Re: tbzero, logs, high water marks

In article <2net3r$s4l@emory.mathcs.emory.edu>, cwa@leia (cwakins@rmc.com) says: > >> TBZERO is the only way I know of. >> >> A released, supported tbzero would be very nice. We've needed >> similar from time to time. There really isn't any other way after >> Informix won't come up. >> >> Jim Burks jburks@promus.com >> Database Administrator >> The Promus Companies > >Watch out for that tbzero. johnl wrote a pretty scathing rebuke of the use >of that program. It is truly a tool of last resort, and its use may be worse >than having to restore from an archive. There is no way to guarantee the >state of your data after a tbzero (or something like that.) > >We used to have that problem, but we learned two things: > > re-write deletes/purges to commit every row > > if the logs get filled up, manaully run the auto-backup from > tbmonitor to free them. This works when the tbtape dies, and the > logs fill from regular use (maybe not from a single huge event). > >This saved us a bunch of hassle that we didn't used to know how to deal with. > >Also, there are several things to keep in mind when sizing logs. Logs take up >memory, and that's expensive. It is possible to have more logs than you need, >adversely affecting other processes thru memory shortage. Your high water >marks are important, (in online >= v.5.0) and a topic of controversy. The >default settings are too high (IMHO). You need enough log space to handle >your largest transaction, plus a fudge factor, plus a rollback. This means >the high water mark should be <50%. This is kind of expensive, though, since >it will abort a transaction that might have only needed 51%. These are >some of the tradeoffs, there are others. > >A pretty good discussion is in the Informix OnLine Administrator's Guide, >version 5.0 December 1991 from page 3-11. > >Good luck, > > __________________________________________________________________ > | Clem Akins Standard Disclaimers Apply | > | Reynolds Metals Co. "Climb High, Cave Deep!" | > | Alloys Plant (MS #59) | > | 3509 East 2nd St Internet: cwa@leia.rmc.com | > | Muscle Shoals, Al Telephone: (205) 386-6783 | > | USA 35661-1256 Facsimile: (205) 386-6831 | > |________________________________________________________________|