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Re: pg_dump include/exclude data, was: verify checksums / CREATE DATABASE

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On 6/11/19 12:15 AM, Karsten Hilbert wrote:
Dear Adrian,

Sure, but that much depends on what (or rather, where) the
"new cluster" actually is.

In my case I want to make sure that - before a run of "CREATE
DATABASE new TEMPLATE old" - I can be reasonable sure that
the disk blocks underlying "old" verify against their
checksum. Since the CREATE DATABASE does not verify CRCs I
use a pg_dump into /dev/null to verify checksums while the
cluster is *online*.

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.



One will be tempted to include options to speed up the
process, say:
...
Is my assumption wrong ?

Not sure, though it would seem to me including the above is a relatively
small incremental cost to the overall dump, assuming a data set of any size
greater then small.

Agreed. Good putting of things into perspective. Will do.

Thanks,
Karsten
--
GPG  40BE 5B0E C98E 1713 AFA6  5BC0 3BEA AC80 7D4F C89B



--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx





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