Re: C-ISAM Corrupted Indexes

Greg Bryan (gbryan@ssf-sys.dhl.com) writes: > More sophisticated relational database managers ( such as Informix > Online - but NOT Informix Standard Engine ) guarantee that logical > groups of physical disk operations are handled in an all or nothing > fashion. This is done by means of logs (like the Online Physical > Log) automatic checkpoint procedures and automatic recovery procedures > (like the Online Fast Recovery) that are invoked whenever the database > manager starts up. Just so's I understand this properly, could I ask you to read this ? We're assuming 4GL and a logged SE DB (C-ISAM) , of course. # SNIP, SNIP BEGIN WORK DELETE FROM foo WHERE bar > 5 IF status < 0 THEN LET my_err_flag = 1 END IF IF my_err_flag = 0 THEN DELETE FROM bar WHERE foo > 3 IF status < 0 THEN LET my_err_flag = 1 END IF END IF IF my_err_flag = 1 THEN ROLLBACK WORK ELSE COMMIT WORK END IF # SNIP, SNIP Okay, so if it goes all the way thru, the checks on status are perfectly satisfactory, but if I flick the juice off half way thru one of the DELETEs the DB's trashed ? At that point, can one restore the backup and do a rollforward, or does one lose the log as well ? Sounds like the answer might be a UPS, a signal handler around the sensitive bits and a strict ban on kill -9's on the backends. Shame about the UPS ... SE does a rollback if the front end dies, on a logged DB ? So a DEL/^C type of user interrupt shouldn't do too much damage ? Incidentally (non-DHLers), we run a large number of applications on C-ISAM (Unibol System/36 environment) under Unix and I very rarely hear of busted files. Admittedly, the Unix shutdown is (usually) done fairly gently. > Unfortunately, it is difficult to get MSDOS users not to > turn off the machine whenever they feel like it. Something to do with having a BIG RED ATTENTION GRABBING SWITCH, maybe 8^) > ------------ DHL WORLDWIDE EXPRESS ------------------------------------------ > Greg Bryan gbryan@ssf-sys.dhl.com DHL Systems > Data Administrator uunet!ssf-sys.dhl.com!gbryan San Francisco > ------------------------------------------------------------------------------ Thanks for the information, sorry about all the questions. Cheers - Tony. ____________________________________________________________________________ Who: Tony Heskett | DHL Systems Ltd, Kings House, How: theskett@lhr-sys.ssf-sys.dhl.com | Great West Road, Brentford, TW8 9HS Vox: (+44) 81 747 8330 x 363 | Fax: (+44) 81 747 0875