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POOptimize MongoDB Query or Index
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copied!<p>I am running a quite ordinary MongoDB query, nothing really complex or special and I am wondering if the time it takes (> 1 sec) is normal or if there's something wrong with my indexes.</p> <p>I provided an index for this specific query and <code>explain()</code> also tells me it is used, but it makes a full scan of the collection each time and slows down the whole webpage by > 1 sec.</p> <p>The query:</p> <pre><code>db.tog_artikel.find({"art_filter":{"$exists":false},"$where":"this._id == this.art_hauptartikelnr"}) </code></pre> <p>Explained:</p> <pre><code>> db.tog_artikel.find({"art_filter":{"$exists":false},"$where":"this._id == this.art_hauptartikelnr"}).explain() { "cursor" : "BtreeCursor art_filter_1_art_hauptartikelnr_1", "nscanned" : 21306, "nscannedObjects" : 21306, "n" : 21306, "millis" : 1180, "nYields" : 0, "nChunkSkips" : 0, "isMultiKey" : false, "indexOnly" : false, "indexBounds" : { "art_filter" : [ [ null, null ] ], "art_hauptartikelnr" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ] } } </code></pre> <p>The index:</p> <pre><code>{ "v": 1, "key": { "art_filter": 1, "art_hauptartikelnr": 1 }, "ns": "togshop.tog_artikel", "background": true, "name": "art_filter_1_art_hauptartikelnr_1" } </code></pre> <p>Why is the full collection scanned every time? Why is <code>isMultiKey</code> false and how can I optimize this query/index?</p> <p>Environment is a standalone server, MongoDB 2.0.1, 64-Bit Linux, accessed from PHP w/ php-mongo 1.2.6</p>

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