Serializability in DBMS

The backbone of the most modern application is the form of DBMS. When we design the form properly, then it provides high-performance and relative storage solutions to our application. In this topic, we are going to explain the serializability concept and how this concept affects the DBMS deeply. We also understand the concept of serializability with some examples. Finally, we will conclude this topic with an example of the importance of serializability.

What is Serializability in DBMS?

In the field of computer science, serializability is a term that is a property of the system that describes how the different process operates the shared data. If the result given by the system is similar to the operation performed by the system, then in this situation, we call that system serializable. Here the cooperation of the system means there is no overlapping in the execution of the data. In DBMS, when the data is being written or read then, the DBMS can stop all the other processes from accessing the data.

In the MongoDB developer certificate, the DBMS uses various locking systems to allow the other processes while maintaining the integrity of the data. In MongoDB, the most restricted level for serializability is the employee can be restricted by two-phase locking or 2PL. In the first phase of the locking level, the data objects are locked before the execution of the operation. When the transaction has been accomplished, then the lock for the data object is released. This process guarantees that there is no conflict in operation and that all the transaction views the database as a conflict database.

The two-phase locking or 2PL system provides a strong guarantee for the conflict of the database.

It can reduce the decreased performance and then increase the overhead acquiring capacity and then release the lock of the data. As a result, the system allows the constraint serializability for better performance of the DBMS. This ensures that the final result is the same as some sequential execution and performs the improvement of the operation that is involved in the database.

Thus, serializability is the system's property that describes how the different process operates the shared data. In DBMS, the overall Serializable property is adopted by locking the data during the execution of other processes. Also, serializability ensures that the final result is equivalent to the sequential operation of the data.

What is a Serializable Schedule?

• In DBMS, the Serializable schedule is a property in which the read and write operation sequence does not disturb the serializability property. This property ensures that the transaction is executed automatically with the other transaction. In DBMS, the order of the serializability must be the same as some serial schedules of the same transaction.
• In DBMS, there are several algorithms available to check the serializability of the database. One of the most important algorithms is the conflict serializability algorithm. The conflict serializability algorithm is the ability to check the potential of the conflict in the database. When the two transactions access the same data, this conflict occurs in the database. If there is no conflict, then there is guaranteed serializability in the database. However, if there is a conflict occurs, then there is a chance of serializability.
• Another algorithm that is used to check the serializability of the database is the DBMS algorithm. With the help of the DBMS algorithm, we can check the potential mutual dependencies between two transactions. When the two transactions give the correct output, then mutual dependencies exist. When there are no mutual dependencies, then there is a guaranteed serializable in the database. However, if there are mutual dependencies, then there will be a chance of serializable.
• We can also check the serializability of the database by using the precedence graph algorithm. A precedence relationship exists when one transaction must precede another transaction for the schedule to be valid. If there are no cycles, then the serializability of schedules in DBMS is guaranteed. However, if there are cycles, the schedule may or may not be serializable. To understand different algorithms comprehensively, take the MongoDB Administration certification and get expert analysis on the concept of serializability in DBMS.

Types of Serializability

In DBMS, all the transaction should be arranged in a particular order, even if all the transaction is concurrent. If all the transaction is not serializable, then it produces the incorrect result.

In DBMS, there are different types of serializable. Each type of serializable has some advantages and disadvantages. The two most common types of serializable are view serializability and conflict serializability.

1. Conflict Serializability

Conflict serializability is a type of conflict operation in serializability that operates the same data item that should be executed in a particular order and maintains the consistency of the database. In DBMS, each transaction has some unique value, and every transaction of the database is based on that unique value of the database.

This unique value ensures that no two operations having the same conflict value are executed concurrently. For example, let's consider two examples, i.e., the order table and the customer table. One customer can have multiple orders, but each order only belongs to one customer. There is some condition for the conflict serializability of the database. These are as below.

• Both operations should have different transactions.
• Both transactions should have the same data item.
• There should be at least one write operation between the two operations.

If there are two transactions that are executed concurrently, one operation has to add the transaction of the first customer, and another operation has added by the second operation. This process ensures that there would be no inconsistency in the database.

2. View Serializability

View serializability is a type of operation in the serializable in which each transaction should produce some result and these results are the output of proper sequential execution of the data item. Unlike conflict serialized, the view serializability focuses on preventing inconsistency in the database. In DBMS, the view serializability provides the user to view the database in a conflicting way.

