Python如何观察Mongodb Oplog的变化

Question

我有多个Python脚本使用pyMongo写入Mongodb.另一个Python脚本如何观察Mongo查询的更改并在发生更改时执行某些功能？设置了启用oplog的mongodb.

Answer 1

我在前一段时间用Python编写了MongoDB的增量备份工具.该工具通过拖尾来监控数据变化oplog.这是代码的相关部分.

更新的答案,pymongo 3

from time import sleep

from pymongo import MongoClient, ASCENDING
from pymongo.cursor import CursorType
from pymongo.errors import AutoReconnect

# Time to wait for data or connection.
_SLEEP = 1.0

if __name__ == '__main__':
    oplog = MongoClient().local.oplog.rs
    stamp = oplog.find().sort('$natural', ASCENDING).limit(-1).next()['ts']

    while True:
        kw = {}

        kw['filter'] = {'ts': {'$gt': stamp}}
        kw['cursor_type'] = CursorType.TAILABLE_AWAIT
        kw['oplog_replay'] = True

        cursor = oplog.find(**kw)

        try:
            while cursor.alive:
                for doc in cursor:
                    stamp = doc['ts']

                    print(doc)  # Do something with doc.

                sleep(_SLEEP)

        except AutoReconnect:
            sleep(_SLEEP)

另请参阅http://api.mongodb.com/python/current/examples/tailable.html.

原始答案,pymongo 2

from time import sleep

from pymongo import MongoClient
from pymongo.cursor import _QUERY_OPTIONS
from pymongo.errors import AutoReconnect
from bson.timestamp import Timestamp

# Tailable cursor options.
_TAIL_OPTS = {'tailable': True, 'await_data': True}

# Time to wait for data or connection.
_SLEEP = 10

if __name__ == '__main__':
    db = MongoClient().local

    while True:
        query = {'ts': {'$gt': Timestamp(some_timestamp, 0)}}  # Replace with your query.
        cursor = db.oplog.rs.find(query, **_TAIL_OPTS)

        cursor.add_option(_QUERY_OPTIONS['oplog_replay'])

        try:
            while cursor.alive:
                try:
                    doc = next(cursor)

                    # Do something with doc.

                except (AutoReconnect, StopIteration):
                    sleep(_SLEEP)

        finally:
            cursor.close()

Answer 2

使用可尾游标查询 oplog 。

这实际上很有趣，因为 oplog 监控正是最初添加 tailable-cursor 功能的目的。我发现它对于其他事情也非常有用（例如实现基于 mongodb 的 pubsub，例如参见这篇文章），但这就是最初的目的。