Question

What are the concurrency-control manager and recovery manager, respectively? What are their purpose?

Answer 1

Before discussing, what are the concurrency-control manager and recovery manager, respectively? What are their purpose?

We should know some of basic terminologies like what is a Transcation, what are ACID properties etc.

A transcation is that smallest unit of work in DMBS that occurs when we perform certain operation on data of relational data bases.

Or we can define a Transaction as a single logical unit of work that accesses and may modifies the contents of a database. Transactions will access and modify the data using read and write operations. In order to maintain integrity in a database, we have to follow certain properties before and after the transaction,these properties are nothing but ACID properties.

In DBMS if multiple transcations are executing concurrently then there is a chance that the data that they are sharing may be gone into an inconsistant state.

So to ensure the integrity or consistency of the data during a transaction we should go for ACID properties:

ACID Properties:

To ensure the integrity or consistency of the data during a transaction,all database systems has to maintain the ACID properties:

• A-Atomicity
• C-Consistency
• I-Isolatoin
• D-Durability

• Atomicity: This property will ensure that either a transaction should be completely executed or should not be executed at all. The transcation should not be executed partially. Let’s take an example of banking system to understand Atomicity more clearly: Suppose there are two persons A and B  Account of person A has a balance of 800$ & that of person B has 900$.Now from Account of person A 200$ are transferring to person B's Account.This is a transaction that will have two operations a) Debiting 200$ from person A’s balance b) Creating 200$ to B’s balance. Let’s say first operation completed successfully while second one got failed in middle due to network error or anything else, in this case A’s balance would be 600$ while B would still having 900$ instead of 1100$. This is a case of inconsistency in a banking system. Either the transaction should complete its execution by performing both the operations or it should not processed either of two operations. The Atomicity property will ensures that.
• Consistency: To preserve the consistency of the database systems, the execution of transaction should be taken place in isolation (that means transactions should run in such a way that if a transcation is already running no other transcation should be running at the same time).
• Isolation: This property ensures that if there are multiple transactions are occuring concurrently then they should not lead the database into an inconsistent state.
• Durability: This property ensures that once a transaction completed successfully, then the changes it has made into the database should be permanentely saved even if there is a system failure. The recovery-management component of database systems ensures the durability of transaction.

Note : If a transcation fullfill the Atomicity, Isolation and Durability propertiy it will automatically ensures the Consistency property!

Now we will discuss what are the concurrency-control manager and recovery manager, respectively? What are their purpose?

Concurrency-control manager:

Concurrency-control manager is a part of DBMS architecture that emforces the concurrency between multiple transcations occuring in a system.

In a multiprogramming environment there are multiple transactions that can be executed simultaneously,so it is highly recommonded to control the concurrency of transactions. So that the data should not be inconsistent and we ensure atomicity, and isolation properties of a transcation.

Purpose of Concurrency-control manager(CCM):

• In a multi user environment to ensures Isolation through mutual exclusion between conflicting transactions
• To smoothly resolve read-write(RW) and write-write(WW) conflict issues
• To control the interaction among the concurrent transactions.
• To ensure serializability between transcations

Recovery manager:

Recovery Manager(RM) is that integral part of DBMS that ensures the Durability property of a transcations.

that is tha main task of RM is to ensures that once a transaction completed successfully, then the changes it has made into the database should be permanentely saved even if there is a system failure.

Apart from this, Recovery Manager(RM) act as a utility that manages the processes by creating backups of all database files and also restoring or recovering files from backups.

Purpose of Recovery-manager(RM):

• As we know that DBMS is a highly complex system having thousands of transactions being executed every second. So the durability and robustness of a DBMS should be the primary concern that can be achived by using a complex architecture having hardware and system software.
• If any transcation fails or crashes then, it is the responsiblity of RM to follow some sort of algorithm or techniques to recover lost data.

Here I have try to exlpain the basic concepts of concurrency-control manager and recovery manager alogn with theri purposes, if you are having any doubts or anything else which is not being understood then please feel

free to ask me in comment section. :)

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