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16 lines
1.1 KiB
TeX
16 lines
1.1 KiB
TeX
Cloud systems need to be very reliable, no data is allowed to be lost.
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In basic versions of so-called \bi{shared nothing instances}, this is not as much guaranteed as it should be,
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because all DBs systems have their own disks and they don't replicate or exchange their data.
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To improve fault tolerance, make blocks small, like 1MB and replicate each block on a different compute node and ideally on a separate S3 node,
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which serves as a backup. That's the 3-2 taken care of of the 3-2-1 backup strategy. This should then also be replicated off-site to mitigate the risk of destruction of all nodes
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from a natural disaster, building collapse, fire or similar.
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Modern clouds separate compute and storage entirely. Typically, compute servers have no disk and are booted using iSCSI,
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or they have a small disk for the base operating system in them.
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In systems with disaggregated Compute, Memory and Storage, each layer can scale independently, allowing large memory shuffles to take place and allows
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for larger numbers of blocks for sorting and joins, which, as we have seen, can massively boost performance.
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The Big Query system is one such example.
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