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Shared and exclusive locks

Learn shared vs exclusive locks.

Shared and Exclusive

A shared lock allows reads, an exclusive lock only one operation.

-- Shared: SELECT (okuma kilidi)
-- Exclusive: UPDATE/DELETE (yazma kilidi)

Shared reads, exclusive writes.

Shared and Exclusive — details

Multiple shared locks can coexist. An exclusive lock is alone.

Readers don't block each other, but while one transaction writes (exclusive), others wait to read or change that row.

Practice Shared and Exclusive

Exclusively lock a row with SELECT ... FOR UPDATE.

Starter code

query.sql
-- exclusive lock
SELECT * FROM accounts WHERE id = 1

Sample solution

query.sql
SELECT * FROM accounts WHERE id = 1 FOR UPDATE;

Expected output

id  balance
1   500

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Exclusive

Question 
____ → yazma kilidi
Answer 
Exclusive → yazma kilidi

Explanation: Exclusive is the right answer.

2 How many operations does an exclusive lock allow?

  • Two
  • Unlimited
  • Three
  • One Correct answer

Explanation: An exclusive lock allows only one operation.

3 Shared and exclusive locks: match the terms

Term Meaning
shared read
exclusive write
many shared compatible
one exclusive exclusive

All lessons in Advanced

1 CTE

  1. What is a CTE?
  2. Using WITH
  3. Multiple CTEs
  4. CTE vs subquery
  5. CTE with JOIN
  6. Summary - CTE

2 Recursive CTE

  1. What is a recursive CTE?
  2. Anchor and recursive parts
  3. Walk a hierarchy
  4. Tracking depth
  5. Stopping recursion
  6. Summary - Recursive CTE

3 Window functions

  1. What is a window function?
  2. ROW_NUMBER
  3. RANK and DENSE_RANK
  4. LAG and LEAD
  5. PARTITION BY
  6. Summary - Window functions

4 Project: Analytics report

  1. Analytics design
  2. CTE summary
  3. Top users with ROW_NUMBER
  4. Growth with LAG
  5. Final report

5 Pivot and unpivot

  1. What is pivot?
  2. Pivot with CASE
  3. FILTER clause
  4. Unpivot
  5. Dynamic pivot
  6. Summary - Pivot

6 Materialized view

  1. What is a materialized view?
  2. CREATE
  3. REFRESH
  4. View vs materialized view
  5. Index on materialized views
  6. Summary - Materialized view

7 Stored procedure

  1. What is a procedure?
  2. CREATE PROCEDURE
  3. Parameters
  4. CALL
  5. Control flow
  6. Summary - Stored procedure

8 Function

  1. What is a function?
  2. CREATE FUNCTION
  3. RETURN
  4. Calling a function
  5. Function vs procedure
  6. Summary - Function

9 Trigger

  1. What is a trigger?
  2. BEFORE and AFTER
  3. INSERT trigger
  4. UPDATE trigger
  5. Write an audit trigger
  6. Summary - Trigger

10 Transaction isolation

  1. What is isolation?
  2. READ UNCOMMITTED
  3. READ COMMITTED
  4. REPEATABLE READ
  5. SERIALIZABLE
  6. Summary - Isolation

11 Locking

  1. What is a lock?
  2. Shared and exclusive locks
  3. Deadlock
  4. SELECT FOR UPDATE
  5. Lock timeout
  6. Summary - Locking

12 Query optimization

  1. What is EXPLAIN?
  2. Seq scan vs index scan
  3. Cost
  4. Sargable
  5. N+1 problem
  6. Summary - Optimization

13 Partitioning

  1. What is partitioning?
  2. Range partition
  3. List partition
  4. Hash partition
  5. Partition pruning
  6. Summary - Partitioning

14 Advanced final

  1. Hierarchy report
  2. Window analysis
  3. Procedure and trigger
  4. Optimization