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POVery slow performance in getting the results of QSqlQuery
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  1. POVery slow performance in getting the results of QSqlQuery
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    copied!<p>I am seeing inexplicably slow behavior from a sqlite database in Qt. The query in the code below, when executed from the sqlite command line utility on the same database, completes instantaneously.</p> <pre><code>qDebug() &lt;&lt; "Beginning" &lt;&lt; QDateTime::currentDateTime ().toString(Qt::ISODate); QSqlQuery q(QSqlDatabase::database(mFilename)); q.prepare( "select TextFormIndex.Id from TextFormIndex,MorphologicalAnalysisMembers,Allomorph on TextFormId=Id and AllomorphId=Allomorph._id where LexicalEntryId=:Id;" ); q.bindValue(":Id", id); QSet&lt;qlonglong&gt; textFormIds; if( !q.exec() ) { qWarning() &lt;&lt; "DatabaseAdapter::lexicalEntryTextForms" &lt;&lt; q.lastError().text() &lt;&lt; q.executedQuery(); return textFormIds; } qDebug() &lt;&lt; "Before while" &lt;&lt; QDateTime::currentDateTime ().toString(Qt::ISODate); int nResults = 0; while( q.next() ) { qDebug() &lt;&lt; nResults++ &lt;&lt; QDateTime::currentDateTime().toString(Qt::ISODate); q.value(0).toLongLong(); } qDebug() &lt;&lt; "After while"; </code></pre> <p>The debug output form this code is:</p> <pre><code>Beginning "2013-02-04T20:31:24" Before while "2013-02-04T20:31:26" 0 "2013-02-04T20:31:26" 1 "2013-02-04T20:31:27" 2 "2013-02-04T20:31:41" 3 "2013-02-04T20:31:44" After while </code></pre> <p>Somehow the third call is taking fourteen seconds.</p> <p>This is a single method in a good-sized project. None of my queries have been executing slowly until this one.</p> <pre><code>create table if not exists TextFormIndex ( TextName text, LineNumber integer, Id integer ); create table if not exists MorphologicalAnalysisMembers ( _id integer primary key autoincrement, TextFormId integer, AllomorphId integer, AllomorphOrder integer ); create table if not exists Allomorph ( _id integer primary key autoincrement, LexicalEntryId integer, WritingSystem integer, Form text ); </code></pre> <p>MorphologicalAnalysisMembers.AllomorphId corresponds to Allomorph._id. TextFormIndex.Id corresponds to MorphologicalAnalysisMembers.TextFormId.</p> <p>MorphologicalAnalysisMembers has 4082 rows TextFormIndex has 17710 rows Allomorph has 1660 rows</p>
 

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