data creation using createTestData("test", 10000, 20, 4, 20); -->

olivers-mbp-4:Duplicate Oliver$ mongo localhost:27017/local BugRep.js
MongoDB shell version: 2.6.5
connecting to: localhost:27017/local
createTestData...
createCollection...
base size: 394537
aggregation...
agg size: 0

Log:

2014-12-09T16:31:29.587+0100 [initandlisten] connection accepted from 127.0.0.1:51865 #18 (13 connections now open)
2014-12-09T16:31:35.281+0100 [conn18] remove local.base ndeleted:392404 keyUpdates:0 numYields:23 locks(micros) w:4912555 2596ms
2014-12-09T16:31:35.281+0100 [conn18] command local.$cmd command: delete { delete: "base", deletes: [ { q: {}, limit: 0.0 } ], ordered: true } keyUpdates:0 numYields:0  reslen:40 2596ms
2014-12-09T16:31:47.005+0100 [conn18] build index on: local.tmp.agg_out.6 properties: { v: 1, key: { _id: 1 }, name: "_id_", ns: "local.tmp.agg_out.6" }
2014-12-09T16:31:47.005+0100 [conn18] 	 added index to empty collection
2014-12-09T16:31:48.465+0100 [conn18] warning: DR102 too much data written uncommitted 314.577MB
2014-12-09T16:31:50.139+0100 [conn18] local.tmp.agg_out.6 warning assertion failure _intents.size() < 2000000 src/mongo/db/dur_commitjob.h 112
2014-12-09T16:31:50.142+0100 [conn18] local.tmp.agg_out.6 0x103b045aa 0x103aaf135 0x103a9b87a 0x10354baa3 0x10354b5f7 0x1035475e9 0x103622635 0x10361f5d6 0x10361c65f 0x103623362 0x10335e00e 0x1036e6b1d 0x1036e6ff2 0x10373c2f1 0x1034bf0b1 0x103518aa9 0x10351a356 0x10351b92c 0x10378371e 0x10361b0b7
 0   mongod                              0x0000000103b045aa _ZN5mongo15printStackTraceERNSt3__113basic_ostreamIcNS0_11char_traitsIcEEEE + 58
 1   mongod                              0x0000000103aaf135 _ZN5mongo10logContextEPKc + 453
 2   mongod                              0x0000000103a9b87a _ZN5mongo9wassertedEPKcS1_j + 810
 3   mongod                              0x000000010354baa3 _ZN5mongo3dur9CommitJob4noteEPvi + 851
 4   mongod                              0x000000010354b5f7 _ZN5mongo3dur18ThreadLocalIntents7unspoolEv + 103
 5   mongod                              0x00000001035475e9 _ZN5mongo3dur11DurableImpl14commitIfNeededEb + 41
 6   mongod                              0x0000000103622635 _ZN5mongo11insertMultiERNS_6Client7ContextEbPKcRNSt3__16vectorINS_7BSONObjENS5_9allocatorIS7_EEEERNS_5CurOpE + 165
 7   mongod                              0x000000010361f5d6 _ZN5mongo14receivedInsertERNS_7MessageERNS_5CurOpE + 2070
 8   mongod                              0x000000010361c65f _ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE + 8207
 9   mongod                              0x0000000103623362 _ZN5mongo14DBDirectClient3sayERNS_7MessageEbPNSt3__112basic_stringIcNS3_11char_traitsIcEENS3_9allocatorIcEEEE + 162
 10  mongod                              0x000000010335e00e _ZN5mongo12DBClientBase6insertERKNSt3__112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEERKNS1_6vectorINS_7BSONObjENS5_ISB_EEEEi + 622
 11  mongod                              0x00000001036e6b1d _ZN5mongo17DocumentSourceOut5spillEPNS_12DBClientBaseERKNSt3__16vectorINS_7BSONObjENS3_9allocatorIS5_EEEE + 29
 12  mongod                              0x00000001036e6ff2 _ZN5mongo17DocumentSourceOut7getNextEv + 802
 13  mongod                              0x000000010373c2f1 _ZN5mongo8Pipeline3runERNS_14BSONObjBuilderE + 193
 14  mongod                              0x00000001034bf0b1 _ZN5mongo15PipelineCommand3runERKNSt3__112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEERNS_7BSONObjEiRS7_RNS_14BSONObjBuilderEb + 2721
 15  mongod                              0x0000000103518aa9 _ZN5mongo12_execCommandEPNS_7CommandERKNSt3__112basic_stringIcNS2_11char_traitsIcEENS2_9allocatorIcEEEERNS_7BSONObjEiRS8_RNS_14BSONObjBuilderEb + 41
 16  mongod                              0x000000010351a356 _ZN5mongo7Command11execCommandEPS0_RNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb + 4678
 17  mongod                              0x000000010351b92c _ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi + 1420
 18  mongod                              0x000000010378371e _ZN5mongo11newRunQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1_ + 1230
 19  mongod                              0x000000010361b0b7 _ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE + 2663
2014-12-09T16:31:50.368+0100 [conn18] insert local.tmp.agg_out.6 ninserted:304717 keyUpdates:0 numYields:0 locks(micros) w:1987786 1988ms
2014-12-09T16:31:50.838+0100 [conn18] CMD: drop local.tmp.agg_out.6
2014-12-09T16:31:50.839+0100 [conn18] command local.$cmd command: aggregate { aggregate: "base", pipeline: [ { $group: { _id: "$name", refs: { $addToSet: "$ref" } } }, { $out: "agg" } ], allowDiskUse: true } keyUpdates:0 numYields:20 locks(micros) R:431996 r:230533 reslen:164 3834ms