Testing failover to one of 2 slaves and reattaching to the new master.
Starting config
master | | slave1 slave2
Post failover config
slave1 | | slave2 master
What is apache Cassandra?
Cassandra is a fast distributed database.
It has several defining features:
- Built in high availability. – Any node can handle read and write requests and your data is replicated to x nodes so regardless of which node (or even a data center) goes down, you will still have access to read and write your data.
- Linear Scalability. – Doubling the number of (identical) nodes should double the write performance. Its basically as simple as that was all nodes can handle all operations and there is no central control.
- Predictable performance. (i.e. doubling the number of identical nodes should double the write throughput)
- no single point of failure. -nodes can go down and come back up without the front end application becoming aware of it.
- Multiple Data Centres catered for and taken advantage of out as standard.
- Built to run on commodity hardware – so you can run it on lots of $1000 servers rather than 1 or 2 $100000 servers.
- Easy to manage operationally. – The system is designed to need very little ops input.
Relational Databases and Big Data workloads.
This intro to Cassandra is taken from the DataStax course. I don’t necessarily agree with everything – particularly their take on what a traditional RDBMS can and can’t do but I have included their view here for completeness.
Cassandra is designed for ‘Big Data’ workloads. Im order to understand the characteristics of Big Data, lets first define ‘Small Data’:
This would typically be a volume of storage that would fit on 1 machine and a RDBMS is typically fine and able to handle the number of operations and the quantity of data. The system will support a number of concurrent users in the hundreds. It fully supports ACID.
When you want to scale such a system, you are going to do it vertically first – with a bigger host, more RAM or processors.
Can Relational databases support big data?
Get all of the tables linked by a Foreign Key
Here is a handy little PostgreSQL query that will list all of the tables linked by a foreign key to the table YOUR_TABLE. The output will include the keys on each side. This can be very useful if you want to build up a map of your database through the relationships between the tables. select …
How to kill all sessions in Postgres so that they stay dead.
Have you ever tried to drop or rename a postgres database or even create another database from one as a template, only to be confronted by the dreaded message: postgres=# create database test with template a_database; ERROR: source database “a_database” is being accessed by other users DETAIL: There are 40 other sessions using the database. …
How to make a Decision
I am slightly embarrassed to admit that I have often avoided making decisions throughout my life. That’s not to say that I haven’t made things happen but I have often avoided putting my foot down and choosing a path one way or the other, preferring instead to allow circumstances to make the decision myself. That’s not to say that I haven’t subconsciously pushed circumstances one way or another, but it’s not the same and does not give you the same benefits as being decisive and telling the world what you want.
The thing is that an argument could be made that the whole point of life is to make decisions (if we take any spiritual questions out of the equation). The biological definition of life is that ‘life is irritable’ meaning that the environment does something and life does something back. This is true for all life – a plant decides on some level to move towards the light and if it were to stop doing it, it would die. The same is true for us on a much more complex level. If we were to stop making decisions, we would not get up, eat or drink and we would soon die.
How to live 10 Years Longer by Playing Games
Plus be happier and have fewer regrets
“I’m a gamer so I like to have goals. I like special missions and secret objectives, so here’s my special mission for this talk. I’m going to try to increase the lifespan of everyone in this room by seven and a half minutes.”
– Jane McGonigal
Jane Mcdonigal gave a talk at TED recently that I loved. Its backed by some real research and gives us a way to not only live longer but to enjoy life while we live it and to avoid the top 5 deathbed regrets which are:
Top 5 deathbed regrets:
How to instantly be more powerful and feel better about yourself.
The cheaters guide to being more powerful, confident and becoming the person you wish you could be (and living longer as a bonus).Its quite a promise but you will easily get that and a lot more from this short post and video.
A word of warning though is that you get absolutely no benefit whatsoever from this until you physically do it. On the plus side there is nothing easier to test and you can immediately feel the benefits. What even better is that the more that you do it, the greater the benefit that you get and the more ingrained the changes will become.
What is an Oracle Service
Oracle services were a feature introduced in Oracle 10g. Their function is to simplify workload management by allowing you to group applications that share traits such as thresholds, priorities and attributes. The Oracle database is presented as a service and so you always have at least one service running. It is good practice to create …
Oracle ASM Mirroring and Failure groups.
Oracle ASM keeps redundancy quite simple by providing only 3 options. you can choose to have no redundancy or mirroring provided by the ASM instance. This is the ‘External’ option and assumes that you are handling mirroring somewhere else perhaps through hardware raid on your storage network. You can chose ‘normal’ 2 way mirroring r …