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.
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