Database Replication with Slony-I
Listing 4. promote.sh
#!/bin/bash CLUSTER=sql_cluster H1=master.example.com H2=slave.example.com U=postgres DB1=contactdb DB2=contactdb su - postgres -c slonik <<_EOF_ cluster name = $CLUSTER; node 1 admin conninfo = 'dbname=$DB1 host=$H1 user=$U'; node 2 admin conninfo = 'dbname=$DB2 host=$H2 user=$U'; failover (id = 1, backup node = 2); drop node (id = 1, event node = 2);
From Listing 4, the failover Slonik command is used to indicate that the node with id = 1, the node running on master.example.com, has failed, and that the node with id = 2 will take over all sets from the failed node. The second command, drop node, is used to remove the node with id = 1 from the replication system completely. Eventually, you might want to bring back the failed node in the cluster. To do this, you must configure it as a slave and let Slony-I replicate any missing information. Eventually, you can proceed with a switchback to the initial master node by locking the set (lock set), waiting for all events to complete (wait for event), moving the set to a new origin (move set) and waiting for a confirmation that the last command has completed. Please refer to the Slonik Command Summary for more information on those commands.
Replicating databases using Slony-I is relatively simple. Combined with the Linux-HA Heartbeat, this allows you to offer high availability of your database services. Although the combination of Slony-I and Linux HA-Heartbeat is an attractive solution, it is important to note that this is not a substitute for good hardware for your database servers.
Even with its small limitations, like not being able to propagate schema changes or replicate large objects, Slony-I is a great alternative to both rserv and ERServer and is now, in fact, the preferred solution for replicating PostgreSQL databases. Slony-II even supports synchronous multimaster replication and is already on the design table.
To conclude, I would like to thank Jan Wieck, the author of Slony-I, for reviewing this article.
Resources for this article: /article/8202.
Ludovic Marcotte (firstname.lastname@example.org) holds a Bachelor's degree in Computer Science from the University of Montréal. He is currently a software architect for Inverse, Inc., an IT consulting company located in downtown Montréal.
Fast/Flexible Linux OS Recovery
On Demand Now
In this live one-hour webinar, learn how to enhance your existing backup strategies for complete disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible full-system recovery solution for UNIX and Linux systems.
Join Linux Journal's Shawn Powers and David Huffman, President/CEO, Storix, Inc.
Free to Linux Journal readers.Register Now!
- The Italian Army Switches to LibreOffice
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- Linux Mint 18
- Oracle vs. Google: Round 2
- The FBI and the Mozilla Foundation Lock Horns over Known Security Hole
- Devuan Beta Release
- Varnish Software's Varnish Massive Storage Engine
- Privacy and the New Math
- Ben Rady's Serverless Single Page Apps (The Pragmatic Programmers)
Until recently, IBM’s Power Platform was looked upon as being the system that hosted IBM’s flavor of UNIX and proprietary operating system called IBM i. These servers often are found in medium-size businesses running ERP, CRM and financials for on-premise customers. By enabling the Power platform to run the Linux OS, IBM now has positioned Power to be the platform of choice for those already running Linux that are facing scalability issues, especially customers looking at analytics, big data or cloud computing.
￼Running Linux on IBM’s Power hardware offers some obvious benefits, including improved processing speed and memory bandwidth, inherent security, and simpler deployment and management. But if you look beyond the impressive architecture, you’ll also find an open ecosystem that has given rise to a strong, innovative community, as well as an inventory of system and network management applications that really help leverage the benefits offered by running Linux on Power.Get the Guide