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  1. Core Server
  2. SERVER-29446

$sample stage could not find a non-duplicate document while using a random cursor

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    • Storage Engines
    • ALL
    • v4.2
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      Taken from Jesse's comment on SERVER-20385.

      With MongoDB 3.4.4 on Mac OS X, I can reproduce this. First do "python -m pip install pymongo pytz", then:

      from datetime import datetime, timedelta
 
import pytz
from bson import ObjectId
from pymongo import MongoClient
from pymongo.errors import OperationFailure
 
CHUNKS = 20
 
collection = MongoClient().db.test
collection.delete_many({})
 
start = datetime(2000, 1, 1, tzinfo=pytz.UTC)
for hour in range(10000):
    collection.insert(
        {'_id': ObjectId.from_datetime(start + timedelta(hours=hour)), 'x': 1})
 
for _ in range(10):
    try:
        docs = list(collection.aggregate([{
            "$sample": {"size": CHUNKS}
        }, {
            "$sort": {"_id": 1}
        }]))
    except OperationFailure as exc:
        if exc.code == 28799:
            # Work around https://jira.mongodb.org/browse/SERVER-20385
            print("retry")
            continue
 
        raise
 
    for d in docs:
        print(d['_id'].generation_time)
 
    break
else:
    raise OperationFailure("$sample failed")

      As often as not, the sample fails ten times in a row with error code 28799 and the message: "$sample stage could not find a non-duplicate document after 100 while using a random cursor. This is likely a sporadic failure, please try again."

      Show
      Taken from Jesse's comment on SERVER-20385 . With MongoDB 3.4.4 on Mac OS X, I can reproduce this. First do "python -m pip install pymongo pytz", then: from datetime import datetime, timedelta import pytz from bson import ObjectId from pymongo import MongoClient from pymongo.errors import OperationFailure CHUNKS = 20 collection = MongoClient().db.test collection.delete_many({}) start = datetime(2000, 1, 1, tzinfo=pytz.UTC) for hour in range (10000): collection.insert( { '_id' : ObjectId.from_datetime(start + timedelta(hours=hour)), 'x' : 1}) for _ in range (10): try : docs = list (collection.aggregate([{ "$sample" : { "size" : CHUNKS} }, { "$sort" : { "_id" : 1} }])) except OperationFailure as exc: if exc.code == 28799: # Work around https://jira.mongodb.org/browse/SERVER-20385 print ( "retry" ) continue raise for d in docs: print (d[ '_id' ].generation_time) break else : raise OperationFailure( "$sample failed" ) As often as not, the sample fails ten times in a row with error code 28799 and the message: "$sample stage could not find a non-duplicate document after 100 while using a random cursor. This is likely a sporadic failure, please try again."
    • Storage 2017-07-31, Storage Engines 2019-08-12, Storage Engines 2019-08-26, StorEng - 2023-08-08
    • 19

      The error originally reported in SERVER-20385 is marked as fixed in 3.1.9, but we are still able to reproduce it against version 3.4.4

            Assignee:
            backlog-server-storage-engines [DO NOT USE] Backlog - Storage Engines Team
            Reporter:
            charlie.swanson@mongodb.com Charlie Swanson
            Votes:
            2 Vote for this issue
            Watchers:
            30 Start watching this issue

              Created:
              Updated:
              Resolved: