To protect your database, specify passwords for users SYS and SYSTEM.

• In the CREATE DATABASE statement, include clauses that specify the password for users SYS and SYSTEM.

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The clauses of the CREATE DATABASE statement used for specifying the passwords for users SYS and SYSTEM are:

• USER SYS IDENTIFIED BY password
• USER SYSTEM IDENTIFIED BY password

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If you omit these clauses, then these users are assigned the default passwords change_on_install and manager, respectively. A record is written to the alert log indicating that the default passwords were used. To protect your database, you must change these passwords using the ALTER USER statement immediately after database creation.

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Oracle strongly recommends that you specify these clauses, even though they are optional in this release of Oracle Database. The default passwords are commonly known, and if you neglect to change them later, then you leave database vulnerable to attack by malicious users.

When choosing a password, keep in mind that passwords are case-sensitive. Also, there may be password formatting requirements for your database. See the section entitled “How Oracle Database Checks the Complexity of Passwords” in Oracle Database Security Guide for more information.

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To create a hash cluster, you use the same CREATE CLUSTER statement as for an indexed cluster, with the addition of a hash key. The number of hash values for the cluster depends on the hash key.

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The cluster key, like the key of an indexed cluster, is a single column or composite key shared by the tables in the cluster. A hash key value is an actual or possible value inserted into the cluster key column. For example, if the cluster key is department_id, then hash key values could be 10, 20, 30, and so on.

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Oracle Database uses a hash function that accepts an infinite number of hash key values as input and sorts them into a finite number of buckets. Each bucket has a unique numeric ID known as a hash value. Each hash value maps to the database block address for the block that stores the rows corresponding to the hash key value (department 10, 20, 30, and so on).

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In the following example, the number of departments that are likely to exist is 100, so HASHKEYS is set to 100:

CopyCREATE CLUSTER employees_departments_cluster
   (department_id NUMBER(4))
SIZE 8192 HASHKEYS 100;

After you create employees_departments_cluster, you can create the employees and departments tables in the cluster. You can then load data into the hash cluster just as in the indexed cluster.

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You can use the CREATE DATABASE clauses to simplify the creation and management of your database.

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When you execute a CREATE DATABASE statement, Oracle Database performs at least these operations:

• Creates the data files for the database
• Creates the control files for the database
• Creates the online redo logs for the database and establishes the ARCHIVELOG mode

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• Creates the SYSTEM tablespace
• Creates the SYSAUX tablespace
• Creates the data dictionary
• Sets the character set that stores data in the database
• Sets the database time zone
• Mounts and opens the database for use

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A hash cluster is like an indexed cluster, except the index key is replaced with a hash function. No separate cluster index exists. In a hash cluster, the data is the index.

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With an indexed table or indexed cluster, Oracle Database locates table rows using key values stored in a separate index. To find or store a row in an indexed table or table cluster, the database must perform at least two I/Os:

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• One or more I/Os to find or store the key value in the index
• Another I/O to read or write the row in the table or table cluster

To find or store a row in a hash cluster, Oracle Database applies the hash function to the cluster key value of the row. The resulting hash value corresponds to a data block in the cluster, which the database reads or writes on behalf of the issued statement.

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Hashing is an optional way of storing table data to improve the performance of data retrieval. Hash clusters may be beneficial when the following conditions are met:

• A table is queried much more often than modified.
• The hash key column is queried frequently with equality conditions, for example, WHERE department_id=20. For such queries, the cluster key value is hashed. The hash key value points directly to the disk area that stores the rows.
• You can reasonably guess the number of hash keys and the size of the data stored with each key value.

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When you execute a CREATE DATABASE statement, Oracle Database performs several operations. The actual operations performed depend on the clauses that you specify in the CREATE DATABASE statement and the initialization parameters that you have set.

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• About CREATE DATABASE Statement Clauses
  You can use the CREATE DATABASE clauses to simplify the creation and management of your database.
• Protecting Your Database: Specifying Passwords for Users SYS and SYSTEM
  To protect your database, specify passwords for users SYS and SYSTEM.

