Databases
Choosing, indexing, replicating and splitting databases: SQL vs NoSQL, transactions, replication, sharding, consistent hashing, tuning and object storage.
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Module 06
Databases
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6.1
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SQL vs NoSQL: How to Choose
Relational databases give you tables, joins and transactions; NoSQL databases trade some of that for flexible data models and easy horizontal scaling. Learn the real differences and a simple way to choose.
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6.2
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Database Indexes
An index lets the database find rows without reading the whole table, turning seconds into milliseconds. Learn how B-tree and LSM-tree indexes work, composite indexes, and when an index makes things worse.
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6.3
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Transactions, ACID and Isolation Levels
A transaction groups several changes so they all happen or none do. Learn what ACID guarantees, how BASE differs, the anomalies each isolation level allows, and how to avoid lost updates.
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6.4
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Database Replication
Replication keeps copies of your data on several machines for availability and read capacity. Learn leader-follower and multi-leader setups, synchronous vs asynchronous copies, replication lag and failover.
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6.5
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Sharding (Partitioning)
Sharding splits one big dataset across several databases so each holds a slice. Learn range, hash and directory sharding, how to choose a shard key, hot keys, cross-shard queries and resharding.
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6.6
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Consistent Hashing
Consistent hashing places servers and keys on a ring, so adding or removing a server moves only a small share of the keys. Learn how the ring works, why virtual nodes matter, and where it is used.
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6.7
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Federation (Functional Partitioning)
Federation splits one database into several by feature: users in one, products in another, orders in a third. Learn what it buys you, what it costs, and how it differs from sharding.
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6.8
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Denormalization
Denormalization stores copies or precomputed results so reads skip expensive joins and counts. Learn when it pays off, the common forms (copied columns, counters, materialized views) and how to keep copies in sync.
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6.9
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SQL Tuning
Most slow databases are slow because of a handful of queries. Learn to find them, read query plans, and fix the usual suspects: missing indexes, N+1 queries, SELECT *, deep OFFSET pagination and too many connections.
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6.10
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NoSQL Types: Key-Value, Document, Wide-Column, Graph
NoSQL is not one thing. Key-value, document, wide-column and graph databases each fit different data and queries. Learn how each models data, what it is good at, and where it struggles.
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6.11
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Blob and Object Storage
Images, videos, backups and uploads do not belong in your database or on a web server's disk. Learn how object storage works, how clients upload directly with presigned URLs, and how to serve files through a CDN.