ClearDB

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ClearDB is a distributed, cloud-hosted, database-as-a-service version of MySQL. Its primary purpose is to eliminate the management cost of MySQL databases and provide automatic database replication and failover. By adding software stacks on top of MySQL and leveraging geo-separated data clusters, ClearDB is able to guarantee 100% uptime. ClearDB supports major commercial cloud which includes Amazon EC2 and Windows Azure and also support customized data centers or a hybrid of the two.

Checkpoints

Fuzzy

It uses both Fuzzy and Sharp checkpoint. It takes a sharp checkpoint when the database is performing shut down and uses fuzzy checkpoint during normal database operations.

Data Model

Relational

Concurrency Control

Two-Phase Locking (Deadlock Detection)

MySQL uses a combination of Multiversion Concurrency Control (MVCC) and row-level locking to achieve better concurrency. Old versions of rows are stored in a rollback segment which could later be used to rollback changes. Rollback segments are partitioned into the insert and update undo logs for different types of rollbacks.

Compression

Naïve (Page-Level)

InnoDB supports multiple compression algorithms which include Zlib and LZ4. When writing a page to disk, data were first compressed and then written to disk. Then empty blocks will be released by hole punching mechanism.