1. Tips, Trick and Hacks Get’n it done!

2. Basic Expectations No transactions Fast-N-Loose by default (no safe/w/GLE) Indexing order matters; query optimizer helps One write thread One JS thread (M/R, $where, group) Many query threads (non-js) Memory Mapped Data Files BSON everywhere

3. Indexes Index on A, B, C works for [A], [A,B], [A,B,C] Query Optimizer figures out order Hint when you know Missing values are indexed as “null” value Just like real “null” values Unique indexes include missing/nulls Sort works on last field

4. Shell: Functions Leave off the () to see the function: > db.coll.find function (query, fields, limit, skip) { return new DBQuery(this._mongo, this._db, this, this._fullName, this._massageObject(query), fields, limit, skip); }

5. Connections Order of ops is only preserved in the same connection (socket/port) Connection pools are good, but could be a problem (getLastError/ordered ops) Server only executes one (concurrent) operation per connection

6. getLastError() More like getLastOpStatus() Returns useful data on update/findAndModify/insert/remove ops > db.t.update({x:1}, {$inc:{y:1}}, true, true) > db.getLastErrorObj() { "err" : null, "updatedExisting" : false, "upserted" : ObjectId("4c49f54cab620000000071b7"), "n" : 1, "ok" : 1 }

7. getLastErrorParams Params w: number of replicas to write to wtimeout: time to wait for acknowledgements fsync: flush to disk {getlasterror : 1, w : 40, wtimeout: 3000} { "err" : null, "n" : 0, "wtimeout" : true, "waited" : 3006, "errmsg" : "timed out waiting for slaves", "ok" : 0 }

8. Shell Command Line --eval it/cursor Printing values; be careful Pass in a script

9. Enable Profiling setProfilingLevel(lvl, <ms>) 0: none 1: time-based 2: all Reading from profile collection >db.system.profile.find()

10. _id: ObjectId Generated on Client Most drivers create “_id” field (if not set) No way to get “_id” after insert (from server) Nothing you can’t do yourself class Foo { ObjectId id = new ObjectId() …. }

11. mongod.conf Specify a logpath or it goes to /dev/null Quiet = true/anything Don’t do Quiet = false Flag options used no matter what values V[v*] = true for verbose logging

12. Limit/Sort/Pagination Sort fields should be the last in the index Limit helps with in-memory sorts (diff alg.) Skip/Offset still walks through index Pagination is best using last “_id”/sort value Set batchsize = pagesize (under 4MB)

13. Bulk Data Loading Initial load Create the index after load Start with new DB if possible Updates Be careful of excessive indexes Sometimes better to drop and recreate indexes

14. Printing Collection Stats db.getCollectionNames(). forEach(function(x){ print(“Collection: “ + x); printjson(db[x].stats()); })

15. Backups Only way to get a consistent state Don’t use mongoexport (lacks type fidelity) Use mongodump (snap-shotted query) Or fsync+copy 1.) fsync + lock 2.) backup dbpath files 3.) release lock

16. mongostat Watch % idx miss faults/sec flushes/sec

17. Questions You don’t have to go home, but you can’t… ScottHernandez@gmail.com