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MongoDB Drivers And High Availability: Deep Dive
- 1. MongoDB Drivers & High Availability A. Jesse Jiryu Davis Staff Engineer, MongoDB @jessejiryudavis
- 2. Client Side
- 3. • It’s a MongoDB driver specification. • (It’s not MMS.) • Written by me. Advisors: David Golden, Craig Wilson, Jeff Yemin. Overseen by Bernie Hackett. Server Discovery & Monitoring Spec
- 8. primary host1 secondary host2 secondary host3 Python Program monitor thread monitor thread MongoClient {secondary: true, hosts: ["host1", "host2", "host3"]} "mongodb://host1,host2/?replicaSet=my-rs"
- 9. ismaster (from secondary) {"setName": "rs-name",! "ismaster": false,! "secondary": true,! "hosts": ["host1", "host2", "host3"]}!
- 10. {"setName": "rs-name",! "ismaster": true,! "secondary": false,! "hosts": ["host1", "host2", "host3"]}! ismaster (from primary)
- 11. Updating Topology Description Current description + ismaster response → new description
- 13. primary host1 secondary host2 secondary host3 Python Program monitor thread monitor thread monitor thread MongoClient {secondary: true, hosts: ["host1", "host2", "host3"]} "new info!" Your Code? ✓
- 14. client.db.collection.insert({'my': 'document'})! client = MongoClient(! 'mongodb://host1,host2/?replicaSet=my-rs')!
- 15. primary host1 secondary host2 secondary host3 Python Program monitor thread monitor thread monitor thread MongoClient {ismaster: true, hosts: ["host1", "host2", "host3"]} {secondary: true, hosts: ["host1", "host2", "host3"]} Your Code insert ok ✓ ✓ "new info!" insert ok ✓
- 16. Steady State
- 18. Crisis
- 22. Resolution
- 23. primary host1 secondary host2 secondary host3 monitor thread monitor thread monitor thread Your Code ✓ insert "Wake up!" (every half second) MongoClient primary host2 ✓ insert ok ok Resolution ?
- 24. So What?
- 25. client = MongoClient(! 'mongodb://host1,host2/?replicaSet=my-rs')! ! try:! client.admin.command('ismaster')! except pymongo.errors.ConnectionFailure as e:! print("Can't connect: %s" % e)! Non-Blocking Client Construction #1
- 26. Error Handling #2 def find_my_document():! try:! return collection.find_one(query)! except ConnectionFailure:! logging.exception("finding document")! return collection.find_one(query)!
- 27. Error Handling #2 def insert_doc():! doc = {'_id': ObjectId(), 'a': 1}! try:! collection.insert(doc)! except ConnectionFailure:! logging.exception("inserting document")! # Try again.! collection.insert(doc)! except DuplicateKeyError:! # Previous try actually succeeded.! pass!
- 28. #2 Error Handling collection.update(! {'_id': 1},! {'$inc': {'counter': 1}})!
- 29. #2 Only idempotent operations can be retried Error Handling
- 31. ConnectionFailure! monitor thread monitor thread monitor thread primary host1 secondary host2 secondary host3 Your Code insert insertMongoClient "Wake up!" wait for connectTimeoutMS wait for serverSelectionTimeoutMS (30 seconds)