RE: Fuzzy checkpoints.

My concerns center about whether or not I can reliably recover after writing out a partial page then dying. Previously it seemed to be a very clear cut situation, now it seems fuzzier :) What if your page header is now inaccurate? What occurs if during fast recovery it is discovered that the time stamps for a given page differ? I didn't see anything which addressed this dilemma at the web site, if I missed something please tell me Thanks for the link, Will >===== Original Message From "Bernstein, Rick" <rbernste@alarismed.com> ===== >The information at the following Web site may alleviate your concerns. > >http://members.tripod.com/markscranton/informix/monthly_topic.htm#Fuzzy >Checkpoints > >The Monthly topic for April 2000 describes fuzzy checkpoints in more >detail. > >-----Original Message----- >From: William Rice [mailto:ricew@operamail.com] >Sent: Tuesday, May 02, 2000 11:53 >To: informix list >Subject: Fuzzy checkpoints. > > >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. > >Example: > Begin work; > Insert record; > Commit work; > ... > Cleaner starts writing page to disk; > SA unplugs machine before write completes. > When machine comes back up there is no Physical log of the before > image from the last checkpoint. > DBA has to find most recent backup. > >Considering that many of our machines are continuously doing I/O due >to low LRU_MAX_DIRTY values I would imagine that the probability >of being in the middle of a write when power was lost would not be low >enough for my taste. > >I do make the assumption that 7.x was able to determine that a page had >not been fully written to the physical log. Considering that the last thing >in a page is the current timestamp, this seems to be a reasonable >assumption. > >Am I missing something, or misunderstanding the current implementation? > >Will > >------------------------------------------------------------ >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/ >------------------------------------------------------------