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  1. Core Server
  2. SERVER-38949

Incorrect index bounds for {$ne: ["String"]} query

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    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Critical - P2 Critical - P2
    • 4.0.9, 4.1.9
    • Affects Version/s: None
    • Component/s: Querying
    • Labels:
    • Fully Compatible
    • ALL
    • v4.0, v3.6, v3.4, v3.2
    • Hide

      Saving this file as repro.js:

      (function() { 
  "use strict"; 


  const coll = db.reproducer; 
  coll.drop(); 


  assert.commandWorked(coll.insert([{_id: 0, str: "Avon"}])); 


  assert.eq(1, coll.find({str: {$ne: ["Avon"]}}).itcount()); 
  assert.commandWorked(coll.ensureIndex({str: 1})); 
  assert.eq(1, coll.find({str: {$ne: ["Avon"]}}).itcount()); // FAILS 
})();

      You can reproduce this failure with

      python buildscripts/resmoke.py repro.js
      Show
      Saving this file as repro.js : ( function () {   "use strict" ;   const coll = db.reproducer;   coll.drop();   assert.commandWorked(coll.insert([{_id: 0, str: "Avon" }]));   assert.eq(1, coll.find({str: {$ne: [ "Avon" ]}}).itcount());   assert.commandWorked(coll.ensureIndex({str: 1}));   assert.eq(1, coll.find({str: {$ne: [ "Avon" ]}}).itcount()); // FAILS })(); You can reproduce this failure with python buildscripts/resmoke.py repro.js
    • Query 2019-02-25
    • 24

      For a query like

      {x: {$not: {$in: [["String"]]}}

      a collection scan will return the document 

      {x: "String"}

      because "String" != ["String"] and so "String" is not in the array [["String"]]. However, if you build an index on {x: 1} then the above document is not returned. Using explain, you can see the index bounds are:

      {
   "x" : [
   	"[MinKey, \"String\")",
   	"(\"String\", [ \"String\" ])",
   	"([ \"String\" ], MaxKey]"
   ]
}

      Compare this to what should be the equivalent query

      {x: {$ne: ["String"]}}

      we then get the bounds:

      {
	"x" : [
		"[MinKey, [ \"String\" ])",
		"([ \"String\" ], [ [ \"String\" ] ])",
		"([ [ \"String\" ] ], MaxKey]"
	]
}

      It looks like the index bounds building logic for an $in within a $not.

            Assignee:
            ian.boros@mongodb.com Ian Boros
            Reporter:
            charlie.swanson@mongodb.com Charlie Swanson
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            13 Start watching this issue

              Created:
              Updated:
              Resolved: