What Is 2-Tier vs 3-Tier Architecture in DBMS?

TL;DR

2-tier architecture has a client layer and a database server, where an interface on the client machine connects through JDBC-ODBC and the server processes the application program directly. 3-tier adds a business layer between client and data layer, so queries are processed there instead. 2-tier wins on maintenance; 3-tier wins on scalability and security.

Transcript

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Key Insights

• Tier simply means layer, so 2-tier architecture means two layers: a client layer and a database server. The client machine runs an interface, or API, that fetches data from the database server.
• The client and the database server are not necessarily wired together and may sit at different locations, so they first make a connection through JDBC-ODBC before any query is sent from the interface to the server.
• In 2-tier, the application program written on the client can be in any language, such as Java. It travels to the database server, which converts it, processes and executes it, and returns the requested data to the client.
• 2-tier architecture is also called client server architecture. A railway reservation counter shows it in action: the clerk enters journey details on a client machine, which calls train and seat availability from the database server and produces the ticket.
• Banking at a physical branch is another 2-tier example. The clerk enters the customer's form details on a client machine, the server holding account details checks whether the requested amount exists, and the response completes the transaction.
• Maintenance is the biggest advantage of 2-tier architecture because clients are limited and authorized, such as bank employees recruited through a particular job, and the databases being accessed are limited too.
• Scalability and security are the two failures of 2-tier architecture. It breaks when users are huge in number, accessing any amount of data 24x7 from any location, and the client interacting directly with the database is a vulnerability.
• 3-tier architecture places a business layer between the client layer and the data layer. The business layer processes queries on a dedicated application server, so the database server never reaches the bottleneck state caused by every client asking it to process queries.

Questions & Answers

Q: What is 2-tier architecture in DBMS?

2-tier architecture means two layers: a client layer and a database server. Tier simply means layer. The client machine runs an interface, or API, that helps fetch data from the database server. Because the client and server are not necessarily wired together and may be at different locations, the API creates a connection through JDBC-ODBC. The user writes a query on the interface, the query travels to the database server as an application program, the server processes and executes it, and the demanded data is returned to the client. It is also called client server architecture.

Q: What is the difference between 2-tier and 3-tier architecture?

2-tier has two layers, the client layer and the database server, and the client interacts directly with the database. 3-tier has three layers: the application or client layer, a business layer, and the database or data layer. In 2-tier the query is processed on the database server itself, which puts it at risk of a bottleneck state when many clients send queries. In 3-tier the business layer processes the queries first and hands the data layer a fully formed request, so load on the database server is reduced. 2-tier is easier to maintain, while 3-tier is better for scalability and security.

Q: Why is 3-tier architecture more secure than 2-tier?

In 2-tier architecture the client interacts directly with the database, and that direct interaction is itself the vulnerability, because a client with direct database access can create a problem. In 3-tier architecture the user is on one side and the data is on the other, with a business layer sitting in the middle so the data is never directly interacted with by the user. The user does not even know where the data actually is. Examples given are Gmail and IRCTC, where you keep your mails or stay logged in without knowing the location of your data.

Q: What does the business layer do in 3-tier architecture?

The business layer works as an intermediator between the client layer and the data layer. The interface on the client can be written in Java, PHP, or many other languages, and the business layer supports those applications. When a user fills checkboxes, buttons, and boxes on an interface such as IRCTC or banking, a query is automatically generated and sent to the business layer as an application program. The business layer processes it, runs all the checks, and converts it into complete low level machine language before passing it to the data layer. It then takes the returned data and formats it back for the same interface the user is using.

Q: Why does 2-tier architecture fail at scale?

2-tier architecture works when clients are limited and authorized, but it fails when the number of users is huge, when users access data 24x7 at any time, from any location, and can access any amount of data. In that setting the database server also has to process every query itself as well as fetch the data, which puts it at risk of entering a bottleneck state. Scalability is the first problem and security is the second, which is why systems have largely shifted to 3-tier architecture, although 2-tier is still used.

Q: What are real life examples of 2-tier architecture?

Indian Railways reservation at a station is one example. When you fill a form at the window, the person sitting on the other side has a client machine where they enter your information and date of journey, then call the train details from the database server to check how many seats are available, process it, and hand you a ticket. Banking at a physical branch is another. When you fill a credit or debit form and give it to the teller or clerk, they enter the information on a client machine that sends it to the server holding your account details, which first checks whether the requested amount is in the account before the transaction completes.

Q: What is the main disadvantage of 3-tier architecture?

Maintenance, which was the biggest advantage of 2-tier architecture, becomes a bit of a problem in 3-tier. The more devices and the more layers you add, the more complex the system becomes, and with three layers the maintenance effort is greater. The tradeoff is accepted today because security and scalability are kept at the high end, and organizations reason that they have enough manpower and enough money to absorb the maintenance cost, while user data must be available 24x7 and must be secure.

Q: How does the database server avoid becoming a bottleneck in 3-tier architecture?

In 2-tier the database server both processes the query and fetches the data, and with lots of clients loading it that way it can enter a bottleneck state. In 3-tier a dedicated application server, the business layer, is placed in the middle and processes the queries of all the users no matter how many there are. It runs the checks and converts the request into machine language, so the database server receives a fully formed request and does not need to process it. The data, which in a relational database is in the form of tables, is simply picked up and returned through the business layer to the user.

Summary & Key Takeaways

• 2-tier architecture, also called client server architecture, consists of two layers: the client layer and the database server. An interface or API runs on the client machine and creates a connection to the database through JDBC-ODBC, since the client and the server are not necessarily directly wired and may sit at different locations.

• In 2-tier, the query written on the interface travels to the database server as an application program, which can be in any high level language such as Java. The server converts it, processes and executes it, then returns the demanded data to the client. Real world examples include railway reservation counters and bank teller machines.

• 3-tier architecture adds a business layer between the application or client layer and the database or data layer. The business layer works as an intermediator: it processes the application program, converts it into low level machine language, and passes a fully formed request to the data layer, removing that processing load from the database server.