Task $3(2$ marks$)$

Processing database transactions at READ COMMITTED isolation level

This task applies to a sample database created in Assignment $2.$

Consider the following SQL script.Assume that the script listed above is processed as a database transaction T at READ COMMITTED isolation level.$(1)(1$ mark$)$

Show a sample concurrent execution of a database transaction $T$ together with another database transaction also running at READ COMMITTED isolation level, such that the execution ends up in deadlock.

When visualizing a concurrent execution use a technique of two$-$dimensional diagrams presented to you during the lecture classes, for example, see a presentation $14$ Transaction Processing in PostgreSQL slide $8.$

$(2)$

Explain all details on why a concurrent execution of a transaction T or another database transaction also running at READ COMMITTED isolation level ends up in a deadlock.

$(3)(1$ mark$)$

Show how a transaction T must be modified to avoid a deadlock. A modified transaction still must be processed at READ COMMITTED level. Write a new version of a transaction T$.$