By default, the database locks all rows in the compression unit if an update or delete is applied to any row in the unit. To avoid this issue, you can choose to enable row-level locking for a table. In this case, the database only locks rows that are affected by the update or delete operation.

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See also

• “Automatic Segment Space Management”
• “Row Locks (TX)”
• Oracle Database Administrator’s Guide to learn how to perform conventional inserts
• Oracle Database SQL Language Reference to learn about the INSERT statement

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Overview of Table Clusters

A table cluster is a group of tables that share common columns and store related data in the same blocks.

When tables are clustered, a single data block can contain rows from multiple tables. For example, a block can store rows from both the employees and departments tables rather than from only a single table.

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The cluster key is the column or columns that the clustered tables have in common. For example, the employees and departments tables share the department_id column. You specify the cluster key when creating the table cluster and when creating every table added to the table cluster.

The cluster key value is the value of the cluster key columns for a particular set of rows. All data that contains the same cluster key value, such as department_id=20, is physically stored together. Each cluster key value is stored only once in the cluster and the cluster index, no matter how many rows of different tables contain the value.

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For an analogy, suppose an HR manager has two book cases: one with boxes of employee folders and the other with boxes of department folders. Users often ask for the folders for all employees in a particular department. To make retrieval easier, the manager rearranges all the boxes in a single book case. She divides the boxes by department ID. Thus, all folders for employees in department 20 and the folder for department 20 itself are in one box; the folders for employees in department 100 and the folder for department 100 are in another box, and so on.

Consider clustering tables when they are primarily queried (but not modified) and records from the tables are frequently queried together or joined. Because table clusters store related rows of different tables in the same data blocks, properly used table clusters offer the following benefits over nonclustered tables:

• Disk I/O is reduced for joins of clustered tables.
• Access time improves for joins of clustered tables.
• Less storage is required to store related table and index data because the cluster key value is not stored repeatedly for each row.

Typically, clustering tables is not appropriate in the following situations:

• The tables are frequently updated.
• The tables frequently require a full table scan.
• The tables require truncating.

You may want to run other scripts. The scripts that you run are determined by the features and options you choose to use or install.

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• Run scripts to install additional options.

Many of the scripts available to you are described in the Oracle Database Reference.

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If you plan to install other Oracle products to work with this database, then see the installation instructions for those products. Some products require you to create additional data dictionary tables. Usually, command files are provided to create and load these tables into the database data dictionary.

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See your Oracle documentation for the specific products that you plan to install for installation and administration instructions.

Step 13: Run Datapatch

Run Datapatch to update information stored in the database to the correct patch level.

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Hybrid Columnar Compression has implications for row locking in different types of DML operations.

Direct Path Loads and Conventional Inserts

When loading data into a table that uses Hybrid Columnar Compression, you can use either conventional inserts or direct path loads. Direct path loads lock the entire table, which reduces concurrency.

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Oracle Database 12c Release 2 (12.2) adds support for conventional array inserts into the Hybrid Columnar Compression format. The advantages of conventional array inserts are:

• Inserted rows use row-level locks, which increases concurrency.
• Automatic Data Optimization (ADO) and Heat Map support Hybrid Columnar Compression for row-level policies. Thus, the database can use Hybrid Columnar Compression for eligible blocks even when DML activity occurs on other parts of the segment.

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When the application uses conventional array inserts, Oracle Database stores the rows in compression units when the following conditions are met:

• The table is stored in an ASSM tablespace.
• The compatibility level is 12.2.0.1 or later.
• The table definition satisfies the existing Hybrid Columnar Compression table constraints, including no columns of type LONG, and no row dependencies.

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Conventional inserts generate redo and undo. Thus, compression units created by conventional DML statement are rolled back or committed along with the DML. The database automatically performs index maintenance, just as for rows that are stored in conventional data blocks.

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Start an instance without mounting a database.

• Run the STARTUP command with the NOMOUNT clause.

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Typically, you do this only during database creation or while performing maintenance on the database. In this example, because the initialization parameter file or server parameter file is stored in the default location, you are not required to specify the PFILE clause:

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Step 9: Issue the CREATE DATABASE Statement

To create the new database, use the CREATE DATABASE statement.

• Run the CREATE DATABASE statement.

Step 10: Create Additional Tablespaces

To make the database functional, you must create additional tablespaces for your application data.

• Run the CREATE TABLESPACE statement to create additional tablespaces.

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Step 11: Run Scripts to Build Data Dictionary Views

Run the scripts necessary to build data dictionary views, synonyms, and PL/SQL packages, and to support proper functioning of SQL*Plus.

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Hybrid Columnar Compression uses a logical construct called a compression unit to store a set of rows.

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When you load data into a table, the database stores groups of rows in columnar format, with the values for each column stored and compressed together. After the database has compressed the column data for a set of rows, the database fits the data into the compression unit.

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For example, you apply Hybrid Columnar Compression to a daily_sales table. At the end of every day, you populate the table with items and the number sold, with the item ID and date forming a composite primary key. The following table shows a subset of the rows in daily_sales.

