SimpleDB

A simple key/value DB implementation in python / Learning exercise with persistence and write-ahead-logging.

Command Set / API

SET <name> <value>- Set the variable name to the value value. Neither variable names nor values can contain spaces.

GET <name> - Get current value for a variable. Note that the context of the value for the variable is dependent on the transaction scope.

UNSET - Delete the variable and it's value from the database completely.

NUMEQUALTO <value> - Get the current number of variables that are set to value

BEGIN - Start a transaction that will only be written to the database if issued the COMMIT command. Variables within a transaction will shadow their corresponding variables in the parent scope. In the case of an exit or crash, every command that is issued within a BEGIN clause will be persisted to the pending.txt file to be replayed if wanted. Successive transactions are indented to better display the depth.

COMMIT-Save the currently set variables to database. Note that when issuing this command, it will commit the values of the last transaction currently in.

ROLLBACK - Discard current transaction and rollback to previously defined values in the parent transaction.

Display - Shows the currently committed values for all variables

Somewhat Nifty - simple write-ahead-logging

Limitations

• only accepts int type for values
• no concurrency
• limited command set
• lots of other stuffs

Things I tried to do

• All commands persisted to a simple .sdb file
• All commands issued within a transaction persisted to pending.txt
  • Simple write-ahead logging implementation
  • Prompts user to re-load any pending transactions on program crash