Hide
Here is a minimal jstest that produces the inaccurate sums:
(function() {
"use strict";
const coll = db.sums;
coll.drop();
const documentList = [
{
_id: 100,
"num": NumberLong("45103"),
},
{
_id: 101,
"num": NumberInt(42780),
},
{
_id: 102,
"num": NumberDecimal("100.111111111111111"),
},
];
documentList.forEach(doc => assert.commandWorked(coll.insert(doc)));
print(JSON.stringify(
coll.aggregate([
{$project: {"test": {$add: ["$num", NumberLong("9223372036854775807"), 44249]}}}
])
));
})();
When this test is run with SBE enabled, the printed output is:
{"_batch":[
{"_id":102,"test":{"$numberDecimal":"9223372036854820100.111111111111111"}},
{"_id":101,"test":9223372036854864000},
{"_id":100,"test":9223372036854866000}
],
"_cursorid":{"$numberLong":"0"},
"_ns":"test.sums",
"_db":{"_mongo":{"slaveOk":false,"host":"localhost:20000","defaultDB":"test","_defaultSession":{"_serverSession":{"handle":{}},"_isExplicit":false}},
"_name":"test","_session":{}},
"_collName":"sums","_cursorHandle":{}
}
This shows the final sums as
9223372036854866000,
9223372036854864000, and
9223372036854820100.111111111111111.
The real sum of these numbers is 9223372036854775807 + 44249 = 9223372036854820056, and adding the numbers in each of the documents respectively, the sums should be:
9223372036854865159,
9223372036854862836, and
9223372036854820156.111111111111111 respectively.
It appears to be rounding to (not necessarily the nearest) thousand, and, in the final case where $num is a NumberDecimal, simply adding the value of $num afterwards.
When the test is run with SBE disabled, the output is:
{"_batch":[
{"_id":102,"test":{"$numberDecimal":"9223372036854820964.111111111111111"}},
{"_id":101,"test":9223372036854864000},
{"_id":100,"test":9223372036854866000}
],
"_cursorid":{"$numberLong":"0"},"_ns":"test.sums","_db":{"_mongo":{"slaveOk":false,"host":"localhost:20000","defaultDB":"test","_defaultSession":{"_serverSession":{"handle":{}},"_isExplicit": false}},"_name":"test","_session":{}},"_collName":"sums","_cursorHandle":{}
}
In this case, the sums for documents 100 and 101 are the same, but the sum for document 102 is:
9223372036854820964.111111111111111
which is exactly 864 higher than what the other engine had. In fact, whenever $num is a NumberDecimal, the outcomes with SBE enabled or disabled have a difference of exactly 864.
Show
Here is a minimal jstest that produces the inaccurate sums:
(function() {
"use strict" ;
const coll = db.sums;
coll.drop();
const documentList = [
{
_id: 100,
"num" : NumberLong( "45103" ),
},
{
_id: 101,
"num" : NumberInt(42780),
},
{
_id: 102,
"num" : NumberDecimal( "100.111111111111111" ),
},
];
documentList.forEach(doc => assert .commandWorked(coll.insert(doc)));
print(JSON.stringify(
coll.aggregate([
{$project: { "test" : {$add: [ "$num" , NumberLong( "9223372036854775807" ), 44249]}}}
])
));
})();
When this test is run with SBE enabled, the printed output is:
{ "_batch" :[
{ "_id" :102, "test" :{ "$numberDecimal" : "9223372036854820100.111111111111111" }},
{ "_id" :101, "test" :9223372036854864000},
{ "_id" :100, "test" :9223372036854866000}
],
"_cursorid" :{ "$numberLong" : "0" },
"_ns" : "test.sums" ,
"_db" :{ "_mongo" :{ "slaveOk" : false , "host" : "localhost:20000" , "defaultDB" : "test" , "_defaultSession" :{ "_serverSession" :{ "handle" :{}}, "_isExplicit" : false }},
"_name" : "test" , "_session" :{}},
"_collName" : "sums" , "_cursorHandle" :{}
}
This shows the final sums as
9223372036854 866000 ,
9223372036854 864000 , and
9223372036854 820100 .111111111111111.
The real sum of these numbers is 9223372036854 775807 + 44249 = 9223372036854 820056 , and adding the numbers in each of the documents respectively, the sums should be:
9223372036854 865159 ,
9223372036854 862836 , and
9223372036854 820156 .111111111111111 respectively.
It appears to be rounding to (not necessarily the nearest) thousand, and, in the final case where $num is a NumberDecimal, simply adding the value of $num afterwards.
When the test is run with SBE disabled, the output is:
{ "_batch" :[
{ "_id" :102, "test" :{ "$numberDecimal" : "9223372036854820964.111111111111111" }},
{ "_id" :101, "test" :9223372036854864000},
{ "_id" :100, "test" :9223372036854866000}
],
"_cursorid" :{ "$numberLong" : "0" }, "_ns" : "test.sums" , "_db" :{ "_mongo" :{ "slaveOk" : false , "host" : "localhost:20000" , "defaultDB" : "test" , "_defaultSession" :{ "_serverSession" :{ "handle" :{}}, "_isExplicit" : false }}, "_name" : "test" , "_session" :{}}, "_collName" : "sums" , "_cursorHandle" :{}
}
In this case, the sums for documents 100 and 101 are the same, but the sum for document 102 is:
9223372036854 820964 .111111111111111
which is exactly 864 higher than what the other engine had. In fact, whenever $num is a NumberDecimal, the outcomes with SBE enabled or disabled have a difference of exactly 864.
Bug
Major - P3