Database Server administration concepts for Architects/ Tech Leads/ Database developers

Most of us must have heard of Database replication/ mirroring but few of us would have tried to explore the details. This article explains about these concepts which would give you an overall understanding of Database server concepts which are used for large applications.


What is Database Mirroring?

Database mirroring is a primarily software solution for increasing database availability.
It maintains two copies of a single database that must reside on different server instances of SQL Server Database Engine.

What is Database Replication?

It is a set of technology for copying and distributing data and database objects from one database to another and then synchronizing between databases to maintain consistency. Using replication, you can distribute data to different locations and to remote or mobile users over local and wide area networks, dial-up connections, wireless connections, and the Internet.

Most of the development community think that above two mentioned questions are enough for database backups/ availability. There is yet another way which is most popular among the Database administrator's which is "Log Shipping".

So what is Log shipping?

It is sending transaction log backups from one database (Primary database) to another (Secondary database) on another server. An optional third server known as Monitor server records the history and status of the backups and restore operations. 

Server limitations for above mentioned techniques

Log Shipping --> It can be configured as One to Many. i.e one primary server and many                                secondary servers. 

                        Or
                        Secondary server can contain multiple Primary databases that are log                               shipped from multiple servers.
Mirroring      --> It's one to one. i.e., One principal server to one mirror server.
Replication  -->

• Central publisher/distributor, multiple subscribers.
• Central Distributor, multiple publishers, multiple subscribers.
• Central Distributer, multiple publishers, single subscriber.
• Mixed Topology.

Backup/ Restoration

Log Shipping -->This can be done manually or through Log Shipping options.
Mirroring      --> User take backup & restore manually.
Replication  --> User creates an empty database with the same name.

Note: If you see any corrections or have suggestions please do let me know.

UML Part I

UML Intro

UML stands for Unified Modeling Language. UML is a graphical language for visualizing, specifying, constructing & documenting the artifacts of a software system. It is a standard language for designing and documenting a system in an object oriented manner. UML provides blue print for Business process, System functioning, programming language statements, Database schema & reusable components.

UML is used in all phases of software development from Requirement Specification to Acceptance Test and from Designing a solution to Deploying/ Packaging. Modeling has been around for years not only in software field but also in other fields like Civil, Mechanical, etc. we get a model ready & approved before starting the production. Modeling makes complex system to break up into simple and discrete pieces that be individually understood. If we ask ourselves have we been doing/ following modeling, most of us would say NO. But all of us do modeling, the flowchart that we draw is a model for your module isn't it.

Now we should see what are the advantages of modeling:

1. Readability: Representing the whole architecture in flowcharts, class diagrams, state diagrams, ER diagrams, etc. makes our project more readable. Especially when we have programmer's changing job, handover becomes easier.
2. Re-usability: Once the system is readable and broken down to pieces, it becomes easier to identify redundant and similar modules. Thus increasing re-usability. We can decide of reusable components to be used across the application.Why shall we adopt UML?

Well different languages have different ways of coding and syntax's. In order to bring all languages under one roof UML comes into picture. As the term comes in UNIFIED, it unifies all different languages in one roof so people who are working on some other platforms can understand that.

There was an interesting question put up “Does UML fit in Agile/Scrum environment?” during a UML session presented by myself & one of my colleague at our office CastleRock, Kolkata.
Well the answer is yes, UML is not a methodology dependent you can apply it to any of the software development process. If we have a blueprint of the whole architecture, whenever we are required to make changes or alter a section/ module we can very easily trace which all sections/ modules would get effected & at the same time you can figure out how much time it might take to finish the job.

You can checkout the list of UML tools at http://www.sereferences.com/uml-tools.php.

In the next post I will cover different UML diagrams.

UML: UML Intro UML stands for Unified Modeling Languag...

 UML INTRO

UML stands for Unified Modeling Language. UML is a graphical language for visualizing, specifying, constructing & documenting the artifacts of a software system. It is a standard language for designing and documenting a system in an object oriented manner. UML provides blue print for Business process, System functioning, programming language statements, Database schema & reusable components.

UML is used in all phases of software development from Requirement Specification to Acceptance Test and from Designing a solution to Deploying/ Packaging. Modeling has been around for years not only in software field but also in other fields like Civil, Mechanical, etc. we get a model ready & approved before starting the production. Modeling makes complex system to break up into simple and discrete pieces that be individually understood. If we ask ourselves have we been doing/ following modeling, most of us would say NO. But all of us do modeling, the flowchart that we draw is a model for your module isn't it.

Now we should see what are the advantages of modeling:

1. Readability: Representing the whole architecture in flowcharts, class diagrams, state diagrams, ER diagrams, etc. makes our project more readable. Especially when we have programmer's changing job, handover becomes easier.
2. Re-usability: Once the system is readable and broken down to pieces, it becomes easier to identify redundant and similar modules. Thus increasing re-usability. We can decide of reusable components to be used across the application.Why shall we adopt UML?

Well different languages have different ways of coding and syntax's. In order to bring all languages under one roof UML comes into picture. As the term comes in UNIFIED, it unifies all different languages in one roof so people who are working on some other platforms can understand that.

There was an interesting question put up “Does UML fit in Agile/Scrum environment?” during a UML session presented by myself & one of my colleague at our office CastleRock, Kolkata.
Well the answer is yes, UML is not a methodology dependent you can apply it to any of the software development process. If we have a blueprint of the whole architecture, whenever we are required to make changes or alter a section/ module we can very easily trace which all sections/ modules would get effected & at the same time you can figure out how much time it might take to finish the job.

You can checkout the list of UML tools at http://www.sereferences.com/uml-tools.php.

In the next post I will cover different UML diagrams.