private function _maybeMergeSegments()
    {
        if (Zend_Search_Lucene_LockManager::obtainOptimizationLock($this->_directory) === false) {
            return;
        }

        if (!$this->_hasAnythingToMerge()) {
            Zend_Search_Lucene_LockManager::releaseOptimizationLock($this->_directory);
            return;
        }

        // Update segments list to be sure all segments are not merged yet by another process
        //
        // Segment merging functionality is concentrated in this class and surrounded
        // by optimization lock obtaining/releasing.
        // _updateSegments() refreshes segments list from the latest index generation.
        // So only new segments can be added to the index while we are merging some already existing
        // segments.
        // Newly added segments will be also included into the index by the _updateSegments() call
        // either by another process or by the current process with the commit() call at the end of _mergeSegments() method.
        // That's guaranteed by the serialisation of _updateSegments() execution using exclusive locks.
        $this->_updateSegments();

        // Perform standard auto-optimization procedure
        $segmentSizes = array();
        foreach ($this->_segmentInfos as $segName => $segmentInfo) {
            $segmentSizes[$segName] = $segmentInfo->count();
        }

        $mergePool   = array();
        $poolSize    = 0;
        $sizeToMerge = $this->maxBufferedDocs;
        asort($segmentSizes, SORT_NUMERIC);
        foreach ($segmentSizes as $segName => $size) {
            // Check, if segment comes into a new merging block
            while ($size >= $sizeToMerge) {
                // Merge previous block if it's large enough
                if ($poolSize >= $sizeToMerge) {
                    $this->_mergeSegments($mergePool);
                }
                $mergePool   = array();
                $poolSize    = 0;

                $sizeToMerge *= $this->mergeFactor;

                if ($sizeToMerge > $this->maxMergeDocs) {
                    Zend_Search_Lucene_LockManager::releaseOptimizationLock($this->_directory);
                    return;
                }
            }

            $mergePool[] = $this->_segmentInfos[$segName];
            $poolSize += $size;
        }

        if ($poolSize >= $sizeToMerge) {
            $this->_mergeSegments($mergePool);
        }

        Zend_Search_Lucene_LockManager::releaseOptimizationLock($this->_directory);
    }