To compress all tables in an Oracle database, you can use the "ALTER TABLE" command with the "COMPRESS" clause. This command can be used to compress tables and their associated indexes. It is important to note that table compression is a resource-intensive operation and can have an impact on performance, so it is recommended to analyze the performance implications before proceeding with compression. Additionally, you may want to backup your database before compressing tables to avoid data loss in case of any unexpected issues during the compression process.
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How to use the COMPRESS keyword in Oracle for table compression
To use the COMPRESS keyword in Oracle for table compression, you can add it to the CREATE TABLE statement or use the ALTER TABLE statement to compress an existing table. Here is the syntax for using the COMPRESS keyword:
- For creating a new table with compression:
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CREATE TABLE table_name ( column1 datatype [NULL | NOT NULL], column2 datatype [NULL | NOT NULL], ... ) COMPRESS FOR ALL OPERATIONS; |
This will create a new table with compression enabled for all operations.
- For altering an existing table to compress it:
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ALTER TABLE table_name COMPRESS FOR ALL OPERATIONS;
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This will compress an existing table for all operations.
You can also specify individual columns to be compressed by using the COMPRESS keyword for those columns in the CREATE TABLE or ALTER TABLE statement.
Keep in mind that table compression may have a performance impact, so you should test it thoroughly before implementing it in a production environment.
What is the storage savings achieved by compressing tables in Oracle?
The storage savings achieved by compressing tables in Oracle can vary depending on factors such as the type of compression used, the data being compressed, and the size of the table.
In general, compression can reduce the storage footprint of a table by up to 50-80% or even more in some cases. This means that a table that occupies 1 GB of storage space without compression may only take up 200-500 MB of space after compression.
It's worth noting that compression can have a significant impact on storage savings, but it can also impact performance as compressed data needs to be decompressed before it can be used. It's important to consider these trade-offs and test the impact of compression on your specific use case before implementing it in a production environment.
What is the recommended compression strategy for a large Oracle database?
The recommended compression strategy for a large Oracle database is to use Oracle Advanced Compression. This feature allows for efficient compression of data, reducing storage requirements and improving performance. Additionally, it provides various compression options such as table compression, partition compression, and advanced compression for backup and data transport.
Some best practices for using Oracle Advanced Compression include:
- Evaluate and analyze the database to identify the tables and partitions that can benefit from compression.
- Use different compression techniques based on the type of data, such as OLTP data, historical data, or archive data.
- Monitor the performance impact of compression on the database and make adjustments as needed.
- Regularly maintain and reevaluate the compression strategy to ensure optimal performance and storage efficiency.
Overall, Oracle Advanced Compression is a powerful tool that can significantly reduce the storage footprint of a large Oracle database while maintaining performance and scalability.
How to retrieve metadata information about compressed tables in Oracle
To retrieve metadata information about compressed tables in Oracle, you can use the following query:
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SELECT table_name, compression, compress_for FROM user_tables WHERE compression IS NOT NULL;
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This query will return the table name, compression type, and compression algorithm used for all tables in the current user's schema that have compression enabled.
Alternatively, you can use the DBMS_METADATA package to retrieve metadata information about a specific compressed table. Here's an example:
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SELECT DBMS_METADATA.GET_DDL('TABLE', 'TABLE_NAME') FROM dual;
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Replace 'TABLE_NAME' with the name of the compressed table you want to retrieve metadata information for. This query will return the DDL (Data Definition Language) statement for the specified table, which includes information about compression settings.
