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README 

        
# RookieDB



![The official unofficial mascot of the class projects](images/derpydb-small.jpg)



This repo contains a bare-bones database implementation, which supports

executing simple transactions in series. In the assignments of

this class, you will be adding support for

B+ tree indices, efficient join algorithms, query optimization, multigranularity

locking to support concurrent execution of transactions, and database recovery.



Specs for each of the projects will be released throughout the semester at here: [https://cs186.gitbook.io/project/](https://cs186.gitbook.io/project/)



## Overview



In this document, we explain



- how to fetch the released code

- how to fetch any updates to the released code

- how to setup a local development environment

- how to run tests using IntelliJ

- how to submit your code to turn in assignments

- the general architecture of the released code



## Fetching the released code



For each project, we will provide a GitHub Classroom link. Follow the

link to create a GitHub repository with the starter code for the project you are

working on. Use `git clone` to get a local copy of the newly

created repository.



## Fetching any updates to the released code



In a perfect world, we would never have to update the released code because

it would be perfectly free of bugs. Unfortunately, bugs do surface from time to

time, and you may have to fetch updates. We will provide further instructions

via a post on Piazza whenever fetching updates is necessary.



## Setting up your local development environment



You are free to use any text editor or IDE to complete the assignments, but **we

will build and test your code in a docker container with Maven**.



We recommend setting up a local development environment by installing Java

8 locally (the version our Docker container runs) and using an IDE such as

IntelliJ.



[Java 8 downloads](http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html)



If you have another version of Java installed, it's probably fine to use it, as

long as you do not use any features not in Java 8. You should run tests

somewhat frequently inside the container to make sure that your code works with

our setup.



To import the project into IntelliJ, make sure that you import as a Maven

project (select the pom.xml file when importing). Make sure that you can compile

your code and run tests (it's ok if there are a lot of failed tests - you

haven't begun implementing anything yet!). You should also make sure that you

can run the debugger and step through code.



## Running tests in IntelliJ



If you are using IntelliJ, and wish to run the tests for a given assignment

follow the instructions in the following document:



[IntelliJ setup](intellij-test-setup.md)



## Submitting assignments



To submit a project, navigate to the cloned repo, and use

`git push` to push all of your changes to the remote GitHub repository created

by GitHub Classroom. Then, go to Gradescope class and click on the

project to which you want to submit your code. Select GitHub for the submission

method (if it hasn't been selected already), and select the repository and branch

with the code you want to upload and submit. If you have not done this before,

then you will have to link your GitHub account to Gradescope using the "Connect

to GitHub" button. If you are unable to find the appropriate repository, then you

might need to go to https://github.com/settings/applications, click Gradescope,

and grant access to the `berkeley-cs186-student` organization.



Note that you are only allowed to modify certain files for each assignment, and

changes to other files you are not allowed to modify will be discarded when we

run tests.



## The code



As you will be working with this codebase for the rest of the semester, it is a good idea to get familiar with it. The code is located in the `src/main/java/edu/berkeley/cs186/database` directory, while the tests are located in the `src/test/java/edu/berkeley/cs186/database directory`. The following is a brief overview of each of the major sections of the codebase.



### cli



The cli directory contains all the logic for the database's command line interface. Running the main method of CommandLineInterface.java will create an instance of the database and create a simple text interface that you can send and review the results of queries in. **The inner workings of this section are beyond the scope of the class** (although you're free to look around), you'll just need to know how to run the Command Line Interface.



#### cli/parser



The subdirectory cli/parser contains a lot of scary looking code! Don't be intimidated, this is all generated automatically from the file RookieParser.jjt in the root directory of the repo. The code here handles the logic to convert from user inputted queries (strings) into a tree of nodes representing the query (parse tree).



#### cli/visitor



The subdirectory cli/visitor contains classes that help traverse the trees created from the parser and create objects that the database can work with directly.



### common



The `common` directory contains bits of useful code and general interfaces that

are not limited to any one part of the codebase.



### concurrency



The `concurrency` directory contains a skeleton for adding multigranularity

locking to the database. You will be implementing this in Project 4.



### databox



Our database has, like most DBMS's, a type system distinct from that of the

programming language used to implement the DBMS. (Our DBMS doesn't quite provide

SQL types either, but it's modeled on a simplified version of SQL types).



The `databox` directory contains classes which represents values stored in

a database, as well as their types. The various `DataBox` classes represent

values of certain types, whereas the `Type` class represents types used in the

database.



An example:

```java

DataBox x = new IntDataBox(42); // The integer value '42'.

Type t = Type.intType();        // The type 'int'.

Type xsType = x.type();         // Get x's type, which is Type.intType().

int y = x.getInt();             // Get x's value: 42.

String s = x.getString();       // An exception is thrown, since x is not a string.

