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sp_estimate_data_compression_savings (Transact-SQL)

Returns the current size of the requested object and estimates the object size for the requested compression state. Compression can be evaluated for whole tables or parts of tables. This includes heaps, clustered indexes, nonclustered indexes, indexed views, and table and index partitions. The objects can be compressed by using row compression or page compression. If the table, index, or partition is already compressed, you can use this procedure to estimate the size of the table, index, or partition if it is recompressed.

NoteNote

Compression and sp_estimate_data_compression_savings are available only in the SQL Server 2008 Enterprise and Developer editions.

To estimate the size of the object if it were to use the requested compression setting, this stored procedure samples the source object and loads this data into an equivalent table and index created in tempdb. The table or index create in tempdb is then compressed to the requested setting and the estimated compression savings is computed.

To change the compression state of a table, index, or partition, use the ALTER TABLE or ALTER INDEX statements. For general information about compression, see Creating Compressed Tables and Indexes.

NoteNote

If the existing data is fragmented, you might be able to reduce its size without using compression by rebuilding the index. For indexes, the fill factor will be applied during an index rebuild. This could increase the size of the index.

Topic link icon Transact-SQL Syntax Conventions


sp_estimate_data_compression_savings 
     [ @schema_name = ] 'schema_name'  
   , [ @object_name = ] 'object_name' 
   , [@index_id = ] index_id 
   , [@partition_number = ] partition_number 
   , [@data_compression = ] 'data_compression' 
[;]
[ @schema_name= ] 'schema_name'

Is the name of the database schema that contains the table or indexed view. schema_name is sysname. If schema_name is NULL, the default schema of the current user is used.

[ @object_name= ] 'object_name'

Is the name of the table or indexed view that the index is on. object_name is sysname.

[ @index_id= ] 'index_id'

Is the ID of the index. index_id is int, and can be one of the following values: the ID number of an index, NULL, or 0 if object_id is a heap. To return information for all indexes for a base table or view, specify NULL. If you specify NULL, you must also specify NULL for partition_number.

[ @partition_number= ] 'partition_number'

Is the partition number in the object. partition_number is int, and can be one of the following values: the partition number of an index or heap, NULL or 1 for a nonpartitioned index or heap.

To specify the partition, you can also specify the $partition function. To return information for all partitions of the owning object, specify NULL.

[ @data_compression= ] 'data_compression'

Is the type of compression to be evaluated. data_compression can be one of the following values: NONE, ROW, or PAGE.

0 (success) or 1 (failure)

The following result set is returned to provide current and estimated size for the table, index, or partition.

Column name

Data type

Description

object_name

sysname

Name of the table or the indexed view.

schema_name

sysname

Schema of the table or indexed view.

index_id

int

Index ID of an index:

0 = Heap

1 = Clustered index

> 1 = Nonclustered index

partition_number

int

Partition number. Returns 1 for a nonpartitioned table or index.

size_with_current_compression_setting (KB)

bigint

Size of the requested table, index, or partition as it currently exists.

size_with_requested_compression_setting (KB)

bigint

Estimated size of the table, index, or partition that uses the requested compression setting; and, if applicable, the existing fill factor, and assuming there is no fragmentation.

sample_size_with_current_compression_setting (KB)

bigint

Size of the sample with the current compression setting. This includes any fragmentation.

sample_size_with_requested_compression_setting (KB)

bigint

Size of the sample that is created by using the requested compression setting; and, if applicable, the existing fill factor and no fragmentation.

Use sp_estimate_data_compression_savings to estimate the savings that can occur when you enable a table or partition for row or page compression. For instance if the average size of the row can be reduced by 40 percent, you can potentially reduce the size of the object by 40 percent. You might not receive a space savings because this depends on the fill factor and the size of the row. For example, if you have a row that is 8000 bytes long and you reduce its size by 40 percent, you can still fit only one row on a data page. There is no savings.

If the results of running sp_estimate_data_compression_savings indicate that the table will grow, this means that many rows in the table use almost the whole precision of the data types, and the addition of the small overhead needed for the compressed format is more than the savings from compression. In this rare case, do not enable compression.

If a table is enabled for compression, use sp_estimate_data_compression_savings to estimate the average size of the row if the table is uncompressed.

An (IS) lock is acquired on the table during this operation. If an (IS) lock cannot be obtained, the procedure will be blocked. The table is scanned under the read committed isolation level.

If the requested compression setting is same as the current compression setting, the stored procedure will return the estimated size with no data fragmentation and using the existing fill factor.

If the index or partition ID does not exist, no results are returned.

Requires SELECT permission on the table.

The following example estimates the size of the Production.WorkOrderRouting table in the AdventureWorks2008R2 database if it is compressed by using ROW compression.

USE AdventureWorks2008R2;
GO
EXEC sp_estimate_data_compression_savings 'Production', 'WorkOrderRouting', NULL, NULL, 'ROW' ;
GO
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