Overview

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MOOCBase is 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 allow concurrent execution of transactions, and database recovery.

For convenience, the staff will be maintaining a read-only public repo here containing the project skeleton. When starting projects remember to work off of the private repos provided to you through GitHub Classroom rather than the public one.

Code Overview

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 automatically generated automatically from the file MoocParser.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:

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 HeapFile interface is the interface for a heap file that the Table class uses to find pages to write data to.

The PageDirectory class is an implementation of HeapFile 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:

Database db = new Database("database-dir");
try (Transaction t1 = db.beginTransaction()) {
Schema s = new Schema(
Arrays.asList("id", "firstName", "lastName"),
Arrays.asList(Type.intType(), Type.stringType(10), Type.stringType(10))
);
t1.createTable(s, "table1");
t1.insert("table1", Arrays.asList(
new IntDataBox(1),
new StringDataBox("John", 10),
new StringDataBox("Doe", 10)
));
t1.insert("table1", Arrays.asList(
new IntDataBox(2),
new StringDataBox("Jane", 10),
new StringDataBox("Doe", 10)
));
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.