Re: Discussion: Is a server with truncated logs safe?

On 05/05/11 12:08, Jarrod Teale wrote: > So today we had the mother of all nasty scenarios. > > The server crashed and when restarting said “Cannot roll forward from > checkpoint, contact IBM support”. > > Logical logs were in a mess. Not good. So IBM dial in and truncate the > logs and sort the system out so it starts – yeah for onlog J > > They recommend not using the database anymore, but unloading everything > and moving it to a new instance to ensure consistency. > > > > I buy the argument completely and it is the right thing to do. > > > > But... The issue I have is this – we can’t really afford the downtime > until the milk season winds down for winter in a month or two. > > So... my question. > > What is the consensus about running on a database that has been log > truncated? > > > > I want opinion on how urgent the full server rebuild is. > > If we have to do it today, then we need to try to find a way to do it > with as little downtime as possible because the plant will still be > running. This will be VERY complicated and basically the definition of > annoying. > > > > On your marks, get set, discuss... > > > > Thanks > > > > Jarrod Teale > The answer is 'how long is a piece of string'? It very much depends on the extent of the corruption. Advanced support has tools to selectively truncate recovery on specific tables or even records (I know, because I have written them): in this particular circumstance you would be able to get away with just fixing the tables involved. But if the corruption was too widespread for surgical intervention, the amount of potential corruption after recovery truncation could be enormous. To top it off, the corruption could be apparent (corrupted indexes, data pages, blobs) prompting you to rebuild the instance, on the grounds that it's just unusable, or it might be not (as in, the data might be incorrect from a business point of view, but correct as far as storage goes), and you'll find yourself in the uncomfortable position of taking wrong business decisions based on wrong data. -- Ciao, Marco ______________________________________________________________________________ Marco Greco /UK /IBM Standard disclaimers apply! Structured Query Scripting Language http://www.4glworks.com/sqsl.htm 4glworks http://www.4glworks.com Informix on Linux http://www.4glworks.com/ifmxlinux.htm