gabidavila / inmemory-db

Simple Database Challenge

In the Simple Database problem, you'll implement an in-memory database similar to Redis. For simplicity's sake, instead of dealing with multiple clients and communicating over the network, your program will receive commands via standard input (stdin), and should write appropriate responses to standard output (stdout).

Data Commands

Your database should accept the following commands:

• SET name value – Set the variable name to the value value. Neither variable names nor values will contain spaces.

• GET name – Print out the value of the variable name, or NULL if that variable is not set.

• UNSET name – Unset the variable name, making it just like that variable was never set.

• NUMEQUALTO value – Print out the number of variables that are currently set to value. If no variables equal that value, print 0.

• END – Exit the program. Your program will always receive this as its last command.

Commands will be fed to your program one at a time, with each command on its own line. Any output that your program generates should end with a newline character. Here are some example command sequences:

INPUT	OUTPUT
SET ex 10
GET ex	10
UNSET ex
GET ex	NULL
END

INPUT	OUTPUT
SET a 10
SET b 10
NUMEQUALTO 10	2
NUMEQUALTO 20	0
SET b 30
NUMEQUALTO 10	1
END

inmemory-db's Issues

Flush all values

FLUSH should empty the values in memory.

List Available Keys

Lists all available keys used in memory

Input:
LIST

Return

• name
• address
• a

Update the Readme documentation

New commands were added, keep up to date.

Return sizes

Return the size of the stored items:

• COUNT returns the number of keys used currently
• DBSIZE returns the size of the current storage

INPUT	OUTPUT
COUNT	1000
DBSIZE	0.12B

Add Transactions

Transaction Commands

• BEGIN – Open a new transaction block. Transaction blocks can be nested; a BEGIN can be issued inside of an existing block.

• ROLLBACK – Undo all of the commands issued in the most recent transaction block, and close the block. Print nothing if successful, or print NO TRANSACTION if no transaction is in progress.

• COMMIT – Close all open transaction blocks, permanently applying the changes made in them. Print nothing if successful, or print NO TRANSACTION if no transaction is in progress.

Example:

INPUT	OUTPUT
BEGIN
SET a 10
GET a	10
BEGIN
SET a 20
GET a	20
ROLLBACK
GET a	10
ROLLBACK
GET a	NULL
END

INPUT	OUTPUT
BEGIN
SET a 30
BEGIN
SET a 40
COMMIT
GET a	40
ROLLBACK	NO TRANSACTION
END

INPUT	OUTPUT
SET a 50
BEGIN
GET a	50
SET a 60
BEGIN
UNSET a
GET a	NULL
ROLLBACK
GET a	60
COMMIT
GET a	60
END

INPUT	OUTPUT
SET a 10
BEGIN
NUMEQUALTO 10	1
BEGIN
UNSET a
NUMEQUALTO 10	0
ROLLBACK
NUMEQUALTO 10	1
COMMIT
END

Execute commands from a file

Use a command like EXECUTE file.txt and run all operations there present.