我正在尝试用 ruby 创建一个 oplog 观察器。到目前为止,我想出了下面的一个小脚本。
require 'rubygems'
require 'mongo'
db = Mongo::Connection.new("localhost", 5151).db("local")
coll = db.collection('oplog.$main')
loop do
cursor = Mongo::Cursor.new(coll, :tailable => true)
while not cursor.closed?
if doc = cursor.next_document
puts doc
else
sleep 1
end
end
end
问题是,5 或 6 秒后,当它吐出大量数据时,它会超时,并且出现错误
C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/connection.rb
:807:in `check_response_flags': Query response returned CURSOR_NOT_FOUND. Either an invalid c
ursor was specified, or the cursor may have timed out on the server. (Mongo::OperationFailure
)
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
connection.rb:800:in `receive_response_header'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
connection.rb:768:in `receive'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
connection.rb:493:in `receive_message'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
connection.rb:491:in `synchronize'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
connection.rb:491:in `receive_message'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
cursor.rb:494:in `send_get_more'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
cursor.rb:456:in `refresh'
from C:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/mongo-1.4.0/lib/../lib/mongo/
cursor.rb:124:in `next_document'
from n.rb:7
from n.rb:6:in `loop'
from n.rb:6
我不明白的是,当我能够看到实际数据时,它怎么会突然说找不到光标。我对 ruby 还很陌生,任何关于我必须采取的方向的想法对我来说都是有用的。
解决方案是我需要有一个异常处理机制来捕获当光标以每秒较高写入次数读取相对较小的 oplog 中的最后一个文档时引发的异常。由于游标到达 oplog 的末尾,它会抛出一个异常,表明没有更多记录。
require 'rubygems'
require 'mongo'
db = Mongo::Connection.new("localhost",5151).db("local")
coll = db.collection('oplog.$main')
loop do
cursor = Mongo::Cursor.new(coll, :timeout => false, :tailable => true)
while not cursor.closed?
begin
if doc = cursor.next_document
puts "Timestamp"
puts doc["ts"]
puts "Record"
puts doc["o"]
puts "Affected Collection"
puts doc["ns"]
end
rescue
puts ""
break
end
end
end
现在,当异常已被处理时,这可以正常工作。感谢 mongodb-user google group 向我指出了这一点。
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