Thanks to Daniel Verite, nice answer, really helpful :)
It summarizes what I have read in the doc and blogs.
What about updates where the bytea do not changed. Does a new copy of the bytea will be made in the toast table or new row will point to the original bytea?
> https://www.postgresql.org/docs/current/storage-toast.html says
> The TOAST management code is triggered only when a row value to be stored in a table is wider than TOAST_TUPLE_THRESHOLD bytes (normally 2 kB). The TOAST code will compress
> and/or move field values out-of-line until the row value is shorter than TOAST_TUPLE_TARGET bytes (also normally 2 kB, adjustable) or no more gains can be had. During an UPDATE
> operation, values of unchanged fields are normally preserved as-is; so an UPDATE of a row with out-of-line values incurs no TOAST costs if none of the out-of-line values change.
Does it means, no incurs cost to generate the out of line toast, but that a copy of the bytea is still made for the new line?
It summarizes what I have read in the doc and blogs.
What about updates where the bytea do not changed. Does a new copy of the bytea will be made in the toast table or new row will point to the original bytea?
> https://www.postgresql.org/docs/current/storage-toast.html says
> The TOAST management code is triggered only when a row value to be stored in a table is wider than TOAST_TUPLE_THRESHOLD bytes (normally 2 kB). The TOAST code will compress
> and/or move field values out-of-line until the row value is shorter than TOAST_TUPLE_TARGET bytes (also normally 2 kB, adjustable) or no more gains can be had. During an UPDATE
> operation, values of unchanged fields are normally preserved as-is; so an UPDATE of a row with out-of-line values incurs no TOAST costs if none of the out-of-line values change.
Does it means, no incurs cost to generate the out of line toast, but that a copy of the bytea is still made for the new line?
Jean-Marc Lessard
Administrateur de base de données / Database Administrator
Ultra Electronics Forensic Technology Inc.
T +1 514 489 4247 x4164
www.ultra-forensictechnology.com
