+ linkend="creating-cluster-nfs">). One significant limitation of this
+ method is that if the shared disk array fails or becomes corrupt, the
+ primary and standby servers are both nonfunctional. Another issue is
+ that the standby server should never access the shared storage while
the primary server is running.
+
+
+
+
+ File System Replication
+
+
A modified version of shared hardware functionality is file system
replication, where all changes to a file system are mirrored to a file
- Warm Standby Using Point-In-Time Recovery
+
Warm Standby Using Point-In-Time Recovery (PITR>)
+
+ Asynchronous Multi-Master Replication
+
+
+ For servers that are not regularly connected, like laptops or
+ remote servers, keeping data consistent among servers is a
+ challenge. Using asynchronous multi-master replication, each
+ server works independently, and periodically communicates with
+ the other servers to identify conflicting transactions. The
+ conflicts can be resolved by users or conflict resolution rules.
+
+
+
+
Synchronous Multi-Master Replication
-
- Asynchronous Multi-Master Replication
-
-
- For servers that are not regularly connected, like laptops or
- remote servers, keeping data consistent among servers is a
- challenge. Using asynchronous multi-master replication, each
- server works independently, and periodically communicates with
- the other servers to identify conflicting transactions. The
- conflicts can be resolved by users or conflict resolution rules.
-
-
-
-
Data Partitioning
-
- Multi-Server Parallel Query Execution
-
-
- Many of the above solutions allow multiple servers to handle
- multiple queries, but none allow a single query to use multiple
- servers to complete faster. This solution allows multiple
- servers to work concurrently on a single query. This is usually
- accomplished by splitting the data among servers and having
- each server execute its part of the query and return results
- to a central server where they are combined and returned to
- the user. Pgpool-II has this capability.
-
-
-
-
Commercial Solutions
+ The table below () summarizes
+ the capabilities of the various solutions listed above.
+
+
+
+
High Availability, Load Balancing, and Replication Feature Matrix
+
+
+ |
+ Feature
+ Shared Disk Failover
+ File System Replication
+ Warm Standby Using PITR
+ Master-Slave Replication
+ Statement-Based Replication Middleware
+ Asynchronous Multi-Master Replication
+ Synchronous Multi-Master Replication
+ Data Partitioning
+
+
+
+
+
+ |
+ No special hardware required
+
+ •
+ •
+ •
+ •
+ •
+ •
+ •
+
+
+ |
+ Allows multiple master servers
+
+
+
+
+ •
+ •
+ •
+
+
+
+ |
+ No master server overhead
+ •
+
+ •
+
+
+
+
+
+
+
+ |
+ Master server never locks others
+ •
+ •
+ •
+ •
+ •
+ •
+
+ •
+
+
+ |
+ Master failure will never lose data
+ •
+ •
+
+
+ •
+
+ •
+
+
+
+ |
+ Slaves accept read-only queries
+
+
+
+ •
+ •
+ •
+ •
+ •
+
+
+ |
+ Per-table granularity
+
+
+
+ •
+
+ •
+ •
+ •
+
+
+ |
+ No conflict resolution necessary
+ •
+ •
+ •
+ •
+
+
+ •
+ •
+
+
+
+
+
+
+ Many of the above solutions allow multiple servers to handle multiple
+ queries, but none allow a single query to use multiple servers to
+ complete faster. Multi-server parallel query execution allows multiple
+ servers to work concurrently on a single query. This is usually
+ accomplished by splitting the data among servers and having each server
+ execute its part of the query and return results to a central server
+ where they are combined and returned to the user. Pgpool-II has this
+ capability.
+
+