Oracle Tablespaces and ASM Management

Oracle Database Storage ### Introduction to Oracle Tablespaces - Oracle database storage isn't a single large pool; it's divided into logical entities known as tablespaces. - Tablespaces provide a higher-level abstraction for storage management. - Tablespaces are composed of one or more physical files which can reside in either: - Operating System (OS) file system - Automatic Storage Management (ASM) - The Database Administrator (DBA) manages the addition or removal of tablespaces based on security and manageability needs. ### User Interaction with Tablespaces - Each database user is assigned a default tablespace. - With appropriate permissions and quotas, users can create database objects in any tablespace within the database. - A database object (such as a table, index, or partition) can reside in only one tablespace but may span across multiple physical data files. ### Understanding Oracle ASM - Oracle ASM (Automatic Storage Management) is a system that simplifies database storage management by substituting the OS file system manager. - ASM allows for the easy addition of disk space: - When disk space is added to a disk group, it becomes immediately available for any tablespace using that group. - Most tablespaces are utilized for storing user tables and data, comprising the largest storage footprint in a database. ### Types of Tablespaces 1. Permanent Tablespaces - These hold the majority of user-defined data. - Objects within these spaces are visible to users.

  1. Temporary Tablespaces - Used for temporary segments and operations (e.g., sorting, grouping) that cannot be processed in memory. - Unlike permanent tablespaces, users do not interact directly with temporary tables.

  2. Undo Tablespaces - These are crucial for transaction management. - They store changes made to table rows during a transaction, allowing for rollback to the transaction's initial state if necessary. ### Default Tablespaces Upon Installation - An Oracle database installation automatically creates several tablespaces: - System Tablespace - Contains objects owned by SYS and other critical metadata. - Loss of this tablespace can halt the database.

  • SYSOX Tablespace - Stores non-critical historical metadata. - Database operational integrity is not impacted if this tablespace is lost.

  • Temp Tablespace - Stores temporary segments for operations that cannot fit in memory.

  • Undo Tablespace - Holds redo images necessary for rolling back transactions.

  • User Tablespaces - Default spaces for non-system users. Additional user tablespaces can be created for better disk space management, backup, and maintenance. ### Creating Tablespaces - Syntax for creating a tablespace is as follows: sql CREATE TABLESPACE tablespacename ...; - Each tablespace type has unique attributes and clauses. - Common components include: - Location of the data file - Initial size of the data file - Automatic growth settings - Growth increment size - Small File Tablespaces: Composed of multiple data files up to 32 GB. - Big File Tablespaces: Contains a single data file that can grow up to 32 TB. - Regardless of storage location (OS or ASM), data file structures are consistent, but management is simpler with ASM. ### Clauses and Best Practices - When creating any tablespace (especially permanent ones), there are many clauses and options. Common clauses include: - Specification of data file location - Initial and maximum size settings - Configuration for automatic growth with specified extension sizes - Implementing upper limits on file size to manage risks from runaway processes. ### Checking Disk Space Prerequisites - Before creating a new tablespace, assess available storage: - Use a query against the view v$asm_diskgroup to review: - Available disk groups - Total space in each disk group - Remaining free space - Example: - If only one disk group named data exists, check the free space (e.g., 400 GB). - When creating a tablespace, if it's a big file tablespace starting at 1 GB and auto-expanding by 500 MB, ensure total max size (1 TB) does not exceed available storage. ### Final Notes on Tablespace Management - Periodically review the total maximum size parameters to ensure sufficient disk space in ASM for expansions. - Understanding key combinations of clauses is essential for creating usable tablespaces. - Maintaining oversight of available disk space is critical, especially when creating tablespaces for various environments (production, QA, development).