Re: Un-attended Large Archives (fwd)

Chad Larson writes: |> And, of course, this is what we do. We set the BLOCKSIZE to smaller |> than the buffer size on a pipe, and then set the TAPESIZE parameter to |> an effective infinity. We arrange for the program sucking on the pipe |> to buffer during tape changes. Informix never sees an end-of-media |> indication. |> |> In fact, the whole purpose of this subtrafuge is to keep Informix from |> seeing end-of-media, to avoid the global lock imposed during the media |> change period. I'm afraid this last statement is incorrect. There is no "global lock imposed" during the tape switch. What happens is that a checkpoint cannot complete until it co-ordinates with the archive process (we need physlog images to be able to perform archives while the system is on-line, so the physlog cannot be "emptied" until the checkpoint knows that archibe got all the pages it needed). Since waiting for a new tape holds up the archive, the archive then holds up the checkpoint, and everyone else waits for the checkpoint. In this situation, your system can be "frozen" until the tape is changed so the archive can continue and get the physlog pages which allows the checkpoint to complete which allows users to continue (whew!). You imply that, by design, the system is intentionally locked during media changes and this is incorrect. In fact, this problem can generally be avoided by choosing a checkpoint frequency longer than the default 5 minutes (there is little reason to have such frequent checkpoints, in my opinion), better yet, choosing a checkpoint interval greater than the amount of time it would take to change the tape. While a "freeze" is still possible (should your checkpoint happen to fall while a tape is being changed anyway), it becomes less likely than with frequent checkpoints. I usually suggest letting the size of your physical log determine checkpoint frequency (i.e. set CKPTINTVL to a large number). Dave Disclaimer: These opinions are not those of Informix Software, Inc. ************************************************************************** "I look back with some satisfaction on what an idiot I was when I was 25, but when I do that, I'm assuming I'm no longer an idiot." - Andy Rooney