Using storage MAIN

Christopher Kings-Lynne <chriskl@familyhealth.com.au> writes:

Quick question about how column storage works. If you set a TEXT field
to be storage MAIN, does this place a limit on the amount of data that
can be stored in the row (eg. 8k?)

No, because it will still be forced out-of-line if that's the only way
to make the row fit. The source code comments may be helpful:

/*----------
* attstorage tells for VARLENA attributes, what the heap access
* methods can do to it if a given tuple doesn't fit into a page.
* Possible values are
* 'p': Value must be stored plain always
* 'e': Value can be stored in "secondary" relation (if relation
* has one, see pg_class.reltoastrelid)
* 'm': Value can be stored compressed inline
* 'x': Value can be stored compressed inline or in "secondary"
* Note that 'm' fields can also be moved out to secondary storage,
* but only as a last resort ('e' and 'x' fields are moved first).
*----------
*/

You could force no-compression, no-out-of-line semantics by setting it
to PLAIN, and then it *would* fail if over 8K.

regards, tom lane