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Estimate Object's Size enables the DBA to estimate the size of selected DB objects according to the selected estimation method.

The estimation methods differ from one another by the technique for performing the estimation and by the time consumed for performing the estimation.

The program estimates the objects' size without a need to run analyze on the objects (except the estimation method - 'Statistics').

To Estimate Object's Size:

1        Select objects from the Rebuilder.

2        Right click on the objects and choose Estimate Size.

3        Define Estimation method:

• Data size
• Block being used
• High Water Mark
• Allocated size
• Statistics
• Object's Size
• Object's Rows
• Sampled Data & Predicted Size - see 'Capacity Planning Pack'

4        Click OK.

Data size - Summarize the size of all table rows

This method is available only for tables that are not empty.

Estimation Size = summarize of all table actual rows size.

The method is the highest DB time consuming, especially for large tables.

Block being used - Look for blocks that are actually in use, and summarize their size

This method is available only for tables that are not empty.

Estimation Size = summarize of all table IN USE blocks size.

The method has high DB time consuming, especially for large tables.

High Water Mark – Summarize the size of all blocks below High Water Mark

This method is the default method.

Estimation Size = the highest point that the data inside the object captured since ever.

Allocated size – All space allocated by the segment on the Tablespace

Estimation Size = the size which is allocated for the object in the tablespace, actually copy of the size field.

Statistics - Use statistics values

This method can be used only if the object has statistics in the DB.

The estimation size is calculated according to the object statistics.

Object's Size

This method is being used when the exact object size is known.

Estimation Size = the size given by the user.

Object's Rows

The estimation size is calculated based on the following variables: object rows number, average row length and PCTFREE (taken from the Object).

Example:

1. Datafile.

2. Two Extents of a Table. The first one has 15 blocks (15 * 8KB = 120KB), the second has 10 blocks (10 * 8KB = 80KB).

3. High Water Mark (marks the last block ever been used in the table).

4. Blocks above the High Water Mark (Never been used).

5. Rows of the table (every row can take a different amount of space in the block).

6. Empty blocks below High Water Mark (The rows in them were deleted from the table).

The table has two extents, first extent: 120KB, second extent: 80KB.

Total table size allocated on the Tablespace: 200KB.

Database DB_BLOCK_SIZE: 8KB.

Estimation methods

• 'Allocated size' estimation method returns the total size allocated by the extents of the table. In this case: 200KB.

•  'High Water Mark' estimation method returns the size of all the blocks that were never been used in the table (below High Water Mark). In this case: 19 * 8KB = 152KB.

• 'Blocks being used' estimation method returns the size of all the blocks in which table rows exist. In this case: 17 * 8KB = 136KB.

•  'Data size' estimation method returns the summary of all the rows size. In this case: ~100KB.