PHP memory limit reached after converting pwiki_log_visit to InnoDB

Hi,

we have converted the Table pwiki_log_visit from MyISAM to InnoDB. After that, we got a PHP Fatal Error for the reporting view. (over 4 Months Timeframe or more) I´ve increased the PHP Memory Limit to 768MB. But we still get this Errors.

PHP Fatal error: Allowed memory size of 805306368 bytes exhausted (tried to allocate 33554432 bytes) in $DOCROOT/core/DataTable.php on line 1362``

The Size of the Table is: 2088.47 MB and i ran optimize Table after converting. The InnoDB Buffer Pool has a size of 4GB.

Size of some Tables.

| piwik_archive_blob_2016_01 | 248.22 |
| piwik_archive_blob_2016_03 | 250.25 |
| piwik_archive_blob_2016_04 | 656.34 |
| piwik_log_conversion | 858.75 |
| piwik_archive_blob_2015_05 | 1906.91 |
| piwik_log_visit | 2088.47 |
| piwik_log_link_visit_action | 4366.95 |
| piwik_archive_blob_2015_01 | 6337.00 |
±------------------------------±-----------+

The Size of the DB ist: 19076.6 MB

We´ve enabled the Archive Cron.

/usr/bin/php $DOCROOT/console core:archive --url=$URL >> $LOGFIL_date +\%Y-\%m-\%d.log 2>&1

It is an Apache 2.4.20, PHP 5.6 and MySQL 5.6. All on the same Server. Is there any reason, why we got the PHP Error Memory Error, after converting the table.

Kind Regards

Tim