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When a very large number of documents matches the query the count of deleted documents can overflow and become negative. I have reproduced this with 3.2.10. It works correctly in 3.4.6. This ticket might be a duplicate, but I couldn't find a ticket for this.
charlie.swanson commented on Fri, 21 Jul 2017 16:08:06 +0000: I'm actually going to re-open this. While attempting to find which version this was fixed in, I realized there are actually many types involved in tracking how many deletes occurred on master, including: On mongod: local variable n in serializeReply, which uses a 'long long'. SingleWriteResult (generated by the IDL file), which uses a 'long', which it looks like IDL translates to an int64_t. The information on the SingleWriteResult looks to be filled out by requesting the number of deleted things from the DeleteStage, which does so by consulting it's DeleteStats, which uses a size_t On mongos: BatchWriteOp, which uses a 'int' BatchCommandResponse, which uses a 'long long' So it looks like all the types on mongod are ok (though the size_t should probably be replaced with a uint64_t, just to be sure). However, this is probably still a problem on mongos, and may still be a problem for update (or insert?). rstam if you're concerned with just a single mongod, it looks like this was likely fixed by SERVER-23128, which deleted the offending WriteOpStats which was storing an int. rstam commented on Fri, 21 Jul 2017 14:38:44 +0000: It would be helpful to users to know exactly which version this was fixed in. ian@10gen.com commented on Fri, 21 Jul 2017 14:35:33 +0000: Since this is already fixed in 3.4 and is simply a reporting error, we have no plans to fix this in 3.2.
Create a collection named "test" with 2,147,483,648 documents. That's one more than the largest possible positive number that can be represented with a 32 bit signed integer. Run the following command: db.runCommand({ delete : "test", deletes : [ { q : {}, limit : 0 } ] }) The expected result is: { "ok" : 1, "n" : 2147483648 } The actual result is: { "ok" : 1, "n" : -2147483648 }
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