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POWhy does SQLite take such a long time to fetch the data?
 

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  1. POWhy does SQLite take such a long time to fetch the data?
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    <p>I have two possible queries, both giving the result set I want.</p> <p>Query one takes about 30ms, but 150ms to fetch the data from the database.</p> <pre><code>SELECT id FROM featurevalues as featval3 WHERE featval3.feature IN (?,?,?,?) AND EXISTS ( SELECT 1 FROM product_to_value, product_to_value as prod2, features, featurevalues WHERE product_to_value.feature = features.int AND product_to_value.value = featurevalues.id AND features.id = ? AND featurevalues.id IN (?,?) AND product_to_value.product = prod2.product AND prod2.value = featval3.id ) </code></pre> <p>Query two takes about 3ms -this is the one I therefore prefer-, but also takes 170ms to fetch the data.</p> <pre><code>SELECT ( SELECT prod2.value FROM product_to_value, product_to_value as prod2, features, featurevalues WHERE product_to_value.feature = features.int AND product_to_value.value = featurevalues.id AND features.id = ? AND featurevalues.id IN (?,?) AND product_to_value.product = prod2.product AND prod2.value = featval3.id ) as id FROM featurevalues as featval3 WHERE featval3.feature IN (?,?,?,?) </code></pre> <p>The 170ms seems to be related to the number of rows from table featval3. After an index is used on featval3.feature IN (?,?,?,?), 151 items "remain" in featval3.</p> <p>Is there something obvious I am missing regarding the slow fetching? As far as I know everything is properly indexed.. I am confused because the second query only takes a blazing 3ms to run.</p> <p><strong>Update</strong></p> <p>This is what i get when I'm running an EXPLAIN on the second query:</p> <pre><code>0 Trace 0 0 0 00 1 Variable 4 1 4 00 2 Goto 0 88 0 00 3 OpenRead 5 6883 0 00 4 If 6 16 0 00 5 Integer 1 6 0 00 6 OpenEphemeral 7 1 0 00 7 Null 0 8 0 00 8 MakeRecord 1 1 8 00 9 IdxInsert 7 8 0 00 10 MakeRecord 2 1 8 00 11 IdxInsert 7 8 0 00 12 MakeRecord 3 1 8 00 13 IdxInsert 7 8 0 00 14 MakeRecord 4 1 8 00 15 IdxInsert 7 8 0 00 16 Rewind 7 86 0 00 17 Column 7 0 5 00 18 IsNull 5 85 0 00 19 Affinity 5 1 0 00 20 SeekGe 5 85 5 00 21 IdxGE 5 85 5 01 22 Null 0 10 0 00 23 Integer 1 11 0 00 24 MustBeInt 11 0 0 00 25 IfZero 11 82 0 00 26 Variable 1 12 3 00 27 OpenRead 2 25 0 00 28 OpenRead 8 7005 0 00 29 OpenRead 9 26 0 00 30 OpenRead 10 6732 0 00 31 OpenRead 11 6766 0 00 32 Column 5 1 15 00 33 IsNull 15 77 0 00 34 Affinity 15 1 0 00 35 SeekGe 8 77 15 00 36 IdxGE 8 77 15 01 37 IdxRowid 8 8 0 00 38 Seek 2 8 0 00 39 Column 2 0 16 00 40 IsNull 16 76 0 00 41 Affinity 16 1 0 00 42 SeekGe 9 76 16 00 43 IdxGE 9 76 16 01 44 Column 9 1 17 00 45 IsNull 17 75 0 00 46 SCopy 12 18 0 00 47 IsNull 18 75 0 00 48 Affinity 17 2 0 00 49 SeekGe 10 75 17 00 50 IdxGE 10 75 17 01 51 If 20 59 0 00 52 Integer 1 20 0 00 53 OpenEphemeral 13 1 0 00 54 Null 0 21 0 00 55 MakeRecord 13 1 21 00 56 IdxInsert 13 21 0 00 57 MakeRecord 14 1 21 00 58 IdxInsert 13 21 0 00 59 Rewind 13 74 0 00 60 Column 13 0 19 00 61 IsNull 19 73 0 00 62 Affinity 19 1 0 00 63 SeekGe 11 73 19 00 64 IdxGE 11 73 19 01 65 Column 9 2 21 00 66 Column 11 0 7 00 67 Ne 7 72 21 6a 68 Column 8 0 22 00 69 Move 22 10 1 00 70 AddImm 11 -1 0 00 71 IfZero 11 77 0 00 72 Next 11 64 0 00 73 Next 13 60 0 00 74 Next 10 50 0 00 75 Next 9 43 0 00 76 Next 8 36 0 00 77 Close 2 0 0 00 78 Close 8 0 0 00 79 Close 9 0 0 00 80 Close 10 0 0 00 81 Close 11 0 0 00 82 SCopy 10 9 0 00 83 ResultRow 9 1 0 00 84 Next 5 21 0 00 85 Next 7 17 0 00 86 Close 5 0 0 00 87 Halt 0 0 0 00 88 Transaction 0 0 0 00 89 VerifyCookie 0 319 0 00 90 TableLock 0 14 0 00 91 TableLock 0 25 0 00 92 TableLock 0 11 0 00 93 Goto 0 3 0 00 </code></pre> <p>Not sure what it means however.</p>
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