This repo is cloned information that supports the CS186 projects.

• Finding the "latest" version of this project code has been a bit of a game, as it is mostly kept internal to CS186 course members. So I'll be patchworking together sources I can find publicly to support this learning.
• I will store project specifications in a subdirectory as I acquire and complete them from the course gitbook (https://cs186berkeley.net/fa22/ and https://cs186berkeley.net/fa23/).
• If I find I am running ahead of the Jan 2024 course, I will pull project sheets from https://github.com/PKUFlyingPig/CS186/blob/master/project-handout/proj6/getting-started.md.
• I may add further course resources and notes in a subdirectory in the future; currently these are being stored locally.

This repo contains a bare-bones database implementation, which supports executing simple transactions in series. In the assignments of CS186 class, I will cover:

1. SQL use (practice with SQL Lite) - Project 1
2. B+ tree indices - Project 2
3. Efficient join algorithms and Query optimization - Project 3
4. Multigranularity and locking to support concurrent execution of transactions - Project 4
5. Database recovery - Project 5

I've chosen to use JDK 11 with IntelliJ. After cloning this repo, I imported the project as a Maven project (by selecting its pom.xml file.) I then compiled the code and ran the tests, as well as running the CLI application and stepping through it under a debugger.

See IntelliJ setup

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.

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 subdirectory cli/parser contains automatically generated code 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).

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.

The common directory contains bits of useful code and general interfaces that are not limited to any one part of the codebase.

The concurrency directory contains a skeleton for adding multigranularity locking to the database (supports project 4).

Our database has, like most DBMSes, 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:

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.

The index directory contains a skeleton for implementing B+ tree indices (supports Project 2.)

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).

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.

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.

The recovery directory contains a skeleton for implementing database recovery a la ARIES. You will be implementing this in Project 5.

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.

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.

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.

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.

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:

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<Record> 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.