# High Availability User's Guide

> eXtremeDB High Availability is McObject's in-memory and on-disk embedded database solution for applications such as network and telecom gear that require the highest degree of reliability.

> The following topics explain the general principles of eXtremeDB High Availability application design and implementation:

> Introduction | How eXtremeDB High Availability maintains multiple identical database instances within separate address spaces
> Theory of operation | Explanation of reliable failover processes and high availability data stores
> Overview | The eXtremeDB High Availability synchronous replication uses a time-cognizant two-phase commit replication protocol
> HA Applications | The eXtremeDB High Availability two-layered architecture facilitates application development
> Synchronization | "Static", "Hot" and "Stateful" synchronization
> Synchronous Replication | Detailed explanation of eXtremeDB High Availability synchronous replication implementation
> Asynchronous Replication | Detailed explanation of eXtremeDB High Availability asynchronous or lazy replication implementation
> HA Implementation Details | Mixing Synchronous and Asynchronous Replication, Replication with a Persistent Database, Multiple Communication Channels, Partial Replication and Distributed Processing
> Dynamic schema modification | Modifying an SQL database schema with SQL DDL statements `create table/index`, `drop table/index` and `alter table/index`
> OpenSSL Integration | The eXtremeDB High Availability Transport Layer Secure Sockets Layer security (TLS/SSL) implemented with OpenSSL
> Optimizations | Techniques and tips for optimizing eXtremeDB High Availability application performance