CRUD operations in HBase in Hadoop - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this HBase shell command?

Consider the following HBase shell commands executed sequentially:

create 'students', 'info'
put 'students', 'row1', 'info:name', 'Alice'
put 'students', 'row1', 'info:age', '21'
get 'students', 'row1', 'info:name'

What will be the output of the get command?

Hadoop

create 'students', 'info'
put 'students', 'row1', 'info:name', 'Alice'
put 'students', 'row1', 'info:age', '21'
get 'students', 'row1', 'info:name'

A

COLUMN              CELL
 info:age            timestamp=..., value=21

B

COLUMN              CELL
 info:age            timestamp=..., value=Alice

C

COLUMN              CELL
 info:name           timestamp=..., value=21

D

COLUMN              CELL
 info:name           timestamp=..., value=Alice

💡 Hint

The get command retrieves the value of the specified column for the given row.

The get command fetches the value stored in the 'info:name' column for 'row1', which is 'Alice'.

❓ data_output

intermediate

How many rows remain after this delete operation?

Given a table 'employees' with rows 'emp1', 'emp2', and 'emp3', after running:

deleteall 'employees', 'emp2'

How many rows will remain in the table?

Hadoop

deleteall 'employees', 'emp2'

A 2

B 3

C 1

D 0

💡 Hint

The deleteall command removes all columns for the specified row.

Deleting all columns of 'emp2' removes that row, so only 'emp1' and 'emp3' remain.

🔧 Debug

advanced

Identify the error in this HBase shell command sequence

What error will occur when running this sequence?

create 'products', 'details'
put 'products', 'p1', 'details:name', 'Laptop'
put 'products', 'p1', 'details:price', 1200
get 'products', 'p1', 'details:price'

Hadoop

create 'products', 'details'
put 'products', 'p1', 'details:name', 'Laptop'
put 'products', 'p1', 'details:price', 1200
get 'products', 'p1', 'details:price'

A TypeError because 1200 is not a string

B No error; output shows price as '1200'

C SyntaxError due to missing quotes around 1200

D NullPointerException because 'products' table does not exist

💡 Hint

HBase shell converts numbers to strings automatically in put.

HBase shell treats all values as strings, so 1200 is stored as '1200' without error.

🚀 Application

advanced

Which command updates a cell value in HBase?

You want to change the value of the cell in row 'r1', column 'info:status' to 'active' in the 'users' table. Which command will do this?

A modify 'users', 'r1', 'info:status', 'active'

B update 'users', 'r1', 'info:status', 'active'

C put 'users', 'r1', 'info:status', 'active'

D set 'users', 'r1', 'info:status', 'active'

💡 Hint

HBase uses put to insert or update data.

The put command inserts or updates the value of a cell in HBase.

🧠 Conceptual

expert

What happens if you try to get a non-existent row in HBase?

If you run get 'orders', 'order999' but 'order999' does not exist in the 'orders' table, what will be the result?

Hadoop

get 'orders', 'order999'

A Returns an empty result with no columns

B Raises a KeyError exception

C Returns the last row in the table

D Returns null and stops the shell

💡 Hint

HBase returns empty results for missing rows instead of errors.

If the row does not exist, HBase returns an empty result without error.

Practice

1. Which HBase operation is used to retrieve data from a table?

easy

A. Get

B. Put

C. Delete

D. Scan

Solution

1. Step 1: Understand HBase CRUD operations

   HBase uses Get to read data, Put to create or update, Delete to remove, and Scan to read multiple rows.

2. Step 2: Identify the read operation

   Get is the specific operation to retrieve data for a single row.

3. Final Answer:

   Get -> Option A

4. Quick Check:

   Read = Get [OK]

Hint: Remember: Get = Read, Put = Create/Update [OK]

Common Mistakes:

• Confusing Put with Get
• Using Delete to read data
• Thinking Scan is for single row read

2. Which of the following is the correct syntax to insert data into HBase using Java API?

easy

A. Delete delete = new Delete(Bytes.toBytes("row1")); table.put(delete);

B. Get get = new Get(Bytes.toBytes("row1")); table.put(get);

C. Put put = new Put(Bytes.toBytes("row1")); put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("qual"), Bytes.toBytes("value")); table.put(put);

D. Put put = new Put("row1"); put.add("cf", "qual", "value"); table.get(put);

Solution

1. Step 1: Review correct Put syntax in HBase Java API

   Put requires a row key as bytes, then addColumn with column family, qualifier, and value as bytes, then call table.put(put).

