On 3/7/13 9:31 PM, Bruce Momjian wrote:
1 storage
2 storage controller
3 file system
4 RAM
5 CPU
I would add 2.5 in there: storage interconnect. iSCSI, FC, what-have-you.
Obviously not everyone has that.
My guess is that storage checksums only cover layer 1, while our patch
covers layers 1-3, and probably not 4-5 because we only compute the
checksum on write.
Actually, it depends. In our case, we run 512GB servers and 8GB shared buffers
(previous testing has shown that anything much bigger than 8G hurts
performance).
So in our case, PG checksums protect a very significant portion of #4.
If that is correct, the open question is what percentage of corruption
happens in layers 1-3?
The last bout of corruption we had was entirely coincident with memory
failures. IIRC we had 3-4 corruption events on more than one server. Everything
was running standard ECC (sadly, not 4-bit ECC).
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