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Hi Paul, i remember reading on the forum about saving just the last value instead of historic feed data. Memory fits that purpose and gives past data since reboot. It's really up to the user to choose if it fits his need.

Data is kept in ram, so its 'low-write'.

The mysql default limit is 16MB per table, thats about 500.000 data points.

From mysql docs https://dev.mysql.com/doc/refman/5.0/en/memory-storage-engine.html :

MEMORY table contents are stored in memory, which is a property that MEMORY tables share with internal temporary tables that the server creates on the fly while processing queries. However, the two types of tables differ in that MEMORY tables are not subject to storage conversion, whereas internal temporary tables are:

MEMORY tables are never converted to disk tables. If an internal temporary table becomes too large, the server automatically converts it to on-disk storage, as described in Section 8.4.4, “How MySQL Uses Internal Temporary Tables”.

The maximum size of MEMORY tables is limited by the max_heap_table_size system variable, which has a default value of 16MB. To have larger (or smaller) MEMORY tables, you must change the value of this variable. The value in effect for CREATE TABLE is the value used for the life of the table. (If you use ALTER TABLE or TRUNCATE TABLE, the value in effect at that time becomes the new maximum size for the table. A server restart also sets the maximum size of existing MEMORY tables to the global max_heap_table_size value.) You can set the size for individual tables as described later in this section.

Yes, I had read the MySQL docs earlier, but can you give a practical example where this could be used effectively in the emoncms environment?

Paul