I have a 30GB mongodb 3.6 collection with 500k documents. the main _id field is a float timestamp (i didnt manually define an index, but inserted on the _id field, assuming from documentation that _id will be used as index and automatically maintained.
Now if I query last data I do in Python 3
cursor = cry.find().sort('_id', pymongo.DESCENDING).limit(600)
df = list(cursor)
However, just querying the last 600 records takes about 1 minute. How can this be if the index is maintained? Is there a faster way to query (like by natural order) or do I need to re-index although documentation says its done automatically?
I also tried
cursor=cry.find().skip(cry.count() - 1000)
df = list(cursor)
but this is just as slow
