Importance of Concurrent scheduling in database

To reduce transaction waiting time and improve throughput we use concurrent scheduling in database. Concurrent means two or more transaction run at a time concurrently. There are two reasons for allowing concurrent scheduling.
(a) Improved throughput and resource utilization: 
We can divide a transaction into many subprogram. Some program related to I/O activity and some are related to CPU activity. When a transaction runs without concurrency, it takes full time to execute and at that time other transaction need to wait to run. But when a transaction run concurrently, some program run in the processor and some run in disks. So the waiting time of other program also decrease and the throughput also increase. Correspondingly the processor and disk utilization also increase. So we can say that concurrent execution improved throughput and resource utilization.
(b) Reduced waiting time:
Concurrent execution reduces the unpredictable delays in running transaction. In the database system there are many transactions running, some are short and some are long. If transactions run serially, a short transaction may have to wait for a preceding long transaction to complete, which can lead to unpredictable delays in running a transaction. To solve this problem database system introduce concurrent scheduling.

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