Doctrine DBAL
  1. Doctrine DBAL
  2. DBAL-93

[ORACLE] Speed improvement of mechanism for limiting query results

    Details

    • Type: Improvement Improvement
    • Status: Resolved
    • Priority: Minor Minor
    • Resolution: Fixed
    • Affects Version/s: 2.0.1
    • Fix Version/s: 2.1
    • Component/s: Platforms
    • Labels:
      None
    • Environment:
      any

      Description

      Currently the mechanism for limiting query results in Oracle is suboptimal.

      Doctrine uses the following pseudo SQL statement to limit query results:

      SELECT b.* FROM (
         SELECT a.*, ROWNUM AS doctrine_rownum FROM (
            $query
        ) a
      ) b
      WHERE doctrine_rownum BETWEEN $min AND $max
      

      It's much faster to use the following:

      SELECT * FROM (
        SELECT a.*, rownum AS doctrine_rownum FROM {
          $query
        ) a WHERE rownum <= $max
      ) WHERE doctrine_rownum >= $min
      

      The updated code in DBAL/Platforms/OraclePlatform.php would look like this:

      public function modifyLimitQuery($query, $limit, $offset = null)
      {
      	$limit = (int) $limit;
      	$offset = (int) $offset;
      	if (preg_match('/^\s*SELECT/i', $query)) {
      		if ( ! preg_match('/\sFROM\s/i', $query)) {
      			$query .= " FROM dual";
      		}
      		if ($limit > 0) {
      			$max = $offset + $limit;
      			$column = '*';
      			if ($offset > 0) {
      				$min = $offset + 1;
      				$query = 'SELECT * FROM (SELECT a.' . $column . ', rownum AS doctrine_rownum FROM (' . 
      						 $query . 
      						 ') a WHERE rownum <= ' . $max . ') WHERE doctrine_rownum >= ' . $min;
      			} else {
      				$query = 'SELECT a.'.$column.' FROM (' . $query .') a WHERE ROWNUM <= ' . $max;
      			}
      		}
      	}
      	return $query;
      }
      

      With the current implementation the request for fairly complicated query selecting data from multiple tables one of which reaches 2 million rows takes 5.98 seconds comparing to 1.64 with the proposed one.

      In addition It would be nice to have the min and max values as SQL query parameters so that Oracle's internal caching mechanisms could take part, but I'm aware of the fact that it would not be so easy to implement.

        Activity

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        Benjamin Eberlei added a comment -

        Fixed

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        Benjamin Eberlei added a comment - Fixed

          People

          • Assignee:
            Benjamin Eberlei
            Reporter:
            Martin Ivičič
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            Dates

            • Created:
              Updated:
              Resolved: