Data compression is a technique that enables you to reduce the disk storage space that a database consumes. Microsoft Azure SQL has the capability to compress data, significantly saving on storage costs and improving the performance of your data queries. In the context of DP-300 exam (Administering Microsoft Azure SQL Solutions), it’s crucial to understand how to configure data compression.
To achieve data compression in Azure SQL Database, you can use two types of Data Compression: ROW and PAGE.
- ROW compression: This method of compression minimizes the space needed to store null and 0 values, alongside reducing the metadata associated with the record.
- PAGE compression: This is an advanced level of compression, which includes both ROW compression and additional prefix and dictionary compression.
How to configure data compression in Azure SQL database
You can configure data compression using T-SQL. Here’s how you can use Table Designer to set up ROW and PAGE compression:
Specify ROW compression for a new table:
SQL
CREATE TABLE Table1
(Col1 int, Col2 nchar(10))
WITH (DATA_COMPRESSION = ROW);
Specify PAGE compression for a new table:
SQL
CREATE TABLE Table2
(Col1 int, Col2 nchar(10))
WITH (DATA_COMPRESSION = PAGE);
For an existing table, you can modify compression using the ALTER TABLE command with the REBUILD option:
SQL
ALTER TABLE Table1
REBUILD PARTITION = ALL
WITH (DATA_COMPRESSION = PAGE);
In the Azure portal, you configure data compression in the ‘Storage settings’ section.
- Go to the Azure portal
- In the left-hand menu, select SQL databases
- Select a database
- In the menu, go to ‘Storage settings’
- Configure the desired compression settings
Please note that the data compression will cause some CPU overhead during the initial compress operation, but the reduced I/O from the smaller size usually outweighs the CPU overhead cost.
Observing the Performance Effects
Once compression is configured, it’s key to monitor the system to observe the impact. Data compression can decrease disk utilization and can boost query performance as data loads into memory more quickly due to reduced I/O operations.
However, data compression may increase CPU utilization because of the additional overhead to compress and decompress data. Utilize available monitoring tools to understand the trade-offs in your specific environment and adjust as necessary.
In conclusion, configuring data compression in Microsoft Azure SQL Database can contribute to significant storage and performance gains. However, it’s crucial to be aware of the associated trade-offs and to monitor the impact of this configuration setting on the overall system. Be sure to review and understand these aspects as part of preparing for the DP-300 (Administering Microsoft Azure SQL Solutions) exam.
Practice Test
True or False: In Microsoft Azure SQL, the ROW and PAGE data compression options allow for reducing the size of tables and indexes.
- True
- False
Answer: True.
Explanation: ROW and PAGE are data compression techniques that you can use to help reduce the disk space that tables and indexes consume and increase the efficiency of I/O operations.
True or False: Data compression in Microsoft Azure SQL is implemented only at the database level.
- True
- False
Answer: False.
Explanation: Data compression in Microsoft Azure SQL can be implemented at the table level and at the index level as well.
Which type of compression is recommended for large scan operations in Microsoft Azure SQL?
- a) ROW Compression
- b) PAGE Compression
- c) COLUMNSTORE Compression
- d) None of the above
Answer: b) PAGE Compression
Explanation: Page compression is suitable for large scan operations as it reduces the amount of I/O required to return the same amount of data.
Which Microsoft Azure SQL configuration allows data storage savings and improves I/O performance for workloads that involve large amounts of data scans?
- a) Disk encryption
- b) Data compression
- c) Hot backup
- d) Load balancing
Answer: b) Data compression
Explanation: Data compression allows saving on data storage and also improves the I/O performance for workloads that involve a large amount of data scans.
True or False: Data compression affects the performance of write operations in Microsoft Azure SQL.
- True
- False
Answer: True.
Explanation: Although data compression reduces space usage and can improve read performance, it might cause some overhead to write operations because of CPU usage to compress or decompress the data.
Which data compression type is generally recommended for fact tables and large dimension tables in warehousing environments?
