Lock-based protocols in DBMS Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to acquire a shared lock on a data item.

DBMS Theory

lock.acquire([1]);

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AX

BS

CU

DR

Attempts:

3 left

💡 Hint

Common Mistakes

Using exclusive lock 'X' when only reading is needed.

Using undefined lock types like 'R'.

In lock-based protocols, S stands for a shared lock, which allows multiple transactions to read a data item concurrently.

2fill in blank

medium

Complete the code to release a lock on a data item.

DBMS Theory

lock.[1]();

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Await

Bhold

Cacquire

Drelease

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'acquire' instead of 'release' to free a lock.

Using 'wait' which causes the transaction to pause.

The release method frees the lock held on a data item so other transactions can access it.

3fill in blank

hard

Fix the error in the code to check if a lock is compatible with a shared lock.

DBMS Theory

if (lock.type == '[1]') { allowRead(); }

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AS

BX

CU

DN

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing exclusive lock 'X' with shared lock 'S'.

Using undefined lock types like 'N'.

Shared locks (S) are compatible with other shared locks, allowing concurrent reads.

4fill in blank

hard

Fill both blanks to implement strict two-phase locking protocol.

DBMS Theory

beginTransaction();
acquireLock([1]);
// perform operations
[2]();
commitTransaction();

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AX

BreleaseLock

CholdLock

DS

Attempts:

3 left

💡 Hint

Common Mistakes

Releasing locks before commit breaks strict 2PL.

Using shared lock 'S' for write operations.

Strict 2PL requires acquiring an exclusive lock (X) and releasing it only at commit time using releaseLock.

5fill in blank

hard

Fill all three blanks to create a lock table entry for a transaction.

DBMS Theory

lockTable[[1]] = { type: [2], owner: [3] };

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AdataItem

BlockType

CtransactionId

DlockOwner

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing owner with data item.

Using incorrect keys in the lock table.

A lock table entry maps a dataItem to its lockType and the transactionId that owns the lock.