1. Senior Director of Performance Engineering, MongoDB Alvin Richards #MongoDBWorld Mythbusting: Understanding How We Measure the Performance of MongoDB

2. Before we start We are going to look a lot at C++ kernel code Java benchmarks JavaScript tests And lots of charts

3. Measuring "Performance" https://www.youtube.com/watch?v=7wm-pZp_mi0

4. Benchmarking Some common traps Performance measurement & diagnosis What's next

5. Part One Some Common Traps

6. The Milk Train Doesn't Stop Here Anymore Tennessee Williams "We all live in a house on fire, no fire department to call; no way out, just the upstairs window to look out of while the fire burns the house down with us trapped, locked in it."

7. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); #1 Time taken to Insert x Documents

8. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); #1 Time taken to Insert x Documents

9. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); #1 Time taken to Insert x Documents

10. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); #1 Time taken to Insert x Documents

11. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); #1 Time taken to Insert x Documents

12. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); So that looks ok, right?

13. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); What are else you measuring? Object creation and GC management?

14. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); What are else you measuring? Thread contention on nextInt()? Object creation and GC management?

15. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); What are else you measuring? Time to synthesize data? Object creation and GC management? Thread contention on nextInt()?

16. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); What are else you measuring? Object creation and GC management? Thread contention on addAndGet()? Thread contention on nextInt()? Time to synthesize data?

17. long startTime = System.currentTimeMillis(); for (int roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; BasicDBObject doc = new BasicDBObject(); doc.put("_id",id); doc.put("k",rand.nextInt(numMaxInserts)+1); String cVal = "" doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i]=doc; } coll.insert(aDocs); numInserts += documentsPerInsert; globalInserts.addAndGet(documentsPerInsert); } long endTime = System.currentTimeMillis(); What are else you measuring? Object creation and GC management? Clock resolution? Thread contention on nextInt()? Time to synthesize data? Thread contention on addAndGet()?

18. // Pre Create the Object outside the Loop BasicDBObject[] aDocs = new BasicDBObject[documentsPerInsert]; for (int i=0; i < documentsPerInsert; i++) { BasicDBObject doc = new BasicDBObject(); String cVal = ""; doc.put("c",cVal); String padVal = ""; doc.put("pad",padVal); aDocs[i] = doc; } Solution: Pre-Create the objects Pre-create non varying data outside the timing loop Alternative Pre-create the data in a file; load from file

19. // Use ThreadLocalRandom generator or an instance of java.util.Random per thread java.util.concurrent.ThreadLocalRandom rand; for (long roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; doc = aDocs[i]; doc.put("_id",id); doc.put("k", nextInt(rand, numMaxInserts)+1); } coll.insert(aDocs); numInserts += documentsPerInsert; } // Maintain count outside the loop globalInserts.addAndGet(documentsPerInsert * roundNum); Solution: Remove contention Remove contention nextInt() by making Thread local

20. // Use ThreadLocalRandom generator or an instance of java.util.Random per thread java.util.concurrent.ThreadLocalRandom rand; for (long roundNum = 0; roundNum < numRounds; roundNum++) { for (int i = 0; i < documentsPerInsert; i++) { id++; doc = aDocs[i]; doc.put("_id",id); doc.put("k", nextInt(rand, numMaxInserts)+1); } coll.insert(aDocs); numInserts += documentsPerInsert; } // Maintain count outside the loop globalInserts.addAndGet(documentsPerInsert * roundNum); Solution: Remove contention Remove contention on addAndGet() Remove contention nextInt() by making Thread local

21. long startTime = System.currentTimeMillis(); long endTime = System.currentTimeMillis(); long startTime = System.nanoTime(); long endTime = System.nanoTime() - startTime; Solution: Timer resolution "resolution is at least as good as that of currentTimeMillis()" "granularity of the value depends on the underlying operating system and may be larger" Source http://docs.oracle.com/javase/7/docs/api/java/lang/System.html

22. General Principal #1 Know what you are measuring

23. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); #2 Response time to return all results

24. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); #2 Response time to return all results

25. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); #2 Response time to return all results

26. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); #2 Response time to return all results

27. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); So that looks ok, right?

28. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); What are else you measuring? Each doc is is 4080 bytes on disk with powerOf2Sizes

29. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); What are else you measuring? Each doc is is 4080 bytes on disk with powerOf2Sizes Unrestricted predicate?

30. BasicDBObject doc = new BasicDBObject(); doc.put("v", str); // str is a 2k string for (int i=0; i < 1000; i++) { doc.put("_id",i); coll.insert(doc); } BasicDBObject predicate = new BasicDBObject(); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); What are else you measuring? Each doc is is 4080 bytes on disk with powerOf2Sizes Measuring Time to parse & execute query Time to retrieve all document But also Cost of shipping ~4MB data through network stack Unrestricted predicate?

31. BasicDBObject predicate = new BasicDBObject(); predicate.put("_id", new BasicDBObject("$gte", 10).append("$lte", 20)); BasicDBObject projection = new BasicDBObject(); projection.put("_id", 1); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate, projection ); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); Solution: Limit the projection Return fixed range

32. BasicDBObject predicate = new BasicDBObject(); predicate.put("_id", new BasicDBObject("$gte", 10).append("$lte", 20)); BasicDBObject projection = new BasicDBObject(); projection.put("_id", 1); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate, projection ); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); Solution: Limit the projection Only project _id Return fixed range

33. BasicDBObject predicate = new BasicDBObject(); predicate.put("_id", new BasicDBObject("$gte", 10).append("$lte", 20)); BasicDBObject projection = new BasicDBObject(); projection.put("_id", 1); long startTime = System.currentTimeMillis(); DBCursor cur = coll.find(predicate, projection ); DBObject foundObj; while (cur.hasNext()) { foundObj = cur.next(); } long endTime = System.currentTimeMillis(); Solution: Limit the projection Only project _id Only 46k transferred through network stack Return fixed range

34. General Principal #2 Measure only what you need to measure

35. Part Two Performance measurement & diagnosis

36. The Physical Principles of the Quantum Theory (1930) Werner Heisenberg "Every experiment destroys some of the knowledge of the system which was obtained by previous experiments."

