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Concurrency Control Simulation

A web application project to simulate the concurrency controls techniques.

Systems Prerequisites

  • JDK 1.8+
  • Maven
  • Git - Optional in case of download the project

Run the project

  • Download or clone the project
  • cd to pom.xml directory
  • Open the terminal and run mvn jetty:run
  • Open the browser and hit http://localhost:8080

Definitions

Snapshot

It is a picture for the system resources such as disk, buffer, registers, time frame table, logs, lock table, etc at a specific period of time

Disk

It is the data that stored on the physical memory.

Buffer

It is the data that stored on the temporary memory.

Registers

It is the data that stored on the CPU memory.

Time frame Table

It is the table that constructed to order the transactions' operations within a time unit.

Conditions

  • Each transaction id should be unique.
  • No transaction defined without operations.
  • Each transaction should have {@id, @accessTimeUnit} attributes.
  • Each operations should have {@var, @type} attributes.
  • No dashes or spaces allowed in attributes names.
  • All variables should be defined in <disk>...</disk>
  • Allowed mathematical operations are (+, -, /, *)
  • Failures, Start, Commit can be defined as operations.

How to write the system XML?

First you have to define a <snapshot> element.

<?xml version="1.0" encoding="UTF-8"?>
<snapshot>
    ...
</snapshot>

The snapshot contains <disk> and number of <transaction>s

<disk>
    <block id="A">10</block>
    <block id="B">9</block>
</disk>

The disk contains the default values for the variables that used from transactions, it's possible to be shared between transactions.

<transaction id="T1" accessTimeUnit="10">
    <operation var="start"   type="start"/>
    <operation var="A"       type="read"/>
    <operation var="A"       type="sub">50</operation>
    <operation var="A"       type="write"/>
    <operation var="failure" type="failure"/>
    <operation var="B"       type="read"/>
    <operation var="B"       type="add">50</operation>
    <operation var="B"       type="write"/>
    <operation var="commit"  type="commit"/>
</transaction>

The transaction has a set of operations that used to represent operations; for example, a transaction may contain the following operation:

A = A - 50
B = B + 50

Which this can be converted to

Read(A)
A = A - 50
Write(A)
Read(B)
B = B + 50
Write(B)

To be structured as the above xml structure 👆

Important: Make sure every variable in read/write operation has been defined/declared in the disk!

How to execute?

It's simple, you need to 1) fill the XML, 2) select the recovery method and 3) decide to have strict-2PL...

If every thing is OK, you need to hit run ... Enjoy! 😃

Licence

MIT