With the setting -c [size] you can configure how large an initial memory cache you want the database server to allocate. As a standard, if you do not use this setting, the database server will allocate 2 MB internal (primary) memory (RAM).
The best option is to reserve RAM memory corresponding to the entire size of the databases that the database server is running. For example, if the total size that the database runs is 3 GB, then you enter -c 3g (keep in mind that the total database size usually expands as more and more data is saved).
The higher the cache, the better the performance. However, make sure that you do not enter a larger cache size than the available RAM memory since this will have the opposite effect on the performance. Therefore it is wise to equip the computer with a large RAM memory.