In DBMS, we should understand schedules S1 and S2 to understand view serializability better. These two schedules should be created with the help of two transactions T1 and T2. To maintain the equivalent of the transaction each schedule has to obey the three transactions. These three conditions are as follows.

• The first condition is each schedule has the same type of transaction. The meaning of this condition is that both schedules S1 and S2 must not have the same type of set of transactions. If one schedule has committed the transaction but does not match the transaction of another schedule, then the schedule is not equivalent to each other.
• The second condition is that both schedules should not have the same type of read or write operation. On the other hand, if schedule S1 has two write operations while schedule S2 has one write operation, we say that both schedules are not equivalent to each other. We may also say that there is no problem if the number of the read operation is different, but there must be the same number of the write operation in both schedules.
• The final and last condition is that both schedules should not have the same conflict. Order of execution of the same data item. For example, suppose the transaction of schedule S1 is T1, and the transaction of schedule S2 is T2. The transaction T1 writes the data item A, and the transaction T2 also writes the data item A. in this case, the schedule is not equivalent to each other. But if the schedule has the same number of each write operation in the data item then we called the schedule equivalent to each other.

Testing of Serializability in DBMS with Examples

Serializability is a type of property of DBMS in which each transaction is executed independently and automatically, even though these transactions are executed concurrently. In other words, we can say that if there are several transactions executed concurrently, then the main work of the serializability function is to arrange these several transactions in a sequential manner.

For better understanding, let's explain these with an example. Suppose there are two users Sona and Archita. Each executes two transactions. Let's transactions T1 and T2 are executed by Sona, and T3 and T4 are executed by Archita. Suppose transaction T1 reads and writes the data item A, transaction T2 reads the data item B, transaction T3 reads and writes the data item C and transaction T4 reads the data item D. Lets the schedule the above transaction as below.

Let's first discuss why these transactions are not serializable.

In order for a schedule to be considered serializable, it must first satisfy the conflict serializability property. In our example schedule above, notice that Transaction 1 (T1) and Transaction 2 (T2) read data item B before either writing it. This causes a conflict between T1 and T2 because they are both trying to read and write the same data item concurrently. Therefore, the given schedule does not conflict with serializability.

However, there is another type of serializability called view serializability which our example does satisfy. View serializability requires that if two transactions cannot see each other's updates (i.e., one transaction cannot see the effects of another concurrent transaction), the schedule is considered to view serializable. In our example, Transaction 2 (T2) cannot see any updates made by Transaction 4 (T4) because they do not share common data items. Therefore, the schedule is viewed as serializable.

It's important to note that conflict serializability is a stronger property than view serializability because it requires that all potential conflicts be resolved before any updates are made (i.e., each transaction must either read or write each data item before any other transaction can write it). View serializability only requires that if two transactions cannot see each other's updates, then the schedule is view serializable & it doesn't matter whether or not there are potential conflicts between them.

All in all, both properties are necessary for ensuring correctness in concurrent transactions in a database management system.

Benefits of Serializability in DBMS

Below are the benefits of using the serializable in the database.

1. Predictable execution: In serializable, all the threads of the DBMS are executed at one time. There are no such surprises in the DBMS. In DBMS, all the variables are updated as expected, and there is no data loss or corruption.
2. Easier to Reason about & Debug: In DBMS all the threads are executed alone, so it is very easier to know about each thread of the database. This can make the debugging process very easy. So we don't have to worry about the concurrent process.
3. Reduced Costs: With the help of serializable property, we can reduce the cost of the hardware that is being used for the smooth operation of the database. It can also reduce the development cost of the software.
4. Increased Performance:In some cases, serializable executions can perform better than their non-serializable counterparts since they allow the developer to optimize their code for performance.

Conclusion

DBMS transactions must follow the ACID properties to be considered serializable. There are different types of serializability in DBMS, each with its own benefits and drawbacks. In most cases, selecting the right type of serializability will come down to a trade-off between performance and correctness.

Selecting the wrong type of serializability can lead to errors in your database that can be difficult to debug and fix. Hopefully, this guide has given you a better understanding of how Serializability in DBMS works and what kinds of serializability exist.