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POMongoDB sorts incorrectly when using an index
 

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  1. POMongoDB sorts incorrectly when using an index
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    <p>Here is the query:</p> <pre><code>db.posts.find({"project.id":5,"project.sections":6,"reading":0,"publicate":1},{"date":1}).sort({"date":-1}).limit(20) </code></pre> <p>And here is the output for it:</p> <pre><code>{ "_id" : ObjectId("51342351b6f8f38564000001"), "date" : ISODate("2013-03-05T12:38:41.731Z") } { "_id" : ObjectId("510ff98da80f733357000002"), "date" : ISODate("2013-02-04T19:20:25.618Z") } { "_id" : ObjectId("50fe4bafb6f8f3a14d000002"), "date" : ISODate("2013-01-22T08:45:16.590Z") } { "_id" : ObjectId("50fada8ea80f737202000039"), "date" : ISODate("2013-01-19T19:16:23.294Z") } { "_id" : ObjectId("50e0101fa80f73d664000002"), "date" : ISODate("2012-12-30T09:58:33.881Z") } { "_id" : ObjectId("50dd54d4b6f8f3923d000014"), "date" : ISODate("2012-12-30T09:52:30.993Z") } { "_id" : ObjectId("50ccd4a0a80f73b742000008"), "date" : ISODate("2012-12-15T20:58:18.946Z") } { "_id" : ObjectId("50c0e38eb6f8f32121000018"), "date" : ISODate("2012-12-06T18:35:43.098Z") } { "_id" : ObjectId("50314562b6f8f3f844000000"), "date" : ISODate("2012-08-22T07:06:54.822Z") } { "_id" : ObjectId("502012f3b6f8f3df3a000001"), "date" : ISODate("2012-08-06T19:23:10.586Z") } { "_id" : ObjectId("4fe6ea5ab6f8f39f59000000"), "date" : ISODate("2012-06-24T10:25:32.969Z") } { "_id" : ObjectId("516bbcb2a80f73a55a000000"), "date" : ISODate("2013-04-15T10:36:32.688Z") } { "_id" : ObjectId("516a5f62a80f733e60000000"), "date" : ISODate("2013-04-14T09:00:19.459Z") } { "_id" : ObjectId("515e3f2ca80f738536000003"), "date" : ISODate("2013-04-05T03:07:53.960Z") } { "_id" : ObjectId("5155b7c4b6f8f3ad15000001"), "date" : ISODate("2013-03-29T16:18:44.228Z") } { "_id" : ObjectId("514009e8a80f73f429000001"), "date" : ISODate("2013-03-29T12:31:01.898Z") } { "_id" : ObjectId("515566d5a80f73437d000005"), "date" : ISODate("2013-03-29T10:10:15.113Z") } { "_id" : ObjectId("514572cbb6f8f36525000001"), "date" : ISODate("2013-03-17T07:39:33.738Z") } { "_id" : ObjectId("51432a77b6f8f3024d000000"), "date" : ISODate("2013-03-15T14:07:46.648Z") } { "_id" : ObjectId("513d4afcb6f8f3727b000000"), "date" : ISODate("2013-03-11T17:46:21.183Z") } </code></pre> <p>As you can see, the order is wrong as if sorting works in some weird way. Here is the output of explain() for that query:</p> <pre><code>"cursor" : "BtreeCursor project.id_1_project.sections_1_reading_1_publicate_1_date_-1", "nscanned" : 929, "nscannedObjects" : 915, "n" : 8, "millis" : 23, "nYields" : 0, "nChunkSkips" : 0, "isMultiKey" : true, "indexOnly" : false, "indexBounds" : { ...} </code></pre> <p>But if I disable the index it sorts fine:</p> <pre><code>db.posts.find({"project.id":5,"project.sections":3,"reading":0,"publicate":1},{"date":1}).hint({$natural:1}).sort({"date":-1}).limit(20) { "_id" : ObjectId("51475ee4b6f8f3526f000004"), "date" : ISODate("2013-04-16T10:51:04.962Z") } { "_id" : ObjectId("5166e61fa80f73b658000001"), "date" : ISODate("2013-04-11T16:58:11.848Z") } { "_id" : ObjectId("514afc12a80f735162000000"), "date" : ISODate("2013-03-25T02:51:18.309Z") } { "_id" : ObjectId("513db351b6f8f3d601000006"), "date" : ISODate("2013-03-11T10:49:27.585Z") } { "_id" : ObjectId("5105ff74a80f739704000006"), "date" : ISODate("2013-02-19T11:19:57.448Z") } { "_id" : ObjectId("5121de84b6f8f3b20c000009"), "date" : ISODate("2013-02-18T07:58:40.779Z") } { "_id" : ObjectId("511dbc4ab6f8f3a550000006"), "date" : ISODate("2013-02-15T04:51:39.767Z") } { "_id" : ObjectId("51053aafa80f73ae74000002"), "date" : ISODate("2013-01-27T14:44:48.931Z") } { "_id" : ObjectId("50f1c7c4b6f8f3ed2e000003"), "date" : ISODate("2013-01-12T20:48:04.451Z") } { "_id" : ObjectId("50ec5111b6f8f3180e000034"), "date" : ISODate("2013-01-09T10:25:50.736Z") } { "_id" : ObjectId("50d36076b6f8f3707400000f"), "date" : ISODate("2012-12-20T19:14:40.412Z") } { "_id" : ObjectId("50b4f7b6b6f8f3d261000003"), "date" : ISODate("2012-11-27T17:52:24.675Z") } { "_id" : ObjectId("50a0b83eb6f8f30a74000001"), "date" : ISODate("2012-11-12T09:14:04.652Z") } { "_id" : ObjectId("5092746eb6f8f3c92d000000"), "date" : ISODate("2012-11-06T12:02:21.634Z") } { "_id" : ObjectId("50926d48b6f8f31d15000000"), "date" : ISODate("2012-11-01T13:11:40.107Z") } { "_id" : ObjectId("508a471cb6f8f33568000000"), "date" : ISODate("2012-10-26T19:41:50.516Z") } { "_id" : ObjectId("508998c5b6f8f3b977000000"), "date" : ISODate("2012-10-26T07:59:18.278Z") } { "_id" : ObjectId("5088c043b6f8f3442b000003"), "date" : ISODate("2012-10-25T05:08:12.372Z") } { "_id" : ObjectId("50857833b6f8f37770000001"), "date" : ISODate("2012-10-22T17:06:37.667Z") } { "_id" : ObjectId("507e2f0ab6f8f34c2d000000"), "date" : ISODate("2012-10-17T04:32:10.337Z") } </code></pre> <p>I have tried rebuilding the index for the whole collection using db.bla.reIndex(), it didn't help. All other queries on the same collection that use the same index work just fine.</p> <p>MongoDB 2.0.9</p> <p>What could be the reason behind this behaviour?</p>
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    1. USrakhim
    1. USrakhim
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      1. POMongoDB sorts incorrectly when using an index
      1. USAdam Comerford
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    1. COYour query has a limit of 10 documents, but your result you're showing contains more than 10 documents. Is the output really the content of your query?
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      1. USphilnate
    2. COSorry, my bad, just changed the limit and mixed up the lines. It is the correct output though, double checked.
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      1. USrakhim
    3. COOut of interest, what is the index you made? What fields was it on?
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      1. USSammaye
 

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