```



### index



The `index` directory contains a skeleton for implementing B+ tree indices. You

will be implementing this in Project 2.



### memory



The `memory` directory contains classes for managing the loading of data

into and out of memory (in other words, buffer management).



The `BufferFrame` class represents a single buffer frame (page in the buffer

pool) and supports pinning/unpinning and reading/writing to the buffer frame.

All reads and writes require the frame be pinned (which is often done via the

`requireValidFrame` method, which reloads data from disk if necessary, and then

returns a pinned frame for the page).



The `BufferManager` interface is the public interface for the buffer manager of

our DBMS.



The `BufferManagerImpl` class implements a buffer manager using

a write-back buffer cache with configurable eviction policy. It is responsible

for fetching pages (via the disk space manager) into buffer frames, and returns

Page objects to allow for manipulation of data in memory.



The `Page` class represents a single page. When data in the page is accessed or

modified, it delegates reads/writes to the underlying buffer frame containing

the page.



The `EvictionPolicy` interface defines a few methods that determine how the

buffer manager evicts pages from memory when necessary. Implementations of these

include the `LRUEvictionPolicy` (for LRU) and `ClockEvictionPolicy` (for clock).



### io



The `io` directory contains classes for managing data on-disk (in other words,

disk space management).



The `DiskSpaceManager` interface is the public interface for the disk space

manager of our DBMS.



The `DiskSpaceMangerImpl` class is the implementation of the disk space

manager, which maps groups of pages (partitions) to OS-level files, assigns

each page a virtual page number, and loads/writes these pages from/to disk.



### query



The `query` directory contains classes for managing and manipulating queries.



The various operator classes are query operators (pieces of a query), some of

which you will be implementing in Project 3.



The `QueryPlan` class represents a plan for executing a query (which we will be

covering in more detail later in the semester). It currently executes the query

as given (runs things in logical order, and performs joins in the order given),

but you will be implementing

a query optimizer in Project 3 to run the query in a more efficient manner.



### recovery



The `recovery` directory contains a skeleton for implementing database recovery

a la ARIES. You will be implementing this in Project 5.



### table



The `table` directory contains classes representing entire tables and records.



The `Table` class is, as the name suggests, a table in our database. See the

comments at the top of this class for information on how table data is layed out

on pages.



The `Schema` class represents the _schema_ of a table (a list of column names

and their types).



The `Record` class represents a record of a table (a single row). Records are

made up of multiple DataBoxes (one for each column of the table it belongs to).



The `RecordId` class identifies a single record in a table.



The `PageDirectory` class is an implementation of a heap file that uses a page directory.



#### table/stats



The `table/stats` directory contains classes for keeping track of statistics of

a table. These are used to compare the costs of different query plans, when you

implement query optimization in Project 4.



### Transaction.java



The `Transaction` interface is the _public_ interface of a transaction - it

contains methods that users of the database use to query and manipulate data.



This interface is partially implemented by the `AbstractTransaction` abstract

class, and fully implemented in the `Database.Transaction` inner class.



### TransactionContext.java



The `TransactionContext` interface is the _internal_ interface of a transaction -

it contains methods tied to the current transaction that internal methods

(such as a table record fetch) may utilize.



The current running transaction's transaction context is set at the beginning

of a `Database.Transaction` call (and available through the static

`getCurrentTransaction` method) and unset at the end of the call.



This interface is partially implemented by the `AbstractTransactionContext` abstract

class, and fully implemented in the `Database.TransactionContext` inner class.



### Database.java



The `Database` class represents the entire database. It is the public interface

of our database - users of our database can use it like a Java library.



All work is done in transactions, so to use the database, a user would start

a transaction with `Database#beginTransaction`, then call some of

`Transaction`'s numerous methods to perform selects, inserts, and updates.



For example:

```java

Database db = new Database("database-dir");



try (Transaction t1 = db.beginTransaction()) {

    Schema s = new Schema()

            .add("id", Type.intType())

            .add("firstName", Type.stringType(10))

            .add("lastName", Type.stringType(10));



    t1.createTable(s, "table1");



    t1.insert("table1", 1, "Jane", "Doe");

    t1.insert("table1", 2, "John", "Doe");



    t1.commit();

}



try (Transaction t2 = db.beginTransaction()) {

    // .query("table1") is how you run "SELECT * FROM table1"

    Iterator iter = t2.query("table1").execute();



    System.out.println(iter.next()); // prints [1, John, Doe]

    System.out.println(iter.next()); // prints [2, Jane, Doe]



    t2.commit();

}



db.close();

```



More complex queries can be found in

[`src/test/java/edu/berkeley/cs186/database/TestDatabase.java`](src/test/java/edu/berkeley/cs186/database/TestDatabase.java).