python - Pymongo : how to ensure connection and reading from only desired host (especially SECONDARY) in a replica set -

background

mongodb production cluster (not sharded) 3 hosts. belong replica set rs0

• h1 - primary
• h2 - secondary
• h3 - secondary

i trying write python script using pymongo. being production cluster, want script read h3 secondary replica set not burden primary , keep free regular activities. data fetched collection called "devices" in batches of 2000 documents. should further reduce read operations overhead.

relevant code

client = mongoclient('mongodb://h3-hostname:27017/', replicaset='rs0', readpreference='secondary') . . . . . devices = devices_collection.find({"status" : "active"},{"key" : 1, "username" : 1}, sort = [("key", pymongo.ascending)]).batch_size(2000) 

also tried creating client in little different way mentioning hosts in cluster below

client = mongoclient('mongodb://h1-hostname:27017, h2-hostname:27017, h3-hostname:27017/?replicaset=rs0', readpreference='secondary') 

problem

as per understanding, above client read only secondary replica set. when run script , @ cloud manager, h1 primary shows page faults increased ~15-20 ~600 sharp jump.

environment

• mongo db 3.0.3 (mmapv1 storage engine)
• python 2.7.9
• pymongo 3.0.3
• os amazon linux

i posted problem mongo-user group, answered.

first of all, version of pymongo wrong. 2.8, @ least 1 python27 using

$ python27 >>> import pymongo >>> pymongo.version     '2.8' 

and

$ python >>> import pymongo >>> pymongo.version     '3.0.3' 

the appropriate syntax was

mongoclient('mongodb://h3-hostname:27017/?readpreference=secondary')