Michael Paesold wrote: > Tom Lane <[EMAIL PROTECTED]> wrote: > > > "Zeugswetter Andreas SB SD" <[EMAIL PROTECTED]> writes: > > > Note also, that a typical SELECT only session would not advance > > > CURRENT_TIMESTAMP at all in the typical "autocommit off" mode that > > > the Spec is all about. > > > > True, but the spec also says to default to serializable transaction > > mode. So in a single-transaction session like you are picturing, > > the successive SELECTs would all see a frozen snapshot of the database. > > Freezing CURRENT_TIMESTAMP goes right along with that, and in fact makes > > a lot of sense, because it tells you exactly what time your snapshot > > of the database state was taken. > > > > This line of thought opens another can of worms: should the behavior > > of CURRENT_TIMESTAMP depend on serializable vs. read-committed mode? > > Maybe SetQuerySnapshot is the routine that ought to capture the > > "statement-start-time" timestamp value. We could define > > CURRENT_TIMESTAMP as the time of the active database snapshot. > > Or at least offer a fourth parameter to that parameterized now() to > > return this time. > > > > regards, tom lane > > That is a very good point. At least with serializable transactions it seems > perfectly reasonable to return a frozen CURRENT_TIMESTAMP. What do you think > about read-commited level? Can time be commited? ;-) > It would be even more surprising to new users if the implementation of > CURRENT_TIMESTAMP would depend on trx serialization level.
Yes, CURRENT_TIMESTAMP changing based on transaction serializable/read commited would be quite confusing. Also, because our default is read committed, we would end up with CURRENT_TIMESTAMP being statement level, which actually does give us a logical place to allow CURRENT_TIMESTAMP to change, but I thought people voted against that. However, imagine a query that used CURRENT_TIMESTAMP in the WHERE clause to find items that were not in the future. Would a CURRENT_TIMESTAMP test in a multi-statement transaction want to check based on transaction start, or on the tuples visible at the time the statement started? -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(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
