Info

If the preceding stages generate output in nondeterministic order and $setWindowFields has a default ‘partitionBy’ and ‘sortBy’ a non-existing field, $setWindowFields could generate inconsistent result every time the same pipeline is executed. Due to the same reason, disabling/enabling query optimization could also cause $setWindowFields producing inconsistent result. For example in BF-20745, consider a pipeline [*$bucket + $setWindowFields]* which will be desugared to the following pipeline: [ $group + $sort ({“_id”: 1})  + $sort + $_internalSetWindowFields ]. The two adjacent $sort stages will be optimized to a single $sort by removing the first $sort. However, if the second $sort sorted a non-existing field, $_internalSetWindowFields would still get a non-deterministic order of input because $group does not order its output. It seems not a legit $setWindowFields bug, but it’s failing in some certain agg-fuzzers, e.g. aggregation_wildcard_fuzzer and aggregation_optimization_fuzzer.

Top User Comments

JIRAUSER1259052 commented on Wed, 6 Oct 2021 18:58:39 +0000: Updating the fixversion since branching activities occurred yesterday. This ticket will be in rc0 when it’s been triggered. For more active release information, please keep an eye on #server-release. Thank you! xgen-internal-githook commented on Wed, 26 May 2021 02:10:28 +0000: Author: {'name': 'samontea', 'email': 'merciers.merciers@gmail.com', 'username': 'samontea'} Message: SERVER-56757 Add query knob to ensure that setWindowFields is in deterministic order for testing framework Branch: v5.0 https://github.com/mongodb/mongo/commit/5929fa77a2393235b541f5c26747907822b5dfdd xgen-internal-githook commented on Tue, 25 May 2021 21:24:46 +0000: Author: {'name': 'samontea', 'email': 'merciers.merciers@gmail.com', 'username': 'samontea'} Message: SERVER-56757 Add query knob to ensure that setWindowFields is in deterministic order for testing framework Branch: master https://github.com/mongodb/mongo/commit/9d31696a31388af10b3351ac6f67ad1765d1d48c samuel.mercier commented on Mon, 24 May 2021 23:52:47 +0000: We're going to implement a setParameter which will allow cause the `sortBy` to desugar to a `$sort` statement with and `, _id: 1` part appended. Then we will enable this setParameter with TIG-3025. julian.edwards commented on Wed, 12 May 2021 16:45:06 +0000: Ignore that merge, my ticket was SERVER-56575. xgen-internal-githook commented on Wed, 12 May 2021 01:22:02 +0000: Author: {'name': 'julianedwards', 'email': 'julian.edwards@mongodb.com'} Message: SERVER-56757: Make jasper resmoke work with windows Branch: master https://github.com/mongodb/mongo/commit/b98b00f9d3d15f229762a9e2491a555fc9a7f93c nicholas.zolnierz commented on Mon, 10 May 2021 15:41:03 +0000: Assigning to Sam as more of an investigating ticket. Our last brainstorm idea was to have the fuzzer append "_id" to the generated sort spec for $setWindowFields, such that the order of documents coming into the stage is reliable since the fuzzer appears to preserve the _id field. One caveat is that we'll need to perform the desugaring in the fuzzer since a compound sortBy is not allowed with several window functions.

Steps to Reproduce