Systems for structured storage, retrieval, and manipulation of data. Persistent memory for computation.
models
relational: tables with rows and columns, SQL, joins, normalization. PostgreSQL, MySQL
graph: nodes and edges as first-class citizens, Cypher/SPARQL queries. Neo4j, knowledge graphs
key-value: simple pairs, high throughput. Redis, RocksDB
document: JSON/BSON documents, flexible schema. MongoDB, CouchDB
column-family: wide columns, optimized for reads at scale. Cassandra, HBase
fundamentals
indexing: B-trees, hash indexes, inverted indexes for fast lookup
ACID: atomicity, consistency, isolation, durability -- transaction guarantees
CAP theorem: a distributed database can guarantee at most two of consistency, availability, and partition tolerance
query optimization: transforming queries into efficient execution plans using algorithms
distributed databases
Sharding, replication, and consensus algorithms enable databases to scale across nodes. cyber uses distributed storage for the knowledge graph.