RE: Fuzzy checkpoints.

I did read the chapter :) that is what prompted my concern. I will share my original understanding of the purpose of the physical log. This will shed light on my concerns. I thought the purpose of the physical log was to keep a copy of the before image of a page in case any issues were encountered during the write to disk. The logical log record would not have any information about the other data on the page which is being written. If it is deemed as impossible for a write to fail, then I do not understand the purpose of the physical log in the first place except for items which do not go through the logical logs. If there is a partial page write, then a machine crash why wouldn't that page be irrecoverable? My reasons for why I think it is irrecoverable. 1. The timestamps do not match so something is wrong. 2. We don't know how much was written out, so do not know if it wrote just the timestamp, or got all the way to the last slot entry... With the physical log you have that image written out and can use it to stamp over this partially written page What am I missing? Is there someway to figure out all this info? Thanks for any responses, Will P.S. Maybe this is such a rare situation it is a inconsequential... I do not have a machine to test on. >===== Original Message From Rudy Fernandes <rferdy@americasm01.nt.com> ===== >William Rice wrote: > >> I have concerns about whether or not 9.2 is as robust in bad situations >> as 7.x was. >> >> My concerns center around the fact that fuzzy operations(updates, inserts, >> and deletes) are not physically logged To me, this means if >> I unplug my machine in the middle of a write to disk initiated by a >> fuzzy operation I am now going to a backup and rolling forward logical >> logs. >> > >"Fuzzy checkpoint depends on write-ahead logging for fast recovery to work correctly." >Excerpt from the Admin Guide. > >Even though changes that are a result of fuzzy operations are not logged in the >physical log, they are being logged in the logical log. It is from the logical log >that Informix will retrieve fuzzy changes in case they are needed during a "Fast >recovery" that follows a system crash. > >Conceptually, fuzzy checkpoints change nothing in terms of recoverability except that >"Fast Recovery" will usually take a longer time. > >Read the chapter "Checkpoints and Fast Recovery" in the Admin Guide. There's good >stuff in there on this issue. > >Rudy ------------------------------------------------------------ This e-mail has been sent to you courtesy of OperaMail, as a free service from Opera Software, makers of the award-winning Web Browser, Opera. Visit us at http://www.opera.com/ or our portal at: http://www.myopera.com/ Your free e-mail account is waiting at: http://www.operamail.com/ ------------------------------------------------------------