Notify me of new comments via email. Notify me of new posts via email. This site uses Akismet to reduce spam. Learn how your comment data is processed. Tablespace Segment space management automatic and manual in Oracle Segment size management manual vs segment size management auto: AUTOMATIC Segment Space management in tablespace used bitmap for tracking the freelist, it remove use of freelist management which cause the contention on the segment header that occurs with freelists management.
Like this: Like Loading Prior to Oracle 9i, each block had to be read so the freelist could be checked to see if there was room in the block. In 9i, the bitmap can be checked reducing the number of blocks read unneccessarily. The bitmap is constantly kept up to date with changes to the block making freespace management easier and reducing wasted space as blocks can be kept fuller since the overhead of freelist processing has been reduced.
This organization allows index-like searches for free blocks. Note:Automatic segment space management is the default for all new permanent, locally managed tablespaces. Note: Create your tablespaces with the locally managed and automatic segment space management features ASSM enabled. Modify or switch between automatic or Manual space management Note: There is no way to convert the tablespace from automatic to manually or vise versa. Simple method is create a new tablespace with desired options and move the objects from the old tablespace to new tablespace.
Otherwise, the tablespace is locally managed and autoallocated. The following example creates a tablespace with uniform K extents. In a database with 2K blocks, each extent would be equivalent to 64 database blocks.
Each K extent is represented by a bit in the extent bitmap for this file. In a locally managed tablespace, there are two methods that Oracle Database can use to manage segment space: automatic and manual. Manual segment space management uses linked lists called "freelists" to manage free space in the segment, while automatic segment space management uses bitmaps.
Automatic segment space management is the more efficient method, and is the default for all new permanent, locally managed tablespaces. Automatic segment space management delivers better space utilization than manual segment space management.
It is also self-tuning, in that it scales with increasing number of users or instances. In an Oracle Real Application Clusters environment, automatic segment space management allows for a dynamic affinity of space to instances. In addition, for many standard workloads, application performance with automatic segment space management is better than the performance of a well-tuned application using manual segment space management. The following statement creates tablespace lmtbsb with automatic segment space management:.
The segment space management that you specify at tablespace creation time applies to all segments subsequently created in the tablespace. You cannot change the segment space management mode of a tablespace. Locally managed tablespaces using automatic segment space management can be created as single-file or bigfile tablespaces, as described in "Bigfile Tablespaces". You cannot alter a locally managed tablespace to a locally managed temporary tablespace, nor can you change its method of segment space management.
Coalescing free extents is unnecessary for locally managed tablespaces. See "Altering Tablespace Availability". See "Using Read-Only Tablespaces". Renaming a datafile, or enabling or disabling the autoextension of the size of a datafile in the tablespace. See Chapter 9, "Managing Datafiles and Tempfiles". A bigfile tablespace is a tablespace with a single, but very large up to 4G blocks datafile.
Traditional smallfile tablespaces, in contrast, can contain multiple datafiles, but the files cannot be as large. The benefits of bigfile tablespaces are the following:. A bigfile tablespace with 8K blocks can contain a 32 terabyte datafile. A bigfile tablespace with 32K blocks can contain a terabyte datafile.
The maximum number of datafiles in an Oracle Database is limited usually to 64K files. Therefore, bigfile tablespaces can significantly enhance the storage capacity of an Oracle Database.
Bigfile tablespaces can reduce the number of datafiles needed for a database. Bigfile tablespaces simplify database management by providing datafile transparency. Bigfile tablespaces are supported only for locally managed tablespaces with automatic segment space management, with three exceptions: locally managed undo tablespaces, temporary tablespaces, and the SYSTEM tablespace.
Bigfile tablespaces are intended to be used with Automatic Storage Management ASM or other logical volume managers that supports striping or RAID, and dynamically extensible logical volumes. Avoid creating bigfile tablespaces on a system that does not support striping because of negative implications for parallel query execution and RMAN backup parallelization.
Using bigfile tablespaces on platforms that do not support large file sizes is not recommended and can limit tablespace capacity. Refer to your operating system specific documentation for information about maximum supported file sizes. Oracle Database automatically creates a locally managed tablespace with automatic segment space management. For example:. A bigfile tablespace is created by default.
You can also identify a bigfile tablespace by the relative file number of its single datafile. A temporary tablespace contains transient data that persists only for the duration of the session. Temporary tablespaces can improve the concurrency of multiple sort operations, reduce their overhead, and avoid Oracle Database space management operations. Within a temporary tablespace, all sort operations for a given instance and tablespace share a single sort segment.
Sort segments exist for every instance that performs sort operations within a given tablespace. The sort segment is created by the first statement that uses a temporary tablespace for sorting, after startup, and is released only at shutdown. An extent cannot be shared by multiple transactions. Oracle Database Security Guide for information about creating users and assigning temporary tablespaces. Oracle Database Performance Tuning Guide for a discussion on tuning sorts.
Because space management is much simpler and more efficient in locally managed tablespaces, they are ideally suited for temporary tablespaces. Locally managed temporary tablespaces use tempfiles , which do not modify data outside of the temporary tablespace or generate any redo for temporary tablespace data.
Because of this, they enable you to perform on-disk sorting operations in a read-only or standby database. You also use different views for viewing information about tempfiles than you would for datafiles.
The following statement creates a temporary tablespace in which each extent is 16M. Each 16M extent which is the equivalent of blocks when the standard block size is 2K is represented by a bit in the bitmap for the file.
