mongodb graphLookup 在分片集合中不起作用

Question

我的 testcol 集合如下所示：

mongos> db.testcol.find().limit(3)
{ "_id" : ObjectId("60b871854bea7a9df54f0594"), "ID" : "B1", "CID" : "B2", "DOC" : "Some info" }
{ "_id" : ObjectId("60b8718e4bea7a9df54f0595"), "ID" : "B3", "CID" : "B5", "DOC" : "Some info" }
{ "_id" : ObjectId("60b871994bea7a9df54f0596"), "ID" : "B5", "CID" : "B2", "DOC" : "Some info" }
mongos>

在对 testcol 进行分片后，我意识到 $graphLookup 不再工作了：

mongos> db.testcol.aggregate([ { $graphLookup: { from: "testcol", startWith: "B1" , 
connectFromField: "ID", connectToField: "CID", as: "children" } } ])
2021-06-03T07:35:13.242+0200 E QUERY    [js] Error: command failed: {
    "ok" : 0,
    "errmsg" : "test.testcol cannot be sharded",
    "code" : 28769,
    "codeName" : "Location28769",
    "operationTime" : Timestamp(1622698513, 28),
    "$clusterTime" : {
            "clusterTime" : Timestamp(1622698513, 28),
            "signature" : {
                    "hash" : BinData(0,"RObEDuuK9uibPFj/MAoDwSyR3Lc="),
                    "keyId" : NumberLong("6939965305435193347")
            }
    }
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:18:14
_assertCommandWorked@src/mongo/shell/assert.js:580:17
assert.commandWorked@src/mongo/shell/assert.js:673:16
DB.prototype._runAggregate@src/mongo/shell/db.js:260:9
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1062:12
@(shell):1:1
mongos>

根据 mongo docs $graphLookup 不接受来自分片集合，但是 我的集合变得非常大（已经 6TB），似乎我无法保持它不分片，关于如何在分片集合中获取我的图形关系的任何建议？

Answer 1

来自 MongoDB 3.4 以来的文档 (source)：

The collection can be sharded.
The fromCollection cannot be sharded.

编辑 (source2)：

support for sharded "from" collections in $lookup and $graphLookup will be part of the upcoming 5.1 release.