From e52b57b7a9f0303c0c710e60870d0ec265d32541 Mon Sep 17 00:00:00 2001

From: Milian Wolff <mail@milianw.de>

Date: Mon, 1 Dec 2014 14:11:19 +0100

Subject: [PATCH 19/30] Optimize queries: Do not retrieve known key used in the

 condition.

There is no point in doing a select like:

SELECT foo, bar FROM table WHERE foo = needle;

That can be rewritten to say

SELECT bar FROM table WHERE foo = needle;

This reduces the data traffic with the mysql server. Additionally, it

work-arounds some issues in Qt SQL, which lead to bad performance:

QSqlResult::value incurs multiple temporary allocations, and string

conversions, even to read a simple integer ID for example. Finally,

by reusing an externally provided QString name e.g., we can leverage

Qt's implicit sharing, instead of duplicating the string in a separate

QString instance, with the contents read from SQL server.

REVIEW: 121310

---

 server/src/storage/entities.xsl | 50 +++++++++++++++++++++++++++++------------

 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/server/src/storage/entities.xsl b/server/src/storage/entities.xsl

index 9471293..c8fb1fd 100644

--- a/server/src/storage/entities.xsl

+++ b/server/src/storage/entities.xsl

@@ -104,6 +104,12 @@ Q_DECLARE_TYPEINFO( Akonadi::Server::<xsl:value-of select="@name"/>, Q_MOVABLE_T

 using namespace Akonadi::Server;

+static QStringList removeEntry(QStringList list, const QString& entry)

+{

+  list.removeOne(entry);

+  return list;

+}

+

 <xsl:for-each select="database/table">

 <xsl:call-template name="table-source"/>

 </xsl:for-each>

@@ -179,7 +185,8 @@ set<xsl:value-of select="$methodName"/>( <xsl:call-template name="argument"/> )

     return <xsl:value-of select="$className"/>();

   QueryBuilder qb( tableName(), QueryBuilder::Select );

-  qb.addColumns( columnNames() );

+  static const QStringList columns = removeEntry(columnNames(), <xsl:value-of select="$key"/>Column());

+  qb.addColumns( columns );

   qb.addValueCondition( <xsl:value-of select="$key"/>Column(), Query::Equals, <xsl:value-of select="$key"/> );

   if ( !qb.exec() ) {

     akDebug() << "Error during selection of record with <xsl:value-of select="$key"/>"

@@ -191,21 +198,36 @@ set<xsl:value-of select="$methodName"/>( <xsl:call-template name="argument"/> )

     return <xsl:value-of select="$className"/>();

   }

+  

+  int valueIndex = 0;

+  <xsl:for-each select="column">

+    const <xsl:value-of select="@type"/> value<xsl:value-of select="position()"/> =

+    <xsl:choose>

+      <xsl:when test="@name=$key">

+        <xsl:value-of select="$key"/>;

+      </xsl:when>

+      <xsl:otherwise>

+        (qb.query().isNull(valueIndex)) ?

+        <xsl:value-of select="@type"/>() :

+        <xsl:choose>

+          <xsl:when test="starts-with(@type,'QString')">

+          Utils::variantToString( qb.query().value( valueIndex ) )

+          </xsl:when>

+          <xsl:when test="starts-with(@type, 'Tristate')">

+          static_cast<Tristate>(qb.query().value( valueIndex ).value<int>())

+          </xsl:when>

+          <xsl:otherwise>

+          qb.query().value( valueIndex ).value<<xsl:value-of select="@type"/>>()

+          </xsl:otherwise>

+        </xsl:choose>

+        ; ++valueIndex;

+      </xsl:otherwise>

+    </xsl:choose>

+  </xsl:for-each>

+

   <xsl:value-of select="$className"/> rv(

   <xsl:for-each select="column">

-    (qb.query().isNull(<xsl:value-of select="position() - 1"/>)) ?

-      <xsl:value-of select="@type"/>() :

-      <xsl:choose>

-        <xsl:when test="starts-with(@type,'QString')">

-      Utils::variantToString( qb.query().value( <xsl:value-of select="position() - 1"/> ) )

-        </xsl:when>

-        <xsl:when test="starts-with(@type, 'Tristate')">

-      static_cast<Tristate>(qb.query().value( <xsl:value-of select="position() - 1"/> ).value<int>())

-        </xsl:when>

-        <xsl:otherwise>

-      qb.query().value( <xsl:value-of select="position() - 1"/> ).value<<xsl:value-of select="@type"/>>()

-        </xsl:otherwise>

-      </xsl:choose>

+    value<xsl:value-of select="position()"/>

     <xsl:if test="position() != last()">,</xsl:if>

   </xsl:for-each>

   );

-- 

2.1.0