Relational databases
Tables, indexes, transactions and ACID guarantees: how a relational database stays correct and fast, and what to know so as not to slow it down or corrupt it.
- 33 cards
- 3 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Scenarios
- Trade-offs and failures
A few cards from the deck
Index: what is it?
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A structure, often a B-tree, that finds rows without scanning the whole table.
Filtered reads become fast, but every write must also update the index.
The query « WHERE email = ? » is slow on 10 million rows. What do you do?
- An index on the email column
- More memory on the web server
- The browser cache
- Shard the users
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An index on the email column
Without an index the database scans every row; with one it goes straight to the right ones.
Transaction: what is it?
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A set of operations run as a whole: everything is committed, or everything is rolled back.
The database is never left half modified.
You add ten indexes on a heavily written table. Consequence?
- Slower writes and more disk space
- Slower reads
- None
- Rolled-back transactions
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Slower writes and more disk space
Each insert or update must update every index.