Tom Lane writes: > Since I'm about to have to edit pg_proc.h to add a namespace column, > I thought this would be a good time to revise the current proiscachable > column into the three-way cachability distinction we've discussed > before. But I need some names for the values, and I'm not satisfied > with the ideas I've had so far.
Well, for one thing, we might want to change the name to the correct spelling "cacheable". > 1. Strictly cachable (a/k/a constant-foldable): given fixed input > values, the same result value will always be produced, for ever and > ever, amen. Examples: addition operator, sin(x). Given a call > of such a function with all-constant input values, the system is > entitled to fold the function call to a constant on sight. deterministic (That's how SQL99 calls it.) > 2. Cachable within a single command: given fixed input values, the > result will not change if the function were to be repeatedly evaluated > within a single SQL command; but the result could change over time. > Examples: now(); datetime-related operations that depend on the current > timezone (or other SET-able variables); any function that looks in > database tables to determine its result. "cacheable" seems OK for this. > 3. Totally non-cachable: result may change from one call to the next, > even within a single SQL command. Examples: nextval(), random(), > timeofday(). (Yes, timeofday() and now() are in different categories. > See >http://www.ca.postgresql.org/users-lounge/docs/7.2/postgres/functions-datetime.html#FUNCTIONS-DATETIME-CURRENT) not deterministic, not cacheable -- Peter Eisentraut [EMAIL PROTECTED] ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
