As of 4.9 multiple db connections were added so increasing this value to much could have negative effects on Ram usage.  As it could be 5x your value or in some cases from a beta standpoint 20x your value.  Will try to update when more info is available.   Performace tweaks Database cache size Sets the amount of data that the database will hold in memory at once, per database file. A larger value may help improve Emby Server performance. Requires a server restart to take effe