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

前段时间我用Python编写了MongoDB的增量备份工具。该工具通过拖尾oplog来监控数据更改。这是代码的相关部分。

更新了答案，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)

另见http://api.mongodb.com/python/current/examples/tailable.html。

原始回答，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

我今天遇到了这个问题，并没有在任何地方找到更新的答案。

Cursor类自v3.0起已更改，不再接受tailable和await_data参数。此示例将在发现记录 newer 而不是找到的最后一个记录时挂起oplog并打印oplog记录。

# Adapted from the example here: https://jira.mongodb.org/browse/PYTHON-735 # to work with pymongo 3.0 import pymongo from pymongo.cursor import CursorType c = pymongo.MongoClient() # Uncomment this for master/slave. oplog = c.local.oplog['$main'] # Uncomment this for replica sets. #oplog = c.local.oplog.rs first = next(oplog.find().sort('$natural', pymongo.DESCENDING).limit(-1)) ts = first['ts'] while True: cursor = oplog.find({'ts': {'$gt': ts}}, cursor_type=CursorType.TAILABLE_AWAIT, oplog_replay=True) while cursor.alive: for doc in cursor: ts = doc['ts'] print doc # Work with doc here

Answer 3

使用tailable cursor查询oplog。

实际上很有趣，因为oplog监控正是最初添加tailable-cursor功能的原因。我发现它对其他东西也非常有用（例如，实现基于mongodb的pubsub，例如参见this post），但这是最初的目的。

Answer 4

我有同样的问题。我把这个rescommunes/oplog.py放在一起。查看评论并查看__main__，了解如何在脚本中使用它。

Python如何观察Mongodb Oplog的变化

4 个答案: