Oracle 19c Important Parameters for Performance

Oracle Database 19c is a powerful and scalable database platform that can be used to support a wide variety of workloads. However, in order to achieve optimal performance, it is important to configure the database properly. One way to do this is to set the appropriate initialization parameters.

The following are some of the most important Oracle 19c initialization parameters for performance:

• DB_CACHE_SIZE: This parameter specifies the size of the database cache. The database cache is used to store frequently accessed data and indexes. Increasing the size of the database cache can improve performance by reducing the number of times that the database has to access disk.

The following are some things to keep in mind when setting the value of the DB_CACHE_SIZE parameter:

• The value of the DB_CACHE_SIZE parameter should be large enough to store all of the data and indexes that are frequently accessed by your application.
• The value of the DB_CACHE_SIZE parameter should not be so large that it causes your database to run out of memory.
• You can use the DB_CACHE_ADVISE procedure to determine the optimal value for the DB_CACHE_SIZE parameter.

The following is an example of how to set the DB_CACHE_SIZE parameter in init.ora:

DB_CACHE_SIZE=16G

This will set the size of the database cache to 16 GB.

After you have set the DB_CACHE_SIZE parameter, you need to restart the database for the changes to take effect.

Here are some additional tips for setting up DB_CACHE_SIZE:

• If you are using Automatic Memory Management (AMM), you can let Oracle automatically manage the size of the database cache.
• If you are not using AMM, you can use the DB_CACHE_ADVISE procedure to determine the optimal size for the database cache.
• You can use the V$DB_CACHE_ADVICE view to see the current size of the database cache and the optimal size for the database cache.

By following these tips, you can ensure that your Oracle 19c database has the optimal amount of memory for caching data and indexes. This can improve the performance of your database by reducing the number of times that the database has to access disk.

• SORT_AREA_SIZE: This parameter specifies the size of the sort area. The sort area is used to store data during sorting operations. Increasing the size of the sort area can improve performance by reducing the number of times that the database has to swap data to disk.

he SORT_AREA_SIZE parameter specifies the maximum amount of memory that Oracle will use for a sort. The default value is 2MB. You can increase this value to improve the performance of queries that involve large sorts.

To set the SORT_AREA_SIZE parameter, you can use the ALTER SESSION statement. For example, the following statement sets the SORT_AREA_SIZE parameter to 16MB:

ALTER SESSION SET sort_area_size=16M;

You can also set the SORT_AREA_SIZE parameter in the database initialization file (init.ora). For example, the following entry in init.ora sets the SORT_AREA_SIZE parameter to 32MB:

SORT_AREA_SIZE=32M

Note that the SORT_AREA_SIZE parameter is only effective for queries that are executed in the current session. If you want to make the SORT_AREA_SIZE parameter persistent, you can set it in the database initialization file (init.ora).

Increasing the SORT_AREA_SIZE parameter can improve the performance of queries that involve large sorts. However, it is important to note that increasing the SORT_AREA_SIZE parameter can also increase the amount of memory that is used by the database. Therefore, you should only increase the SORT_AREA_SIZE parameter if you have enough memory available.

Here are some tips for setting the SORT_AREA_SIZE parameter:

• Start with the default value and monitor the performance of your queries.
• If you find that queries that involve large sorts are slow, increase the SORT_AREA_SIZE parameter in small increments.
• Be sure to monitor the memory usage of the database after increasing the SORT_AREA_SIZE parameter.
• Do not increase the SORT_AREA_SIZE parameter beyond the amount of memory that is available on the server.

• HASH_AREA_SIZE: This parameter specifies the size of the hash area. The hash area is used to store data during hashing operations. Increasing the size of the hash area can improve performance by reducing the number of times that the database has to swap data to disk.

The HASH_AREA_SIZE parameter specifies the maximum amount of memory, in bytes, to be used for hash joins. The default value for this parameter is 256MB. You can increase the value of this parameter if you are experiencing performance problems with hash joins.

To set the HASH_AREA_SIZE parameter, you can use the following steps:

1. Open the database configuration file (usually called init.ora).
2. Locate the HASH_AREA_SIZE parameter.
3. Increase the value of the parameter to a value that you think will improve performance.
4. Save the database configuration file.
5. Restart the database.

Once you have restarted the database, the new value of the HASH_AREA_SIZE parameter will be in effect.

Here is an example of how to set the HASH_AREA_SIZE parameter:

HASH_AREA_SIZE=512M

This will set the maximum amount of memory that can be used for hash joins to 512MB.

