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Don Burleson Blog 








Get Oracle table size

Oracle Database Tips by Donald Burleson


Question:  What script do I run to get the size of a table?


Answer:  First, we must remember that Oracle table size is constantly changing as DML adds and re moves rows.  Also, we have many other factors that determine the "actual" size of a table:

  • The high water mark for the Oracle table

  • The number of allocated extents

  • The amount of spaced reserved on each block for row expansion (pctfree)

You need to ask yourself exactly which Oracle table size, you wish to query:

  • Do you want only the row space consumed? ( select avg_row_len*num_rows from dba_tables)

  • Do you want to include allocated file space for the table? (select . . . from dba_segments)

  • Do you want to include un-used extent space? (select . . . from dba_data_files, dba_extents . . )

  • Do you want to include un-used space up to the high water mark?  This may over-estimate the real Oracle table size.

  • Do you want table sizes for Oracle growth monitoring?

There are many Oracle scripts for computing the size of a table, depending on these factors, but the best is the Oracle script collection which has many scripts to compute table sizes, depending on your needs.


   segment_name           table_name,   
   sum(bytes)/(1024*1024) table_size_meg
   segment_name = 'MYTAB'
See code depot for full scripts.


In  Oracle 10g we have the dba_hist_seg_stat table with a wealth of information about all active segments within the database, including the space usage in the space_allocated_total and space_used_total columns.

This script will show "spaced used total" for a specific Oracle table, essentiall computing the Oracle table size over time:

col c1 format a15 heading 'snapshot|date'
col c2 format a25 heading 'table|name'
col c3 format 999,999,999 heading 'space|used|total'
   to_char(begin_interval_time,'yy/mm/dd hh24:mm')     c1,
   object_name      c2,
   space_used_total c3
   dba_hist_seg_stat       s,
   dba_hist_seg_stat_obj   o,
   dba_hist_snapshot       sn
   o.owner = 'SCHEMA_07'
   s.obj# = o.obj#
   sn.snap_id = s.snap_id
   object_name like 'XIF2%'
order by

As I note in my book Oracle Tuning: The Definitive Reference, we can quickly plot this information for trending and predictions:

snapshot        table
date            name                      SPACE_USED_TOTAL
--------------- ------------------------- ----------
06/03/24 07:03  XIF2IMM_FLIGHT_OCCURRENCE    24,340
06/03/26 07:03  XIF2IMM_FLIGHT_OCCURRENCE    34,468






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