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 And its going to be awesome! 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 does t heobservation 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 / @jonnyeight Senior Director of Performance Engineering, MongoDB Alvin Richards #MongoDBWorld Thank You