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• Creating a Locally Managed SYSTEM Tablespace
  During database creation, create a locally managed SYSTEM tablespace. A locally managed tablespace uses a bitmap stored in each data file to manage the extents.
• Specify Data File Attributes for the SYSAUX Tablespace
  The SYSAUX tablespace is created by default, but you can specify its data file attributes during database creation.
• Using Automatic Undo Management: Creating an Undo Tablespace
  Automatic undo management uses an undo tablespace.

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• Creating a Default Permanent Tablespace
  Oracle strongly recommends that you create a default permanent tablespace. Oracle Database assigns to this tablespace any non-SYSTEM users for whom you do not explicitly specify a different permanent tablespace.
• Creating a Default Temporary Tablespace
  When you create a default temporary tablespace, Oracle Database assigns it as the temporary tablespace for users who are not explicitly assigned a temporary tablespace.
• Specifying Oracle Managed Files at Database Creation
  You can minimize the number of clauses and parameters that you specify in your CREATE DATABASE statement by using the Oracle Managed Files feature.
• Supporting Bigfile Tablespaces During Database Creation
  Oracle Database simplifies management of tablespaces and enables support for extremely large databases by letting you create bigfile tablespaces.
• Specifying the Database Time Zone and Time Zone File
  Oracle Database datetime and interval data types and time zone support make it possible to store consistent information about the time of events and transactions.
• Specifying FORCE LOGGING Mode
  Some data definition language statements (such as CREATE TABLE) allow the NOLOGGING clause, which causes some database operations not to generate redo records in the database redo log. The NOLOGGING setting can speed up operations that can be easily recovered outside of the database recovery mechanisms, but it can negatively affect media recovery and standby databases.

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An index cluster is a table cluster that uses an index to locate data. The cluster index is a B-tree index on the cluster key. A cluster index must be created before any rows can be inserted into clustered tables.

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Example 2-6 Creating a Table Cluster and Associated Index

Assume that you create the cluster employees_departments_cluster with the cluster key department_id, as shown in the following example:

CopyCREATE CLUSTER employees_departments_cluster
   (department_id NUMBER(4))
SIZE 512;

CREATE INDEX idx_emp_dept_cluster 
   ON CLUSTER employees_departments_cluster;

Because the HASHKEYS clause is not specified, employees_departments_cluster is an indexed cluster. The preceding example creates an index named idx_emp_dept_cluster on the cluster key department_id.

Example 2-7 Creating Tables in an Indexed Cluster

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You create the employees and departments tables in the cluster, specifying the department_id column as the cluster key, as follows (the ellipses mark the place where the column specification goes):

CopyCREATE TABLE employees ( ... )
   CLUSTER employees_departments_cluster (department_id);
 
CREATE TABLE departments ( ... )
   CLUSTER employees_departments_cluster (department_id);

Assume that you add rows to the employees and departments tables. The database physically stores all rows for each department from the employees and departments tables in the same data blocks. The database stores the rows in a heap and locates them with the index.

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Figure 2-5 shows the employees_departments_cluster table cluster, which contains employees and departments. The database stores rows for employees in department 20 together, department 110 together, and so on. If the tables are not clustered, then the database does not ensure that the related rows are stored together.

Figure 2-5 Clustered Table Data
Description of “Figure 2-5 Clustered Table Data”

The B-tree cluster index associates the cluster key value with the database block address (DBA) of the block containing the data. For example, the index entry for key 20 shows the address of the block that contains data for employees in department 20:

Copy20,AADAAAA9d

The cluster index is separately managed, just like an index on a nonclustered table, and can exist in a separate tablespace from the table cluster.

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Take a full backup of the database to ensure that you have a complete set of files from which to recover if a media failure occurs.

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• Back up the database.

Step 15: (Optional) Enable Automatic Instance Startup

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You might want to configure the Oracle instance to start automatically when its host computer restarts.

• Configure the Oracle instance to start automatically when its host computer restarts.

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See your operating system documentation for instructions. For example, on Windows, use the following command to configure the database service to start the instance upon computer restart: ORADIM -EDIT -SID sid -STARTMODE AUTO -SRVCSTART SYSTEM [-SPFILE]

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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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