Test
c = db.c;
c.drop();
c.update( { a:1 }, { $setOnInsert:{ a:2 } }, true );
Output
Wed Feb 20 13:51:16.234 [conn1] CMD: drop test.c
Wed Feb 20 13:51:31.011 [conn1] test.c Assertion failure false src/mongo/db/ops/update_internal.cpp 121
0x10bce9c55 0x10bcad16b 0x10bc8b829 0x10b8ba258 0x10b8d4bfa 0x10b8bfe2a 0x10b8c07cb 0x10b8c149f 0x10b8c1e23 0x10b8aed1a 0x10b8afdf0 0x10b7fa014 0x10b7ff73d 0x10b4032bf 0x10bcce910 0x10bcccee1 0x10bcccf46 0x10bcccf81 0x10bd5f439 0x7fff8514f8bf
0 mongod 0x000000010bce9c55 _ZN5mongo15printStackTraceERSo + 37
1 mongod 0x000000010bcad16b _ZN5mongo10logContextEPKc + 123
2 mongod 0x000000010bc8b829 _ZN5mongo12verifyFailedEPKcS1_j + 409
3 mongod 0x000000010b8ba258 _ZNK5mongo3Mod5applyERNS_15BSONBuilderBaseENS_11BSONElementERNS_8ModStateE + 352
4 mongod 0x000000010b8d4bfa _ZN5mongo8ModState5applyERNS_15BSONBuilderBaseENS_11BSONElementE + 74
5 mongod 0x000000010b8bfe2a _ZN5mongo11ModSetState17createNewFromModsERKSsRNS_15BSONBuilderBaseERNS_18BSONIteratorSortedERKSt4pairIKSt17_Rb_tree_iteratorIS7_IS1_N5boost10shared_ptrINS_8ModStateEEEEESF_ERKNS_9LexNumCmpE + 5618
6 mongod 0x000000010b8c07cb _ZN5mongo11ModSetState20createNewObjFromModsERKSsRNS_14BSONObjBuilderERKNS_7BSONObjE + 167
7 mongod 0x000000010b8c149f _ZN5mongo11ModSetState17createNewFromModsEv + 181
8 mongod 0x000000010b8c1e23 _ZN5mongo6ModSet18createNewFromQueryERKNS_7BSONObjE + 1767
9 mongod 0x000000010b8aed1a _ZN5mongo14_updateObjectsEbPKcRKNS_7BSONObjES4_bbbRNS_7OpDebugEPNS_11RemoveSaverEbRKNS_24QueryPlanSelectionPolicyEb + 11642
10 mongod 0x000000010b8afdf0 _ZN5mongo13updateObjectsEPKcRKNS_7BSONObjES4_bbbRNS_7OpDebugEbRKNS_24QueryPlanSelectionPolicyE + 224
11 mongod 0x000000010b7fa014 _ZN5mongo14receivedUpdateERNS_7MessageERNS_5CurOpE + 2052
12 mongod 0x000000010b7ff73d _ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE + 2445
13 mongod 0x000000010b4032bf _ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE + 261
14 mongod 0x000000010bcce910 _ZN5mongo17PortMessageServer17handleIncomingMsgEPv + 2384
15 mongod 0x000000010bcccee1 _ZN5boost3_bi5list1INS0_5valueIPN5mongo17PortMessageServer22HandleIncomingMsgParamEEEEclIPvPFSA_SA_ENS0_5list0EEET_NS0_4typeISE_EERT0_RT1_l + 79
16 mongod 0x000000010bcccf46 _ZN5boost3_bi6bind_tIPvPFS2_S2_ENS0_5list1INS0_5valueIPN5mongo17PortMessageServer22HandleIncomingMsgParamEEEEEEclEv + 82
17 mongod 0x000000010bcccf81 _ZN5boost6detail11thread_dataINS_3_bi6bind_tIPvPFS4_S4_ENS2_5list1INS2_5valueIPN5mongo17PortMessageServer22HandleIncomingMsgParamEEEEEEEE3runEv + 37
18 mongod 0x000000010bd5f439 thread_proxy + 169
19 libsystem_c.dylib 0x00007fff8514f8bf _pthread_start + 335
Wed Feb 20 13:51:31.060 [conn1] update test.c query: { a: 1.0 } update: { $setOnInsert: { a: 2.0 } } nscanned:0 keyUpdates:0 exception: assertion src/mongo/db/ops/update_internal.cpp:121 locks(micros) w:50020 50ms