Database High Availability Using SHADOW Systems

Best paper award in ACM Symposium on Cloud Computing 2015

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Free you Active node (a.k.a. Primary, Master) from database writing overhead.

Various High Availability DataBase systems (HADB) are used to provide high availability.
Pairing an active database system with a standby system is one commonly used HADB
techniques. The active system serves read/write workloads. One or more standby systems
replicate the active and serve read-only workloads. Though widely used, this technique has
some significant drawbacks: The active system becomes the bottleneck under heavy write
workloads. Replicating changes synchronously from the active to the standbys further
reduces the performance of the active system. Asynchronous replication, however, risk the
loss of updates during failover. The shared-nothing architecture of active-standby systems
is unnecessarily complex and cost inefficient.

We present SHADOW systems, a new technique for database high availability.
In a SHADOW system, the responsibility for database replication is pushed from
the database systems into a shared, reliable, storage system. The active and standby systems
share access to a single logical copy of the database, which resides in shared storage.
SHADOW introduces write offloading, which frees the active system from the need to
update the persistent database, placing that responsibility on the underutilized standby
system instead. By exploiting shared storage, SHADOW systems avoid the overhead of
database-managed synchronized replication, while ensuring that no updates will be lost
during a failover. We have implemented a SHADOW system using PostgreSQL, and we
present the results of a performance evaluation that shows that the SHADOW system can
outperform both traditional synchronous replication and standalone PostgreSQL systems.