A simple version of Reddis-like in-memory database in Java
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SET <VAR> <VALUE>- Stores the variable to the given value
- Runs in O(1) time
- Overrides the value with the new value, if the variable has been set in the same transaction block
- Stores the variable to the given value
-
UNSET <VAR>- Removes the value mapped to the name
- Runs in O(1) time
- Removes the value mapped to the name
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GET <VAR>- Returns the value associated to the variable
- Runs in O(1) time
- If no value has been set or the variable has been previously unset, then returns "NULL"
- Returns the value associated to the variable
-
NUMEQUALTO <VALUE>- Return the number of variables with the same value in the database
- Runs in O(1) time
- Return the number of variables with the same value in the database
Transactions commands:
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BEGIN- Creates a new transaction block
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COMMIT- Closes all the open transaction blocks and commits all the new changes. If no transaction block has been created, it returns "NO TRANSACTION", or if there has been no operations in a block has been made, it returns "NOTHING TO COMMIT" and closes the block
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ROLLBACK- Ignores all the commands in the most recent transaction block.
- Similar to a "revert" to an older version in databases
- If no block has been created, it returns "NO TRANSACTION" or if no operations/commands has been made in the block, it returns "NOTHING TO ROLLBACK TO" and closes the transaction
- Ignores all the commands in the most recent transaction block.
- Compile the code:
- javac SimpleDB.java
- Run it
- java SimpleDB
...
SET A 5
GET A
...
- java SimpleDB