Re: [HACKERS] SetQuerySnapshot, once again
Hiroshi Inoue [EMAIL PROTECTED] writes: Tom Lane wrote: Sorry, I don't understand ... Let t be a table which is defined as create table t (id serial primary key, dt text); Then is the following function *stable* ? create function f1(int4) returns text as ' declare txt text; begin select dt into txt from t where id = $1; return txt; end ' language plpgsql; I'm not sure exactly what you mean by stable here. And I'm even less sure whether you are arguing for or against adding SetQuerySnapshot calls into plpgsql... regards, tom lane ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] SetQuerySnapshot, once again
-Original Message- From: Tom Lane [mailto:[EMAIL PROTECTED]] Hiroshi Inoue [EMAIL PROTECTED] writes: Tom Lane wrote: Sorry, I don't understand ... Let t be a table which is defined as create table t (id serial primary key, dt text); Then is the following function *stable* ? create function f1(int4) returns text as ' declare txt text; begin select dt into txt from t where id = $1; return txt; end ' language plpgsql; I'm not sure exactly what you mean by "stable" here. Wasn't it you who defined *stable* as 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. ? And I'm even less sure whether you are arguing for or against adding SetQuerySnapshot calls into plpgsql... I already mentioned an opinion in 2001/09/08. Both the command counters and the snapshots in a function should advance except the leading SELECT statements. regards, Hiroshi Inoue ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
Re: [HACKERS] SetQuerySnapshot, once again
Hiroshi Inoue [EMAIL PROTECTED] writes: I'm not sure exactly what you mean by stable here. Wasn't it you who defined *stable* as 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. Oh, *that* stable ;-) Okay, I get your point now. You are right --- a function that references a table that others might be concurrently changing would not be stable under read-committed rules. (But you could probably get away with marking it stable anyway.) I already mentioned an opinion in 2001/09/08. Both the command counters and the snapshots in a function should advance except the leading SELECT statements. I do not like the idea of treating the first select in a function differently from the rest. And such a rule wouldn't let you build guaranteed-stable functions anyway; what if the outer query was calling both your function, and another one that did cause the snapshot to advance? The behavior of your function would then vary depending on whether the other function was invoked or not. regards, tom lane ---(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
Re: [HACKERS] SetQuerySnapshot, once again
Tom Lane wrote: "Hiroshi Inoue" [EMAIL PROTECTED] writes: I already mentioned an opinion in 2001/09/08. Both the command counters and the snapshots in a function should advance except the leading SELECT statements. I do not like the idea of treating the first select in a function differently from the rest. And such a rule wouldn't let you build guaranteed-stable functions anyway; AFAIK there has been no analysis where we can get *stable* functions. As far as I see, we can expect SELECT-only functions to be *stable* if and only if they are surrounded by SELECT-only *stable* functions. regards, Hiroshi Inoue http://w2422.nsk.ne.jp/~inoue/ ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
