Re: Block-level CRC checks - Mailing list pgsql-hackers

From Heikki Linnakangas
Subject Re: Block-level CRC checks
Date
Msg-id 4B14CDF7.7030508@enterprisedb.com
Whole thread Raw
In response to Re: Block-level CRC checks  (Simon Riggs <simon@2ndQuadrant.com>)
Responses Re: Block-level CRC checks  (Simon Riggs <simon@2ndQuadrant.com>)
List pgsql-hackers
Simon Riggs wrote:
> There is no "creation" of corruption events. This scheme detects
> corruption events that *have* occurred. Now I understand that we
> previously would have recovered seamlessly from such events, but they
> were corruption events nonetheless and I think they need to be reported.
> (For why, see Conclusion #2, below).

No, you're still missing the point. The point is *not* random bit errors
affecting hint bits, but the torn page problem. Today, a torn page is a
completely valid and expected behavior from the OS and storage
subsystem. We handle it with full_page_writes, and by relying on the
fact that it's OK for a hint bit set to get lost. With your scheme, a
torn page would become a corrupt page.

--  Heikki Linnakangas EnterpriseDB   http://www.enterprisedb.com


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