THE SIMPLEDB DATABASE SYSTEM
General Information and Instructions
This document contains the following sections:
* Release Notes
* Server Installation
* Running the Server
* Running Client Programs
* SimpleDB Limitations
* The Organization of the Server Code
I. Release Notes:
This release of the SimpleDB system is Version 3.4, which was
uploaded on March 24, 2021. This release contains fixes a problem with the
file MultibufferProductScan.java from Version 3.3.
SimpleDB is distributed in a WinZip-formatted file. This file contains
five items:
* The folder simpledb, which contains the server-side Java code.
* The folder simpleclient, which contains some client-side code
for a SimpleDB database.
* The folder derbyclient, which contains client-side code
For the Derby database, but with added features not supported
by SimpleDB. These fies are examined in my "Database Design
and Implementation" text.
* The file BookErrata.pdf, which describes how to update the code
in my revised textbook "Database Design and Implementation" so
that it conforms to version 3.4.
* This document.
The author welcomes all comments, including bug reports, suggestions
for improvement, and anecdotal experiences. His email address is
sciore@bc.edu
II. Installation Instructions:
1) Install the Java SDK.
2) To install the SimpleDB engine, you must add the simpledb folder to
your classpath. To do so using Eclipse, first create a new project;
call it ÒSimpleDB EngineÓ. Then from the operating system, copy the
simpledb folder to the src folder of the project. Finally, refresh
the project from Eclipse, using the refresh command in the File menu.
3) The simpleclient folder contains example programs that call the SimpleDB
engine. You should create a new project for them; call it ÒSimpleDB ClientsÓ.
To ensure that the example programs can find the SimpleDB engine code, you
should add the SimpleDB Engine project to the build path of SimpleDB Clients.
Then use the operating system to copy the contents of simpleclient into the
src directory of SimpleDB Clients.
4) The derbyclient folder contains example programs that call the Derby engine.
This code illustrates features of JDBC that SimpleDB does not support, and
is used in Chapter 2 of my "Database Design and Implementation" text.
III. Running the SimpleDB Server:
You run the server code on a host machine, where it will sit and wait for
connections from clients. It is able to handle multiple simultaneous requests
from clients, each on possibly different machines. You can then run a client
program from any machine that is able to connect to the host machine.
To run the SimpleDB server, run Java on the simpledb.server.StartServer class.
The argument to the class is the name of a folder that SimpleDB will use to
hold the database. If you leave out the argument, it will use "studentdb".
If a folder with that name does not exist, then one will be created
automatically in the current directory.
If everything is working correctly, when you run the server with a
new database folder the following will be printed in the server's
window:
creating new database
new transaction: 1
transaction 1 committed
database server ready
If you run the server with an existing database folder, the following
will be printed instead:
recovering existing database
database server ready
In either case, the server will then sit awaiting connections from
clients. As connections arrive, the server will print additional
messages in its window.
The server is implemented using RMI, on port 1099. If a registry is
running when the server is started, it will use that registry;
otherwise, it will create and run the registry itself.
IV. Running Client Code:
SimpleDB clients can be run in embedded mode or network mode. To run a
client in embedded mode, use the EmbeddedDriver JDBC class with the
connection string "jdbc:simpledb:xyz", where xyz is the name of the database.
The database will be created if it does not exist, in the current directory
of the client program. No server is necessary
To run a client in network mode, use the NetworkDriver class with the
connection string "jdbc:simpledb://xyz", where xyz is the name or IP address
of the machine running the SimpleDB server. Note that you cannot specify a
database, because the client must use the database bound to the server.
SimpleDB does not require a username and password, although
it is easy enough to modify the server code to do so.
The following list briefly describes the provided SimpleDB clients.
* CreateStudentDB creates and populates the student database used
by the other clients. It therefore must be the first client run
on a new database.
* StudentMajors prints a table listing the names of students and
their majors.
