Motor Tailable Cursor Example

By default, MongoDB will automatically close a cursor when the client has exhausted all results in the cursor. However, for capped collections you may use a tailable cursor that remains open after the client exhausts the results in the initial cursor.

The following is a basic example of using a tailable cursor to tail the oplog of a replica set member:

from asyncio import sleep
from pymongo.cursor import CursorType

async def tail_oplog_example():
    oplog =
    first = await oplog.find().sort("$natural", pymongo.ASCENDING).limit(-1).next()
    ts = first["ts"]

    while True:
        # For a regular capped collection CursorType.TAILABLE_AWAIT is the
        # only option required to create a tailable cursor. When querying the
        # oplog, the oplog_replay option enables an optimization to quickly
        # find the 'ts' value we're looking for. The oplog_replay option
        # can only be used when querying the oplog. Starting in MongoDB 4.4
        # this option is ignored by the server as queries against the oplog
        # are optimized automatically by the MongoDB query engine.
        cursor = oplog.find(
            {"ts": {"$gt": ts}},
        while cursor.alive:
            async for doc in cursor:
                ts = doc["ts"]
            # We end up here if the find() returned no documents or if the
            # tailable cursor timed out (no new documents were added to the
            # collection for more than 1 second).
            await sleep(1)

See also

Tailable cursors