Re: Table full message when data is just over 16MB

[Rick James]

Sounds like the product of average row length and maximum rows was under 16MB (2**24). Fix it by changing either or both of those via ALTER TABLE.

Behind the scenes:
MyISAM uses a pointer from indexes into the data. The pointer is either a row offset (if "Fixed"), or a byte offset (if "Dynamic"). See SHOW TABLE STATUS for which it is. The pointers are some number of bytes. Yours seem to be 3 bytes. The old default was 4; the current default is 6. (The default is used when average row length and maximum rows are not specified.)

The pointer size effectively limits the size of a MyISAM table. On the other hand, if the pointer is bigger than needed, the .MYI file is bigger than needed.

Bottom line: The default is fine for 99.9% of cases. If you set average row length or maximum rows, be sure make them at least as big as the table will ever be. Otherwise, you could be stuck with doing a lengthy ALTER.