MySQL Database Corruption (InnoDB), according to Innodb Hot Backup

[David Griffiths]

I went to do some work on our database last night (dropping large 
indexes, which can be time consuming). I checked to ensure that the 
backup of that evening had run, but noticed that the size of the backup 
was too small compared to previous days (I'm kicking myself for not 
emailing the results of the backup to myself every night - I just have a 
job that verifies that the backup actually ran).

So I ran the backup by hand. We have 8 data files, the first 7 being 4 
gig in size, and the last being a 10-meg autoextend. This is MySQL 
4.0.20 64bit, running on a dual Opteron machine running SuSE 8 
Enterprise (64-bit). We are using ibbackup 2.0 beta (which is 64-bit for 
the Opteron).

ibbackup (the Innodb backup utility) complains on the first file.
ibbackup: Re-reading page at offset 0 3272818688 in 
/usr/local/mysql/var/ywdata1

this repeats a few hundred times
Then it dumps some ascii:
040930 11:44:14  InnoDB: Page dump in ascii and hex (16384 bytes):
len 16384; hex 55c3ee4d00030c4d00030c4c000374.....
And at the bottom,
040930 11:44:14  InnoDB: Page checksum 1522485550, prior-to-4.0.14-form 
checksum 1015768137
InnoDB: stored checksum 1438903885, prior-to-4.0.14-form stored checksum 
4028531590
InnoDB: Page lsn 3 1070601164, low 4 bytes of lsn at page end 1070609127
InnoDB: Page number (if stored to page already) 199757,
InnoDB: space id (if created with >= MySQL-4.1.1 and stored already) 0
InnoDB: Page may be an index page where index id is 0 680
ibbackup: Error: page at offset 0 3272818688 in 
/usr/local/mysql/var/ywdata1 seems corrupt!

While we no longer seem to have a backup, we do have a slave (not sure 
if the corruption propigated to the slave; I know it can happen in Oracle).

I have a few questions:
1) Is InnoDB backup correct? This might be a false positive (doubt it 
though).

2) What are the risks of stopping and starting the database? There is a 
force-recovery option in inndb, which might fix the corruption. Note 
that I answered this myself. I ran a "check table" on one of our larger 
tables (600,000 rows) which killed the database. It came back up fine. I 
re-ran the backup - same issue, with the same page checksums, etc.

3) Anyone have any experience with this? Keep in mind that this might be 
an Opteron/MySQL-64bit issue. Or it might be a general issue in MySQL.

Thanks,
David
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