Are MySQL databases with a MEMORY storage engine persisted to disk?

Question

If MySQL databases with a MEMORY engine are stored in memory, does this mean that their contents are not persisted to disk? Or are they stored on HDD, but fully loaded into RAM on system power up?

Answer 1

Contents are not persisted to disk, they are lost when You shut down server. This is perfect table type for temporary data.

More here: http://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine.html

Answer 2

There is one file one disk that contains database definition but data never goes on disk. Data is lost when server shut down.

http://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine.html

When tables become overly larges you just get errors. However like any other memory usage it can be swapped... and then will use some disk.