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Table 2-2 Sample Table daily_sales

Item_ID	Date	Num_Sold	Shipped_From	Restock
1000	01-JUN-18	2	WAREHOUSE1	Y
1001	01-JUN-18	0	WAREHOUSE3	N
1002	01-JUN-18	1	WAREHOUSE3	N
1003	01-JUN-14	0	WAREHOUSE2	N
1004	01-JUN-18	2	WAREHOUSE1	N
1005	01-JUN-18	1	WAREHOUSE2	N

Assume that this subset of rows is stored in one compression unit. Hybrid Columnar Compression stores the values for each column together, and then uses multiple algorithms to compress each column. The database chooses the algorithms based on a variety of factors, including the data type of the column, the cardinality of the actual values in the column, and the compression level chosen by the user.

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As shown in the following graphic, each compression unit can span multiple data blocks. The values for a particular column may or may not span multiple blocks.

Figure 2-4 Compression Unit
Description of “Figure 2-4 Compression Unit”

If Hybrid Columnar Compression does not lead to space savings, then the database stores the data in the DBMS_COMPRESSION.COMP_BLOCK format. In this case, the database applies OLTP compression to the blocks, which reside in a Hybrid Columnar Compression segment.

Start SQL*Plus and connect to your Oracle Database instance with the SYSDBA administrative privilege.

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• To authenticate with a password file, enter the following commands, and then enter the SYS password when prompted: $ sqlplus /nolog SQL> CONNECT SYS AS SYSDBA
• To authenticate with operating system authentication, enter the following commands: $ sqlplus /nolog SQL> CONNECT / AS SYSDBA

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Step 7: Create a Server Parameter File

The server parameter file enables you to change initialization parameters with the ALTER SYSTEM command and persist the changes across a database shutdown and startup. You create the server parameter file from your edited text initialization file.

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This SQL*Plus command reads the text initialization parameter file (PFILE) with the default name from the default location, creates a server parameter file (SPFILE) from the text initialization parameter file, and writes the SPFILE to the default location with the default SPFILE name.

You can also supply the file name and path for both the PFILE and SPFILE if you are not using default names and locations.

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If your underlying storage supports Hybrid Columnar Compression, then you can specify different types of compression, depending on your requirements.

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The compression options are:

• Warehouse compressionThis type of compression is optimized to save storage space, and is intended for data warehouse applications.
• Archive compressionThis type of compression is optimized for maximum compression levels, and is intended for historical data and data that does not change.

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Hybrid Columnar Compression is optimized for data warehousing and decision support applications on Oracle Exadata storage. Oracle Exadata maximizes the performance of queries on tables that are compressed using Hybrid Columnar Compression, taking advantage of the processing power, memory, and Infiniband network bandwidth that are integral to the Oracle Exadata storage server.

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Other Oracle storage systems support Hybrid Columnar Compression, and deliver the same space savings as on Oracle Exadata storage, but do not deliver the same level of query performance. For these storage systems, Hybrid Columnar Compression is ideal for in-database archiving of older data that is infrequently accessed.

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On the Windows platform, before you can connect to an instance, you must manually create it if it does not already exist. The ORADIM command creates an Oracle Database instance by creating a new Windows service.

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To create an instance:

• Enter the following command at a Windows command prompt: oradim -NEW -SID sid -STARTMODE MANUAL -PFILE file

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Replace the following placeholders with appropriate values:

• sid – The desired SID (for example mynewdb)
• file – The full path to the text initialization parameter file

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Most Oracle Database services log on to the system using the privileges of the Oracle Home User. The service runs with the privileges of this user. The ORADIM command prompts you for the password to this user account. You can specify other options using ORADIM.

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When an Oracle instance starts, it reads an initialization parameter file. This file can be a text file, which can be created and modified with a text editor, or a binary file, which is created and dynamically modified by the database. The binary file, which is preferred, is called a server parameter file. In this step, you create a text initialization parameter file. In a later step, you create a server parameter file from the text file.

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• Create the initialization parameter file.

One way to create the text initialization parameter file is to edit the sample presented in “Sample Initialization Parameter File”.

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If you create the initialization parameter file manually, ensure that it contains at least the parameters listed in Table 2-2. All other parameters not listed have default values.

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For convenience, store your initialization parameter file in the Oracle Database default location, using the default file name. Then when you start your database, it will not be necessary to specify the PFILE clause of the STARTUP command, because Oracle Database automatically looks in the default location for the initialization parameter file.

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You must be authenticated and granted appropriate system privileges in order to create a database.

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• Decide on an authentication method.

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You can be authenticated as an administrator with the required privileges in the following ways:

• With a password file
• With operating system authentication

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To be authenticated with a password file, create the password file as described in “Creating and Maintaining a Database Password File”. To be authenticated with operating system authentication, ensure that you log in to the host computer with a user account that is a member of the appropriate operating system user group. On the UNIX and Linux platforms, for example, this is typically the dba user group. On the Windows platform, the user installing the Oracle software is automatically placed in the required user group.

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