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

From pgsql@mohawksoft.com
Subject Re: Block-level CRC checks
Date
Msg-id 47015.71.232.149.185.1222809205.squirrel@mail.mohawksoft.com
Whole thread Raw
In response to Re: Block-level CRC checks  (Decibel! <decibel@decibel.org>)
Responses Re: Block-level CRC checks  (Hannu Krosing <hannu@2ndQuadrant.com>)
List pgsql-hackers
>
> I believe the idea was to make this as non-invasive as possible. And
> it would be really nice if this could be enabled without a dump/
> reload (maybe the upgrade stuff would make this possible?)
> --

It's all about the probability of a duplicate check being generated. If
you use a 32 bit checksum, then you have a theoretical probability of 1 in
4 billion that a corrupt block will be missed (probably much lower
depending on your algorithm). If you use a short, then a 1 in 65 thousand
probability. If you use an 8 bit number, then 1 in 256.

Why am I going on? Well, if there are any spare bits in a block header,
they could be used for the check value.


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