Replication
Keeping several copies of data: the primary and its replicas, synchronous or asynchronous, replication lag, failover, and why a replica is not a backup.
- 34 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
Replication: what is it?
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Keeping copies of the same data on several servers.
You gain availability and read capacity.
The database saturates on reads, writes stay low. What do you do?
- Add read replicas
- Shard
- Switch to synchronous
- Drop indexes
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Add read replicas
Each replica takes its share of the reads.
Primary (leader): what is it?
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The server that accepts writes and passes them to the replicas.
A single primary avoids two servers writing different versions.
With asynchronous replication, the primary fails suddenly. What risk?
- Losing committed writes not yet copied
- None
- Losing all history
- Blocking reads forever
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Losing committed writes not yet copied
What the replica had not received exists nowhere else.