On 6/11/19 11:15 AM, Karsten Hilbert wrote:
The problem I hope to protect against with this approach: the
CREATE DATABASE might untaint corrupted data from a bad disk
block into a good disk block virtue of doing a file level
copy.
I hope my reasoning isn't going astray.
As I understand it checksums are done on the page level using a hash(for
details: https://doxygen.postgresql.org/checksum__impl_8h_source.html).
I am not sure how a page could get un-corrupted by virtue of a file copy.
Ah, no, I did not explain myself well.
Let's assume a corrupted, bad (but readable at the hardware
level) disk block B. A filesystem level copy (as in CREATE
DATABASE) would successfully read that disk block B and
copy the corrupted content into a good disk block G elsewhere
on the disk. Verifying the checksum of the page sitting on
block B before doing the database cloning would
reveal the corruption before it got cloned.
Does that make sense ?
Yes.
Karsten
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
