TempDB Interview Questions & Answers for Azure SQL Database

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Here is a list of real-world, scenario-based interview questions related to TempDB in Azure SQL Database, along with detailed answers.


Basic TempDB Questions

1. What is TempDB in Azure SQL Database?

Answer:
TempDB is a system database in Azure SQL Database that is used for storing temporary objects, intermediate results, and session-related operations such as:
✅ Temporary Tables (#temp, ##global_temp)
✅ Table Variables
✅ Worktables (for sorting, hashing, etc.)
✅ Row Versioning (used in snapshot isolation)
✅ Index Rebuilds and Spools

In Azure SQL Database, TempDB is automatically managed, and users cannot configure its file size manually.


2. How is TempDB different in Azure SQL Database vs. On-Prem SQL Server?

Answer:

FeatureAzure SQL DatabaseSQL Server (On-Premises)
ConfigurationFully managed by AzureManually configurable
File ManagementAuto-resized by AzureUsers define file size
PersistenceResets on each service restartResets on instance restart
Performance ControlHandled internally by AzureUsers optimize tempdb files

3. What happens if TempDB runs out of space in Azure SQL Database?

Answer:
Since TempDB in Azure SQL Database is auto-managed, if it runs out of space:

  • Queries may fail with an out-of-space error.
  • Azure automatically expands TempDB, but there is a limit per service tier.
  • Users can reduce TempDB usage by: ✅ Dropping temporary tables after use.
    ✅ Avoiding large cross joins or spools.
    ✅ Using indexed queries to avoid excessive sorting.

Scenario-Based TempDB Questions

4. A query using a temporary table (#temp) is slow. How would you optimize it?

Answer:
Use Table Variables Instead of #Temp Tables (if suitable)

DECLARE @TempTable TABLE (ID INT PRIMARY KEY, Name NVARCHAR(50));
  • Table variables use less TempDB space than #temp tables.

Use Indexing on Temp Tables

CREATE TABLE #TempTable (
    ID INT PRIMARY KEY CLUSTERED,
    Name NVARCHAR(50)
);
  • Indexing reduces sorting operations in TempDB.

Drop Temporary Tables After Use

DROP TABLE #TempTable;
  • Reduces unnecessary storage usage in TempDB.

5. How do you check TempDB usage in Azure SQL Database?

Answer:
Use DMVs to monitor TempDB usage:

SELECT 
    SUM(allocated_extent_page_count) * 8 / 1024 AS TempDB_MB_Used
FROM sys.dm_db_task_space_usage;
  • This returns TempDB space used (MB) for current sessions.

Check session-level TempDB usage:

SELECT 
    session_id, 
    request_id, 
    database_id, 
    user_objects_alloc_page_count, 
    internal_objects_alloc_page_count 
FROM sys.dm_db_task_space_usage 
WHERE session_id = @@SPID;
  • Identifies TempDB space used per session.

6. How do temporary tables differ from table variables in Azure SQL Database?

Answer:

Feature#Temp TableTable Variable
Stored InTempDBMemory (if small)
ScopeSession-basedBatch-based
Supports Indexes?YesLimited
PerformanceBetter for large datasetsBetter for small datasets
LoggingPartially loggedMinimal logging

Use #TempTable for large datasets with indexes and @TableVariable for small datasets.


7. What are some best practices to reduce TempDB contention?

Answer:
Use Table Variables When Possible (Instead of #Temp Tables)
Avoid SELECT INTO (Prefer INSERT INTO Instead)
Use Indexes to Reduce Sorting
Drop Temporary Objects When No Longer Needed
Minimize Large Cross Joins and Hash Operations


8. How does row versioning impact TempDB in Azure SQL Database?

Answer:
Row Versioning (used in Snapshot Isolation) stores old versions of rows in TempDB, which can increase its size.

To check row versioning usage in TempDB:

SELECT 
    SUM(version_store_reserved_page_count) * 8 / 1024 AS VersionStore_MB
FROM sys.dm_db_file_space_usage;
  • If this value is too high, it indicates TempDB is growing due to versioning.

To reduce TempDB versioning overhead: ✅ Use READ COMMITTED SNAPSHOT OFF if not required.

ALTER DATABASE MyDatabase SET READ_COMMITTED_SNAPSHOT OFF;

✅ Avoid long-running transactions.


9. A report query is running slow due to excessive sorting in TempDB. How do you fix it?

Answer:
1️⃣ Identify Sorting Queries Using TempDB

SELECT 
    session_id, 
    task_alloc_page_count * 8 / 1024 AS TempDB_Usage_MB 
FROM sys.dm_db_task_space_usage
WHERE session_id = @@SPID;

2️⃣ Optimize the Query:

  • Use Indexes to Avoid Sorting
CREATE INDEX idx_ReportDate ON SalesReport(ReportDate);
  • Use Ordered Indexes in JOINs to prevent sorting in TempDB
  • Limit the result set using TOP or LIMIT

10. What happens to TempDB when an Azure SQL Database is restarted?

Answer:

  • TempDB is recreated when the database restarts.
  • All temporary objects (tables, variables) are lost.
  • Statistics and indexes on TempDB objects are reset.
  • The default size of TempDB is restored (based on Azure’s automatic sizing).

11. Can you configure TempDB file size in Azure SQL Database?

Answer:
❌ No, TempDB file size is auto-managed in Azure SQL Database.
However, you can monitor and reduce usage to optimize performance.


12. How do you check the number of TempDB files in Azure SQL Database?

Answer:

SELECT file_id, name, physical_name, size, max_size
FROM sys.master_files
WHERE database_id = DB_ID('tempdb');
  • Unlike SQL Server, Azure SQL manages the number of TempDB files automatically.

13. Why is TempDB contention less of a problem in Azure SQL Database?

Answer:
TempDB is automatically scaled by Azure.
Multiple TempDB files are managed by Azure.
Resources are isolated per database, reducing contention.


Advanced Scenario-Based Questions

14. Your workload suddenly starts consuming excessive TempDB space. How do you troubleshoot it?

Answer:
1️⃣ Check Queries Using TempDB Space:

SELECT session_id, task_alloc_page_count, task_dealloc_page_count 
FROM sys.dm_db_task_space_usage
ORDER BY task_alloc_page_count DESC;

2️⃣ Identify Which Tables Are Using TempDB:

SELECT OBJECT_NAME(object_id), partition_id, index_id
FROM tempdb.sys.partitions;

3️⃣ Check Open Transactions Holding TempDB Space:

DBCC OPENTRAN;

Fix:

  • Kill long-running transactions.
  • Rewrite inefficient queries using TempDB.

15. A query running with snapshot isolation is causing excessive TempDB usage. How do you fix it?

Answer:
1️⃣ Check Row Versioning Usage in TempDB:

SELECT version_store_reserved_page_count * 8 / 1024 AS VersionStore_MB
FROM sys.dm_db_file_space_usage;

2️⃣ Reduce Unnecessary Row Versioning:

  • Disable Snapshot Isolation if not needed
ALTER DATABASE MyDatabase SET ALLOW_SNAPSHOT_ISOLATION OFF;
  • Use explicit COMMIT in transactions to avoid long version chains.

Final Thoughts

TempDB in Azure SQL Database is crucial for query performance, sorting, and temporary storage. Understanding troubleshooting techniques, performance optimizations, and monitoring tools is essential for handling real-world database issues.

🚀 Do you need hands-on scripts for TempDB troubleshooting? Let me know!

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