Mongodb Java driver: kill running aggegation

user_2221647 0
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I'm atrying to kill an aggregation operation on a sharded cluster programatically. The operation is launched from Java mongo driver,

The way I've found to kill it is throw a killSessions command with the session identifier.

What I do to properly get the sessions identifier is:

MongoClient mongoClient = ....
mongoClient.startSession()

//call the aggregation stuff..

This thread keeps running, and from another thread, I use the mongoClient object to get the server session and kill it:

BsonDocument serverSession = clientSession.getServerSession().getIdentifier();
BsonBinary value = serverSession.get("id").asBinary();

Then I wrap valueinside a singleton collection of document [{ id: value}] and call $killsessions with this parameter. I run it on top of the mongo admin db.

The result returns me { ok: 1.0 }, but the thread with the operation still keeps running and ends properly on the server The result of the aggregation is written to a new collection on stage $out, so it seems it has no effect on the server session.

How can I kill, programatically, all the operations running on the aggregation? (both client & server side).

mongodb java
3 Answers

Once you start a pipeline it is running on your Mongo's process. sessions are a way to guarantee consistency with read/write operations. not a way to kill running queries.

You want to use killOp, get the operation id using currentOp.

user_107703700

Since I needed it to kill long running processes, my solution was to use the following command to univocally identify the session to kill

db.adminCommand({"currentOp": true, "secs_running": {$gte: 100}})

get the id from the result (asumming inprog contains only 1 operation in progress because there's no more operation running for more than 100 seconds,

{ "inprog": [{ "lsid": {here_is_the_session_id}, otherFields...}, otherInProgOps...], otherFields....}

and then pass the lsid field (which contains id and uid) to killSessions:

b.adminCommand( { killSessions: [ {here_goes_lsid} ] } )

For a more confident method to get the sessionId other fields of the inprogarray can be checked

user_22216470

killSessions works in my testing: regular find, aggregation.

Ensure you are killing the session that is used in the operation, ensure the operation is running when you kill the session (you can kill the session prior to the operation starting which will be a no-op), ensure you pass the session in properly.

If you still have trouble provide a reproducible code sample.

killSessions does not return anything hence as far as I can tell there's no way to tell if it actually did anything. But the server logs when it kills operations. 4.4 logs:

{"t":{"$date":"2020-06-16T15:55:06.872-04:00"},"s":"I",  "c":"QUERY",    "id":20528,   "ctx":"threa
d60247","msg":"Killing cursor as part of killing session(s)","attr":{"cursorId":7290821057815339751
}}
{"t":{"$date":"2020-06-16T16:01:29.350-04:00"},"s":"I",  "c":"COMMAND",  "id":20706,   "ctx":"thread60247","msg":"Killing op as part of killing session","attr":{"opId":18212677,"lsid":{"id":{"$uuid":"8f5474a5-8001-469b-87d4-692563f2dc0e"},"uid":{"$binary":{"base64":"47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=","subType":"0"}}}}}
user_95409250
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