The extent management clause is optional for temporary tablespaces because all temporary tablespaces are created with locally managed extents of a uniform size. But if you want to specify another value for SIZE , you can do so as shown in the preceding statement.
Just as for regular tablespaces, you can create single-file bigfile temporary tablespaces. See the sections "Creating a Bigfile Tablespace" and "Altering a Bigfile Tablespace" for information about bigfile tablespaces, but consider that you are creating temporary tablespaces that use tempfiles instead of datafiles.
The following statements take offline and bring online tempfiles. The tablespace to which this tempfile belonged remains.
A message is written to the alert log for the datafile that was deleted. If an operating system error prevents the deletion of the file, the statement still succeeds, but a message describing the error is written to the alert log. A tablespace group enables a user to consume temporary space from multiple tablespaces.
A tablespace group has the following characteristics:. It contains at least one tablespace. There is no explicit limit on the maximum number of tablespaces that are contained in a group. You can specify a tablespace group name wherever a tablespace name would appear when you assign a default temporary tablespace for the database or a temporary tablespace for a user. You do not explicitly create a tablespace group. Rather, it is created implicitly when you assign the first temporary tablespace to the group.
The group is deleted when the last temporary tablespace it contains is removed from it. Using a tablespace group, rather than a single temporary tablespace, can alleviate problems caused where one tablespace is inadequate to hold the results of a sort, particularly on a table that has many partitions. A tablespace group enables parallel execution servers in a single parallel operation to use multiple temporary tablespaces.
For example, if neither group1 nor group2 exists, then the following statements create those groups, each of which has only the specified tablespace as a member:. The following statement adds a tablespace to an existing group. It creates and adds tablespace lmtemp3 to group1 , so that group1 contains tablespaces lmtemp2 and lmtemp3. The following statement also adds a tablespace to an existing group, but in this case because tablespace lmtemp2 already belongs to group1 , it is in effect moved from group1 to group2 :.
Now group2 contains both lmtemp and lmtemp2 , while group1 consists of only tmtemp3. Tablespace lmtemp3 no longer belongs to any group. Further, since there are no longer any members of group1 , this results in the implicit deletion of group1. Any user who has not explicitly been assigned a temporary tablespace will now use tablespaces lmtemp and lmtemp2.
If a tablespace group is specified as the default temporary tablespace, you cannot drop any of its member tablespaces. You must first remove the tablespace from the tablespace group. Likewise, you cannot drop a single temporary tablespace as long as it is the default temporary tablespace. This feature lets you transport tablespaces with unlike block sizes between databases.
For some database operations, you can control whether the database generates redo records. Without redo, no media recovery is possible. However, suppressing redo generation can improve performance, and may be appropriate for easily recoverable operations. If you do not include this clause, or if you specify LOGGING instead, then the database generates redo when changes are made to objects in the tablespace.
Redo is never generated for temporary segments or in temporary tablespaces, regardless of the logging attribute. The logging attribute specified at the tablespace level is the default attribute for objects created within the tablespace. This overrides any specification made at the object level. You can take an online tablespace offline so that it is temporarily unavailable for general use.
The rest of the database remains open and available for users to access data. Conversely, you can bring an offline tablespace online to make the schema objects within the tablespace available to database users. The database must be open to alter the availability of a tablespace. You may want to take a tablespace offline for any of the following reasons:. To make a portion of the database unavailable while allowing normal access to the remainder of the database.
To perform an offline tablespace backup even though a tablespace can be backed up while online and in use. To make an application and its group of tables temporarily unavailable while updating or maintaining the application. Before taking a tablespace offline, consider altering the tablespace allocation of any users who have been assigned the tablespace as a default tablespace. Doing so is advisable because those users will not be able to access objects in the tablespace while it is offline.
If no files are offline, but you use the temporary clause, media recovery is not required to bring the tablespace back online. However, if one or more files of the tablespace are offline because of write errors, and you take the tablespace offline temporarily, the tablespace requires recovery before you can bring it back online.
In this case, only the files taken offline because of errors need to be recovered before the tablespace can be brought online. You can bring any tablespace in an Oracle Database online whenever the database is open.
A tablespace is normally online so that the data contained within it is available to database users. Otherwise, the database returns an error and the tablespace remains offline. Oracle Database Backup and Recovery Basics. Making a tablespace read-only prevents write operations on the datafiles in the tablespace.
The primary purpose of read-only tablespaces is to eliminate the need to perform backup and recovery of large, static portions of a database. Read-only tablespaces also provide a way to protecting historical data so that users cannot modify it. Making a tablespace read-only prevents updates on all tables in the tablespace, regardless of a user's update privilege level. You can drop items, such as tables or indexes, from a read-only tablespace, but you cannot create or alter objects in a read-only tablespace.
Read-only tablespaces can be transported to other databases. The tablespace must be online. This is necessary to ensure that there is no undo information that needs to be applied to the tablespace. The tablespace must not currently be involved in an online backup, because the end of a backup updates the header file of all datafiles in the tablespace.
For better performance while accessing data in a read-only tablespace, you can issue a query that accesses all of the blocks of the tables in the tablespace just before making it read-only. This eliminates the need for the database to check the status of the transactions that most recently modified the blocks. After the statement is issued, the tablespace is put into a transitional read-only state.
No transactions are allowed to make further changes using DML statements to the tablespace. If a transaction attempts further changes, it is terminated and rolled back.
However, transactions that already made changes and that attempt no further changes are allowed to commit or roll back. You can then notify the owners of those transactions and decide whether to terminate the transactions, if necessary.
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