- a) ROW Compression
- b) PAGE Compression
- c) COLUMNSTORE Compression
- d) None of the above
Answer: c) COLUMNSTORE Compression
Explanation: Columnstore compression is generally recommended for fact tables and large dimension tables in warehousing workloads because it can provide high compression rates and fast query performance for these workloads.
True or False: PAGE Compression provides a higher level of compression than ROW Compression.
- True
- False
Answer: True.
Explanation: PAGE Compression, which includes the benefits of ROW compression, can offer better compression ratios than ROW compression by also compressing redundant data within a page.
True or False: Data compression in Microsoft Azure SQL can only be performed manually.
- True
- False
Answer: False.
Explanation: While data compression can be configured manually, Azure SQL also offers automatic tuning which may automatically compress certain tables in a database.
True or False: Turning on PAGE compression will automatically result in a performance increase.
- True
- False
Answer: False.
Explanation: While PAGE compression can provide disk space benefits, it is not always guaranteed to result in a performance boost — it all depends on workload, system resources and other factors.
What is the primary drawback of using data compression in Microsoft Azure SQL?
- a) Increased disk space
- b) Slower read operations
- c) Increased CPU usage
- d) Slower write operations
Answer: c) Increased CPU usage
Explanation: While data compression can save disk space and potentially improve performance, it does come at a cost: the CPU utilization goes up because it now has to compress and decompress the data.
Interview Questions
What is data compression in Azure SQL Database?
Data compression in Azure SQL Database refers to the process of reducing the storage footprint of data in tables and indexes. It can help save space on storage, reduce I/O, and boost query performance.
What are the types of data compression in Azure SQL Database?
The two types of data compression available in Azure SQL Database are Row-level compression and Page-level compression.
How does row-level compression work in Azure SQL Database?
Row-level compression works by eliminating the unused space in data types and storing fixed character strings in a variable-length format.
How does page-level compression work in Azure SQL Database?
Page-level compression includes the features of row-level compression and also reduces redundant data on a page. It involves three operations: row compression, prefix compression, and dictionary compression.
What is the storage savings of using data compression in Azure SQL Database?
The storage savings from using data compression depends on the type of data. Some data can be compressed by up to 70%, but it’s more typical to see a storage savings of 30-50%.
How do you configure data compression in Azure SQL Database?
Data compression can be configured using the ALTER TABLE or ALTER INDEX Transact-SQL commands with the REBUILD WITH (DATA_COMPRESSION = …) option.
Does Azure SQL Database support dynamic data compression?
Currently, Azure SQL Database does not support dynamic data compression. You have to explicitly set the compression setting for each table and index.
Does data compression in Azure SQL Database affect performance?
Yes, the compression and decompression of data can consume CPU resources, which may affect performance. However, because compressed data is stored in fewer pages, queries may require fewer disk I/O operations, which can improve performance.
How can you estimate the space savings from data compression in Azure SQL Database?
You can estimate the space savings using the sp_estimate_data_compression_savings stored procedure.
Is it possible to compress an already existent table in an Azure SQL Database?
Yes, Existing tables can be compressed by using the ALTER TABLE…REBUILD with the desired DATA_COMPRESSION setting.
What is the command to apply page-level compression to a table in an Azure SQL database?
The command is ALTER TABLE table_name REBUILD PARTITION = ALL WITH (DATA_COMPRESSION = PAGE);
How does Azure SQL Database handle compression for data in memory-optimized tables?
Azure SQL Database uses a different compression technique for data in memory-optimized tables. It uses Columnstore Indexing for compressing data in memory-optimized tables.
Can data compression feature be used in Azure SQL Managed Instance?
Yes, the Data compression feature is available in Azure SQL Managed Instance.
Is there any cost associated with implementing data compression in Azure SQL Database?
While there are no direct costs associated with enabling data compression, the CPU resources used for compressing and decompressing data could lead to increased database DTU (Database Transaction Unit) utilization.
Does Azure SQL Data Warehouses support data compression?
Yes, Azure SQL Data Warehouses use columnar storage which inherently provides a high level of data compression.
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