Grokking the System Design Interview
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PACELC Theorem

The CAP Theorem describes one moment: the moment the network between your machines breaks. During that moment a system chooses between consistency and availability.

Partitions are rare. So CAP says nothing about almost all of the time your system is running. That is a large gap, and PACELC fills it.

PACELC says that if there is a Partition (P), the system trades off between Availability (A) and Consistency (C). Else (E), when the network is healthy, the system trades off between Latency (L) and Consistency (C).

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Omar Qunsul

· 21 days ago

ACID (Atomicity, Consistency, Isolation, Durability) databases, such as RDBMSs like MySQL, Oracle, and Microsoft SQL Server, chose consistency (refuse response if it cannot check with peers)

What does this have to do with distributed systems and the CAP theory?

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rahul.raja412

· 3 years ago

Key-Value : Redis, voldemort, Dynamo

Document : CouchDB, MongoDB

Wide column : Cassandra, HBase

Graph: Neo4J, InfiniteGraph

Dynamo, Cassandra : chooses availability and lower latency over Consistency : Uses Consistent Hashing

BigTable, HBase : Chooses consistency

MongoDB : Configurable : Default : Primary/secondaries Configuration: PA/EC

Custom : if asked to write on Majority replicas and read from the primary - PC/EC

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