37. Broad categories Micro Benchmarks Workloads

38. Micro benchmarks: mongo-perf

39. mongo-perf: goals Measure commands Configure Single mongod, ReplSet size (1 -> n), Sharding Single vs. Multiple DB O/S Characterize Throughput by thread count Compare

40. What do you get? Better

41. What do you get? Measured improvement between rc0 and rc2 Better

42. tests.push( { name: "Commands.CountsIntIDRange", pre: function( collection ) { collection.drop(); for ( var i = 0; i < 1000; i++ ) { collection.insert( { _id : i } ); } collection.getDB().getLastError(); }, ops: [ { op: "command", ns : "testdb", command : { count : "mycollection", query : { _id : { "$gt" : 10, "$lt" : 100 } } } } ] } ); Benchmark source code

43. tests.push( { name: "Commands.CountsIntIDRange", pre: function( collection ) { collection.drop(); for ( var i = 0; i < 1000; i++ ) { collection.insert( { _id : i } ); } collection.getDB().getLastError(); }, ops: [ { op: "command", ns : "testdb", command : { count : "mycollection", query : { _id : { "$gt" : 10, "$lt" : 100 } } } } ] } ); Benchmark source code

44. tests.push( { name: "Commands.CountsIntIDRange", pre: function( collection ) { collection.drop(); for ( var i = 0; i < 1000; i++ ) { collection.insert( { _id : i } ); } collection.getDB().getLastError(); }, ops: [ { op: "command", ns : "testdb", command : { count : "mycollection", query : { _id : { "$gt" : 10, "$lt" : 100 } } } } ] } ); Benchmark source code

45. tests.push( { name: "Commands.CountsIntIDRange", pre: function( collection ) { collection.drop(); for ( var i = 0; i < 1000; i++ ) { collection.insert( { _id : i } ); } collection.getDB().getLastError(); }, ops: [ { op: "command", ns : "testdb", command : { count : "mycollection", query : { _id : { "$gt" : 10, "$lt" : 100 } } } } ] } ); Benchmark source code

46. Code Change

47. Workloads "public" workloads YCSB Sysbench "real world" simulations Inbox fan in/out Message Stores Content Management

48. Example: Bulk Load Performance 16m Documents Better 55% degradation 2.6.0-rc1 vs 2.4.10

49. Ouch where's the tree in the woods? 2.4.10 -> 2.6.0 4495 git commits

50. git-bisect Bisect between good/bad hashes git-bisect nominates a new githash Build against githash Re-run test Confirm if this githash is good/bad Rinse and repeat

51. Code Change - Bad Githash

52. Code Change - Fix

53. Bulk Load Performance - Fix Better 11% improvement 2.6.1 vs 2.4.10

54. The problem with measurement Observability What can you observe on the system? Effect What effects can an observation cause?

55. mtools

56. mtools MongoDB log file analysis Filter logs for operations, events Response time, lock durations Plot https://github.com/rueckstiess/mtools

57. Response Times > 100ms Bulk Insert 2.6.0-rc0 Ops/Sec Time

58. Response Times > 100ms Bulk Insert 2.6.0-rc0 vs. 2.6.0-rc2 Floor raised

59. Code Change Yielding Policy

60. Code Change

61. Response Times Bulk Insert 2.6.0 vs 2.6.1 Ceiling similar, lower floor resulting in 40% improvement in throughput

62. Secondary effects of Yield policy change Write lock time reduced Order of magnitude reduction of write lock duration

63. > db.serverStatus() Yes will cause a read lock to be acquired > db.serverStatus({recordStats:0}) No lock is not acquired > mongostat Yes - until SERVER-14008 resolved, uses db.serverStatus() Unexpected side effects of measurement?

64. CPU sampling Get an impression of Call Graphs CPU time spent on node and called nodes

65. > sudo apt-get install google-perftools > sudo apt-get install libunwind7-dev > scons --use-cpu-profiler mongod Setup & building with google- profiler

66. > mongodb dbpath Note: Do not use fork > mongo > use admin > db.runCommand({_cpuProfilerStart: {profileFilename: 'foo.prof'}}) Execute some commands that you want to profile > db.runCommand({_cpuProfilerStop: 1}) Start the profiling

67. Sample start vs. end of workload

68. Sample start vs. end of workload

69. Code change

70. Public Benchmarks Not all forks are the same YCSB https://github.com/achille/YCSB sysbench-mongodb https://github.com/mdcallag/sysbench-mongodb

71. Part Three And next?

72. Beavis & Butthead "The future sucks. Change it." "I'm way cool Beavis, but I cannot change the future."

73. What we are working on mongo-perf UI refactor Adding more micro benchmarks Workloads Adding external benchmarks Creating benchmarks for common use cases Inbox fan in/out Analytical dashboards Stream / Feeds Customers, Partners & Community

74. Here's how you can help change the future! Got a great workload? Great benchmark? Want to donate it? alvin@mongodb.com

75. Don't be that benchmark #1 Know what you are measuring #2 Measure only what you need to measure

76. alvin@mongodb.com Senior Director of Performance Engineering, MongoDB Alvin Richards #MongoDBWorld Thank You