Availability
A 99.99% target can limit failed requests or downtime. The population, success rule, and measurement window determine what that percentage promises.
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SLIs, SLOs, and Error Budgets
A reliability target needs a measurement boundary, a reason, and a response to failure. Learn how SLIs, SLOs, and error budgets support that decision.
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Unclean Leader Election
When no safe leader candidate remains, unclean election can restore availability from a lagging replica while losing acknowledged records. Check ISR and eligible leader replicas.
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Quorum
A quorum sets how many replicas must respond. Overlap gives read and write sets a shared replica, while retention and version-selection rules determine what a read returns.
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CAP Theorem
CAP forbids perfect consistency with perfect availability during a partition — a narrower claim than the “pick two of three” framing suggests.
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Quality Attributes and Trade-offs
Fast, reliable, and scalable mean different things to different teams. Define each quality precisely, measure it, and see where improving one costs another.