* FindMajors asks the user for the name of a department. It then
prints the name and graduation year of students having that major.
* SimpleIJ repeatedly prints a prompt asking you to enter a
single line of text containing an SQL statement. The program then
executes that statement. If the statement is a query, the output
table is displayed. If the statement is an update command, then
the number of affected records is printed. If the statement is ill
formed, and error message will be printed. SimpleDB understands
only a limited subset of SQL, which is described below.
* ChangeMajor changes the student named Amy to be a drama major.
It is the only client that updates the database (although you can
use SQLInterpreter to run update commands).
These clients connect to the server at "localhost". If the client is
to be run from a different machine than the server, then its source code
must be modified so that localhost is replaced by the domain name (or IP
address) of the server machine.
V. SimpleDB Limitations
SimpleDB is a teaching tool. It deliberately implements a tiny subset
of SQL and JDBC, and (for simplicity) imposes restrictions not present
in the SQL standard. Here we briefly indicate these restrictions.
SimpleDB SQL
A query in SimpleDB consists only of select-from-where clauses in which
the select clause contains a list of fieldnames (without the AS
keyword), and the from clause contains a list of tablenames (without
range variables).
The where clause is optional. The only Boolean operator is and. The
only comparison operator is equality. Unlike standard SQL, there are
no other comparison operators, no other Boolean operators, no arithmetic
operators or built-in functions, and no parentheses. Consequently,
nested queries, aggregation, and computed values are not supported.
Views can be created, but a view definition can be at most 100
characters.
Because there are no range variables and no renaming, all field names in
a query must be disjoint. And because there are no group by or order by
clauses, grouping and sorting are not supported. Other restrictions:
* The "*" abbreviation in the select clause is not supported.
* There are no null values.
* There are no explicit joins or outer joins in the from clause.
* The union and except keywords are not supported.
* Insert statements take explicit values only, not queries.
* Update statements can have only one assignment in the set clause.
SimpleDB JDBC
SimpleDB implements only the following JDBC methods:
Driver
public Connection connect(String url, Properties prop);
// The method ignores the contents of variable prop.
Connection
public Statement createStatement();
public void close();
Statement
public ResultSet executeQuery(String qry);
public int executeUpdate(String cmd);
ResultSet
public boolean next();
public int getInt();
public String getString();
public void close();
public ResultSetMetaData getMetaData();
ResultSetMetaData
public int getColumnCount();
public String getColumnName(int column);
public int getColumnType(int column);
public int getColumnDisplaySize(int column);
VII. The Organization of the Server Code
SimpleDB is usable without knowing anything about what the code looks
like. However, the entire point of the system is to make the code
easy to read and modify. The basic packages in SimpleDB are structured
hierarchically, in the following order:
* file (Manages OS files as a virtual disk.)
* log (Manages the log.)
* buffer (Manages a buffer pool of pages in memory that acts as a
cache of disk blocks.)
* tx (Implements transactions at the page level. Does locking
and logging.)
* record (Implements fixed-length records inside of pages.)
* metadata (Maintains metadata in the system catalog.)
* query (Implements relational algebra operations. Each operation
has a scan class, which can be composed to create a query tree.)
* parse (Implements the parser.)
* plan (Implements a naive planner for SQL statements.)
* jdbc (Implements embedded and network interfaces for JDBC.)
* server (The place where the startup and initialization code live.
The class Startup contains the main method.)
The basic server is exceptionally inefficient. The following packages
enable more efficient query processing:
* index (Implements static hash and btree indexes, as well as
extensions to the parser and planner to take advantage
of them.)
* materialize (Implements implementations of the relational
operators materialize, sort, groupby, and mergejoin.)
* multibuffer (Implements modifications to the sort and product
operators, in order to make optimum use of available
buffers.)
* opt (Implements a heuristic query optimizer)
My textbook "Database Design and Implementation", recently revised
and published by Springer, describes these packages in considerably
more detail.