Database Administrator has to provide table_name and schema_name as input to this query. Select table_name,bytes/(1024*1024*1024) from dba_table where table_name='&table_name' īelow query will show the total size of table with fragmentation, expected without fragmentation and how much % of size we can reclaim after removing table fragmentation. Now again check table size using and will find reduced size of the table. Other wise i would suggest to gather table stats to get updated stats.Įxec dbms_stats.gather_table_stats('&schema_name','&table_name') If this value is recent you can skip this step. Check LAST_ANALYZED value for table in dba_tables. So, We have to have updated stats on the table stored in dba_tables. The difference between these value will report actual fragmentation to DBA. To check exact difference in table actual size (dba_segments) and stats size (dba_tables). Steps to Check and Remove Table Fragmentation:. This all is due to fragmentation in the table or stats for table are not updated into dba_tables. In Oracle schema there are tables which has huge difference in actual size (size from User_segments) and expected size from user_tables (Num_rows*avg_row_length (in bytes)).

Note: Index based queries may not get that much benefited by reorg as compared to queries which does Full table scan. What are the reasons to reorganization of table?Ī) Slower response time (from that table)ī) High number of chained (actually migrated) rows.Ĭ) Table has grown many folds and the old space is not getting reused. Since Oracle knows that blocks beyond the high water mark don't have data, it only reads blocks up to the high water mark when doing a full table scan. Blocks below the high water mark (used blocks) have at least once contained data. HWM is an indicator of USED BLOCKS in the database. When a lot of DML operations are applied on a table, the table will become fragmented because DML does not release free space from the table below the HWM. Note that table fragmentation is different from file fragmentation. When rows are not stored contiguously, or if rows are split onto more than one block, performance decreases because these rows require additional block accesses.

To understand it more clearly, we need to be clear on how oracle manages space for tables. This leaves behind holes in table which results in table fragmentation. The space which gets freed up during non-insert DML operations is not immediately re-used (or sometimes, may not get reuse ever at all). If a table is only subject to inserts, there will not be any fragmentation.įragmentation comes with when we update/delete data in table.

How to find Table Fragmentation in Oracle Database

Oracle 10g tablespace fragmentation