Core

DataHandler->fillInFieldArray calls

$eFile = \TYPO3\CMS\Core\Html\RteHtmlParser::evalWriteFile($vconf['spec']['static_write'], array_merge($currentRecord, $fieldArray));

for each field of each record to insert. In each call array_merge($currentRecord, $fieldArray) is done only to throw it away again immediately and do nothing in most cases - does anyone use staticFileEditPath? I dont't think so: http://forum.typo3.org/index.php/t/195196/

$types_fieldConfig = BackendUtility::getTCAtypes($table, $currentRecord);
$theTypeString = BackendUtility::getTCAtypeValue($table, $currentRecord);
if (is_array($types_fieldConfig)) {
    foreach ($types_fieldConfig as $vconf) {
        // Write file configuration:
        // inserted array_merge($currentRecord,$fieldArray) 170502
        $eFile = \TYPO3\CMS\Core\Html\RteHtmlParser::evalWriteFile($vconf['spec']['static_write'], array_merge($currentRecord, $fieldArray));
        // RTE transformations:
        if (!$this->dontProcessTransformations) {
}

Instead of unconditionally merging and throwing away again only merge if static_write is enabled

$types_fieldConfig = BackendUtility::getTCAtypes($table, $currentRecord);
$theTypeString = BackendUtility::getTCAtypeValue($table, $currentRecord);
if (is_array($types_fieldConfig)) {
    foreach ($types_fieldConfig as $vconf) {
        if (is_array($vconf['spec']['static_write']) && $GLOBALS['TYPO3_CONF_VARS']['BE']['staticFileEditPath']) {
            // only do array_merge if static_write is enabled
            $eFile = \TYPO3\CMS\Core\Html\RteHtmlParser::evalWriteFile($vconf['spec']['static_write'], array_merge($currentRecord, $fieldArray));
        } else {
            $eFile = null;
        }
        // RTE transformations:
        if (!$this->dontProcessTransformations) {

I think even more easy optimizations are possible here (keep array_merge and do not create again in $mixedRec = array_merge($currentRecord, $fieldArray);) but this is only executed if static_write is enabled anyway.

For bulk insert of 6500 records:

• 98000 calls less
• 0.5 seconds faster
• memory usage of array_merge()-Function down from 128MB to 6MB