# Sre
All Sre notes →1 — Relational Databases
ACID guarantees, transaction isolation levels, and the reliability characteristics an SRE inherits the moment a service depends on one.
2 — NoSQL Systems
The consistency, availability, and schema trade-offs different NoSQL models make, and why 'NoSQL' is really a dozen different reliability postures wearing one name.
3 — Distributed Databases
How a database spreads data and consensus across nodes, and the CAP-theorem trade-off it's making on your behalf whether or not that's documented.
4 — Replication
Synchronous vs. asynchronous replication, and the replication-lag failure mode that turns a 'read your own write' assumption into an intermittent bug report.
5 — Sharding
Partitioning data across nodes to scale past a single machine's limits, and the resharding operation that's usually the actual hard part.
6 — Backup Strategies
Full, incremental, and snapshot backups, and the retention policy that has to balance recovery granularity against storage cost.
7 — Recovery Strategies
Restoring from a backup is the easy half — validating the restored data is actually correct and current is the half most recovery plans skip until it matters.
8 — Data Reliability
Durability, consistency, and corruption detection as their own reliability discipline, distinct from the service-availability SLOs the rest of this book focuses on.