Python如何观察Mongodb Oplog的变化 [英] How can Python Observe Changes to Mongodb's Oplog

问题描述

我有多个使用pyMongo编写到Mongodb的Python脚本.发生更改时，另一个Python脚本如何观察Mongo查询的更改并执行某些功能? mongodb已设置为启用oplog.

I have multiple Python scripts writing to Mongodb using pyMongo. How can another Python script observe changes to a Mongo query and perform some function when the change occurs? mongodb is setup with oplog enabled.

推荐答案

前段时间，我使用Python为MongoDB编写了增量备份工具.该工具通过尾随oplog监视数据更改.这是代码的相关部分.

I wrote a incremental backup tool for MongoDB some time ago, in Python. The tool monitors data changes by tailing the oplog. Here is the relevant part of the code.

更新后的答案，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)

另请参见 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()

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