You can also set the HASH_AREA_SIZE parameter for a specific session using the ALTER SESSION statement. For example, the following statement will set the HASH_AREA_SIZE for the current session to 256MB:

ALTER SESSION SET HASH_AREA_SIZE=256M;

The HASH_AREA_SIZE parameter is a session-specific parameter, so the value that you set for this parameter will only apply to the current session.

If you are experiencing performance problems with hash joins, you can try increasing the value of the HASH_AREA_SIZE parameter. However, you should be careful not to increase the value too much, as this could lead to memory exhaustion.

You can monitor the performance of hash joins using the V$SQL_PLAN view. The HASH_AREA_SIZE column in this view shows the amount of memory that was used for the hash join.

If you are still experiencing performance problems with hash joins after increasing the value of the HASH_AREA_SIZE parameter, you may need to consider other options, such as optimizing your SQL queries or using a different join algorithm.

• PGA_AGGREGATE_LIMIT: This parameter specifies the maximum amount of memory that can be used by the Program Global Area (PGA). The PGA is used to store data and control structures for each user session. Increasing the size of the PGA can improve performance by reducing the number of times that the database has to swap data to disk.

The PGA_AGGREGATE_LIMIT parameter specifies the maximum amount of memory that can be used by the Program Global Area (PGA). The PGA is used to store data and control structures for each user session.

To set the PGA_AGGREGATE_LIMIT parameter in Oracle 19c, you can use the following steps:

1. Open the database configuration file, usually called init.ora.
2. Locate the PGA_AGGREGATE_LIMIT parameter.
3. Set the value of the PGA_AGGREGATE_LIMIT parameter to the desired amount of memory.
4. Save the database configuration file.
5. Restart the database.

The following is an example of how to set the PGA_AGGREGATE_LIMIT parameter in Oracle 19c:

PGA_AGGREGATE_LIMIT=4G

This setting will limit the total amount of memory that can be used by the PGA to 4GB.

It is important to note that the PGA_AGGREGATE_LIMIT parameter is a global setting. This means that it applies to all user sessions. If you need to set different limits for different user sessions, you can use the PGA_AGGREGATE_TARGET parameter. The PGA_AGGREGATE_TARGET parameter allows you to set a per-session limit on the amount of memory that can be used by the PGA.

Here are some additional things to keep in mind when setting the PGA_AGGREGATE_LIMIT parameter:

• The default value of the PGA_AGGREGATE_LIMIT parameter is 0, which means that there is no limit on the amount of memory that can be used by the PGA.
• The PGA_AGGREGATE_LIMIT parameter should be set to a value that is large enough to accommodate the demands of your workload.
• If you set the PGA_AGGREGATE_LIMIT parameter too low, you may experience performance problems.
• If you set the PGA_AGGREGATE_LIMIT parameter too high, you may waste memory.

The best way to determine the optimal value for the PGA_AGGREGATE_LIMIT parameter is to experiment and monitor your database performance.

• SGA_SIZE: This parameter specifies the size of the System Global Area (SGA). The SGA is a shared memory area that contains data and control structures used by the database. Increasing the size of the SGA can improve performance by reducing the number of times that the database has to access disk.

To set up SGA_SIZE in Oracle 19c, you can use the following steps:

1. Open the Oracle Database 19c configuration file. The default location of the configuration file is $ORACLE_HOME/dbs/init.ora.
2. Locate the SGA_SIZE parameter. The SGA_SIZE parameter is typically located near the top of the configuration file.
3. Specify the desired size of the SGA. The SGA_SIZE parameter is specified in bytes. For example, to set the SGA size to 1GB, you would specify the following value:

SGA_SIZE = 1073741824

4. Save the configuration file.
5. Restart the Oracle Database 19c instance.

Once you have set the SGA_SIZE parameter, Oracle Database 19c will allocate the specified amount of memory to the SGA. The SGA is used to store data and control structures used by the database. By increasing the size of the SGA, you can improve the performance of your Oracle Database 19c instance by reducing the number of times that the database has to access disk.

Here are some additional tips for setting the SGA_SIZE parameter:

• The optimal size of the SGA will vary depending on the size and workload of your database.
• You can use the Oracle Database 19c sizing tool to help you determine the optimal size of the SGA.
• You can also use the Oracle Database 19c monitoring tools to track the SGA usage and make adjustments to the SGA size as needed.

By following these tips, you can ensure that the SGA size is properly configured for your Oracle Database 19c instance.

In addition to setting the appropriate initialization parameters, there are other things that you can do to improve the performance of your Oracle 19c database. These include:

• Optimizing your SQL queries
• Compressing your data
• Defragmenting your data
• Enabling parallelism
• Using the right indexes
• Using the right data types
• Tuning your application

By following these tips, you can improve the performance of your Oracle 19c database and get the most out of your investment.