.expects(:postgresql_connection).with(config.merge({
"host" => "localhost", "port" => "6432"
})).returns(@replica_connection)
ActiveRecord::Base.expects(:verify_replica).with(@replica_connection)
@replica_connection.expects(:disconnect!)
ActiveRecord::Base.stubs(:interval).returns(0.1)
Concurrent::TimerTask.any_instance.expects(:shutdown)
end
after do
Discourse.disable_readonly_mode
described_class.const_set("HEARTBEAT_INTERVAL", @old_const)
end
it 'should failover to a replica server' do
ActiveRecord::Base.postgresql_fallback_connection(config)
it "should set site to readonly mode and carry out failover and switch back procedures" do
expect(adapter.main_connection).to eq(master_connection)
adapter.proxy_method('some method')
expect(Discourse.readonly_mode?).to eq(true)
expect(adapter.main_connection).to eq(replica_connection)
master_connection.stubs(:active?).returns(true)
ActiveRecord::Base.unstub(:postgresql_connection)
sleep 0.15
expect(Discourse.readonly_mode?).to eq(false)
expect(adapter.main_connection).to eq(master_connection)
expect(ActiveRecord::Base.connection)
.to be_an_instance_of(ActiveRecord::ConnectionAdapters::PostgreSQLAdapter)
end
end
it 'should raise errors not related to the database connection' do
master_connection.stubs(:send).raises(StandardError.new)
expect { adapter.proxy_method('some method') }.to raise_error(StandardError)
end
context 'when both master and replica server is down' do
it 'should raise the right error' do
ActiveRecord::Base.expects(:postgresql_connection).raises(PG::ConnectionBad).twice
it 'should proxy methods successfully' do
expect(adapter.proxy_method(:execute, 'SELECT 1').values[0][0]).to eq("1")
expect(adapter.proxy_method(:active?)).to eq(true)
expect(adapter.proxy_method(:raw_connection)).to eq(master_connection.raw_connection)
expect { ActiveRecord::Base.postgresql_fallback_connection(config) }
.to raise_error(PG::ConnectionBad)
end
end
end
end