Re: Enabling Checksums

On 04.03.2013 22:51, Jim Nasby wrote:
> Additionally, no filesystem I'm aware of checksums the data in the
> filesystem cache. A PG checksum would.

The patch says:

> + * IMPORTANT NOTE -
> + * The checksum is not valid at all times on a data page. We set it before we
> + * flush page/buffer, and implicitly invalidate the checksum when we modify the
> + * page. A heavily accessed buffer might then spend most of its life with an
> + * invalid page checksum, so testing random pages in the buffer pool will tell
> + * you nothing. The reason for this is that the checksum detects otherwise
> + * silent errors caused by the filesystems on which we rely. We do not protect
> + * buffers against uncorrectable memory errors, since these have a very low
> + * measured incidence according to research on large server farms,
> + * http://www.cs.toronto.edu/~bianca/papers/sigmetrics09.pdf, discussed 2010/12/22.

It's still true that it does in fact cover pages in the filesystem
cache, but apparently that's not important.

- Heikki