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How to Check Table Fragmentation In Oracle?

6 minutes read

Table fragmentation in Oracle can be checked using the DBMS_SPACE package. This package provides procedures and functions to analyze and report on the space usage for a table or index. By using the DBMS_SPACE package, you can determine the level of fragmentation in a table by analyzing the free space in the table segments. This information can help you optimize the table storage and improve performance of the database.


One way to check table fragmentation in Oracle is to use the DBMS_SPACE.SPACE_USAGE procedure. This procedure takes the table name and schema as parameters and returns information about the space usage for the specified table. You can use this information to identify if the table is fragmented and plan for reorganization or defragmentation of the table.


Another method to check table fragmentation in Oracle is to query the DBA_SEGMENTS view. This view contains information about the segments (tablespaces, tables, and indexes) in the database. By querying the DBA_SEGMENTS view, you can retrieve information about the space usage for a specific table and identify any fragmentation issues.


Overall, checking table fragmentation in Oracle involves analyzing the space usage for the table segments and identifying any areas of concern that may impact the performance of the database. By monitoring and addressing table fragmentation issues, you can optimize the storage and performance of the Oracle database.


What tools can be used to check table fragmentation in Oracle?

  1. Oracle Enterprise Manager: The Oracle Enterprise Manager provides a user-friendly interface to monitor and manage database performance, including checking for table fragmentation.
  2. Oracle SQL Developer: This tool allows users to run SQL queries and scripts to analyze table fragmentation and performance issues.
  3. SQLPlus: SQLPlus is a command-line tool provided by Oracle that allows users to connect to Oracle databases and run SQL queries. Users can write custom queries to check for table fragmentation.
  4. Oracle Automatic Workload Repository (AWR): The AWR collects and maintains performance statistics of an Oracle database. It can be used to identify and analyze table fragmentation.
  5. APEX (Application Express): Oracle APEX provides a web-based interface for database management and querying. Users can use APEX to analyze table fragmentation and performance issues.
  6. DBMS_SPACE and PL/SQL scripts: Oracle provides built-in procedures and packages, such as DBMS_SPACE, that can be used to check for table fragmentation and space usage in a database. Users can also write custom PL/SQL scripts to analyze table fragmentation.


What techniques can be used to reduce table fragmentation in Oracle?

  1. Regularly analyze the database to identify fragmented tables and indexes. Oracle provides a built-in ANALYZE command to gather statistics on tables and indexes, which can help identify fragmentation.
  2. Reorganize or rebuild indexes on fragmented tables. The ALTER INDEX command can be used to rebuild or reorganize indexes, which helps to reduce fragmentation.
  3. Use the OPTIMIZE TABLE command to defragment tables. This command can be used to rearrange rows in a table to reduce fragmentation.
  4. Use tablespaces effectively to manage storage allocation for tables and indexes. Properly sizing and managing tablespaces can help reduce fragmentation and improve performance.
  5. Consider using partitioning to manage large tables and indexes more effectively. Partitioning can help distribute data across multiple physical storage locations, reducing fragmentation.
  6. Regularly monitor and manage the space usage in the database. Ensure that the database has enough free space for new data to be inserted without causing fragmentation.
  7. Consider using Automatic Segment Space Management (ASSM) to manage space allocation within tablespaces more efficiently. ASSM can help prevent fragmentation by automatically managing space allocation for segments.


How to identify fragmented tables in Oracle?

You can identify fragmented tables in Oracle by querying the data dictionary views USER_TABLES, USER_INDEXES, and USER_SEGMENTS. Here are steps to identify fragmented tables:

  1. Query USER_TABLES to identify tables in the database:
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SELECT table_name
FROM user_tables;


  1. Query USER_INDEXES to identify indexes on tables:
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SELECT index_name, table_name
FROM user_indexes;


  1. Query USER_SEGMENTS to identify segments (includes tables and indexes) with their size:
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SELECT segment_name, segment_type, bytes
FROM user_segments;


  1. Compare the size of tables and indexes to determine if there are significant size differences, which may indicate fragmentation. Fragmented tables will have larger sizes compared to their actual data size.
  2. You can also use the following query to check for the fragmentation ratio of tables in Oracle: 
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SELECT table_name, (SUM(bytes) / COUNT(*)) AS avg_fragmentation_ratio
FROM user_segments
WHERE segment_type = 'TABLE'
GROUP BY table_name;


By analyzing the data from these queries, you can identify tables that may be fragmented and take appropriate actions to defragment them using tools like Oracle's Segment Advisor.


How to calculate the amount of free space within a fragmented table in Oracle?

To calculate the amount of free space within a fragmented table in Oracle, you can use the following query:

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SELECT SUM(BLOCKS) * (SELECT VALUE FROM V$PARAMETER WHERE NAME = 'db_block_size') AS FREE_SPACE
FROM DBA_FREE_SPACE
WHERE TABLESPACE_NAME = 'your_tablespace_name'
AND SEGMENT_NAME = 'your_table_name';


Replace 'your_tablespace_name' with the name of the tablespace where the fragmented table is located, and 'your_table_name' with the name of the fragmented table.


This query will calculate the total amount of free space within the specified fragmented table by summing up the number of blocks and multiplying by the block size.


What is table fragmentation in Oracle?

Table fragmentation in Oracle occurs when the physical storage of a table's data is not stored in contiguous blocks on disk. This can happen over time as data is inserted, updated, and deleted from a table, causing the table's data to become spread out across multiple non-contiguous blocks. This fragmentation can lead to decreased performance and efficiency, as the database must perform additional I/O operations to access the fragmented data. It is important for database administrators to regularly monitor and address table fragmentation to ensure optimal performance of the Oracle database.


How to determine the fragmentation ratio of a table in Oracle?

To determine the fragmentation ratio of a table in Oracle, you can use the following steps:

  1. Identify the table you want to analyze for fragmentation.
  2. Execute the following query to retrieve the total number of blocks allocated to the table: 
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SELECT COUNT(*) AS total_blocks
FROM dba_segments
WHERE segment_name = 'YOUR_TABLE_NAME';


  1. Execute the following query to retrieve the number of blocks that are currently being used by the table:
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SELECT COUNT(*) AS used_blocks
FROM dba_extents
WHERE segment_name = 'YOUR_TABLE_NAME';


  1. Calculate the fragmentation ratio by dividing the number of used blocks by the total number of blocks, and multiply by 100 to get the percentage:
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SELECT (used_blocks / total_blocks) * 100 AS fragmentation_ratio
FROM (
    SELECT (SELECT COUNT(*) AS total_blocks
            FROM dba_segments
            WHERE segment_name = 'YOUR_TABLE_NAME') AS total_blocks,
           (SELECT COUNT(*) AS used_blocks
            FROM dba_extents
            WHERE segment_name = 'YOUR_TABLE_NAME') AS used_blocks
  );


The result will be the fragmentation ratio of the table in terms of percentage. A lower percentage indicates that the table is less fragmented, while a higher percentage indicates more fragmentation.

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