2. Step 2: Check each option

   Put put = new Put(Bytes.toBytes("row1")); put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("qual"), Bytes.toBytes("value")); table.put(put); matches correct syntax. Get get = new Get(Bytes.toBytes("row1")); table.put(get); wrongly uses Get with put. Delete delete = new Delete(Bytes.toBytes("row1")); table.put(delete); uses Delete with put. Put put = new Put("row1"); put.add("cf", "qual", "value"); table.get(put); uses wrong constructors and methods.

3. Final Answer:

   Put put = new Put(Bytes.toBytes("row1")); put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("qual"), Bytes.toBytes("value")); table.put(put); -> Option C

4. Quick Check:

   Put syntax correct = Put put = new Put(Bytes.toBytes("row1")); put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("qual"), Bytes.toBytes("value")); table.put(put); [OK]

Hint: Put needs Bytes.toBytes for all keys and values [OK]

Common Mistakes:

• Using Get or Delete with put()
• Not converting strings to bytes
• Wrong method names like add() instead of addColumn()

3. What will be the output of the following HBase Java code snippet?

Put put = new Put(Bytes.toBytes("row1"));
put.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("name"), Bytes.toBytes("Alice"));
table.put(put);

Get get = new Get(Bytes.toBytes("row1"));
Result result = table.get(get);
byte[] value = result.getValue(Bytes.toBytes("cf"), Bytes.toBytes("name"));
System.out.println(Bytes.toString(value));

medium

A. Compilation Error

B. null

C. cf:name

D. Alice

Solution

1. Step 1: Insert data with Put operation

   The code puts value "Alice" in column family "cf" and qualifier "name" for row "row1".

2. Step 2: Retrieve data with Get operation

   The Get fetches the row "row1" and extracts the value for "cf:name" which is "Alice".

3. Final Answer:

   Alice -> Option D

4. Quick Check:

   Put then Get returns inserted value [OK]

Hint: Put then Get returns inserted value exactly [OK]

Common Mistakes:

• Expecting null if not flushed
• Confusing column family and qualifier
• Forgetting to convert bytes to string

4. Identify the error in the following HBase delete operation code snippet:

Delete delete = new Delete("row1");
delete.addColumn(Bytes.toBytes("cf"), Bytes.toBytes("qual"));
table.delete(delete);

medium

A. Delete constructor argument should be bytes, not string

B. addColumn method is deprecated, should use addColumns

C. table.delete() method does not exist

D. No error, code is correct

Solution

1. Step 1: Check Delete constructor parameter type

   The Delete constructor requires a byte array for the row key, not a plain string.

2. Step 2: Verify method usage

   addColumn is valid for deleting a specific column. table.delete() is correct method.

3. Final Answer:

   Delete constructor argument should be bytes, not string -> Option A

4. Quick Check:

   Delete row key must be bytes [OK]

Hint: Always convert row keys to bytes in HBase operations [OK]

Common Mistakes:

• Passing string directly instead of bytes
• Confusing addColumn with addColumns
• Thinking table.delete() is invalid

5. You want to update the value of a column "status" in column family "info" for row "user123" in HBase. Which sequence of operations is correct to ensure the update is saved and can be read back immediately?

hard

A. Create a Delete for the old value, call table.delete(delete), then create a Put with new value and call table.put(put)

B. Create a Put with new value, call table.put(put), then call table.get(get) to read updated value

C. Call table.get(get) first, then create a Put with new value and call table.put(put)

D. Create a Put with new value, call table.get(get), then call table.put(put)

Solution

1. Step 1: Use Put to update the column value

   In HBase, Put operation overwrites existing values for the same column, so create a Put with the new "status" value for "user123".

2. Step 2: Save and verify update

   Call table.put(put) to save the update, then use table.get(get) to read back the updated value immediately.

3. Final Answer:

   Create a Put with new value, call table.put(put), then call table.get(get) to read updated value -> Option B

4. Quick Check:

   Put updates value, Get reads updated value [OK]

Hint: Put overwrites; Get reads latest value after put [OK]

Common Mistakes:

• Deleting before putting is unnecessary
• Getting before putting returns old value
• Calling get before put misses update