sys.dm_db_index_physical_stats (Transact-SQL)

Artykuł
09/03/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

Returns size and fragmentation information for the data and indexes of the specified table or view in the SQL Server Database Engine. For an index, one row is returned for each level of the B-tree in each partition. For a heap, one row is returned for the IN_ROW_DATA allocation unit of each partition. For large object (LOB) data, one row is returned for the LOB_DATA allocation unit of each partition. If row-overflow data exists in the table, one row is returned for the ROW_OVERFLOW_DATA allocation unit in each partition.

Note

Documentation uses the term B-tree generally in reference to indexes. In rowstore indexes, the Database Engine implements a B+ tree. This does not apply to columnstore indexes or indexes on memory-optimized tables. For more information, see the SQL Server and Azure SQL index architecture and design guide.

sys.dm_db_index_physical_stats doesn't return information about memory-optimized indexes. For information about memory-optimized index use, see sys.dm_db_xtp_index_stats.

If you query sys.dm_db_index_physical_stats on a server instance that is hosting an availability group readable secondary replica, you might encounter a REDO blocking issue. This is because this dynamic management view acquires an Intent-Shared (IS) lock on the specified user table or view that can block requests by a REDO thread for an Exclusive (X) lock on that user table or view.

Transact-SQL syntax conventions

Syntax

sys.dm_db_index_physical_stats (
    { database_id | NULL | 0 | DEFAULT }
  , { object_id | NULL | 0 | DEFAULT }
  , { index_id | NULL | 0 | -1 | DEFAULT }
  , { partition_number | NULL | 0 | DEFAULT }
  , { mode | NULL | DEFAULT }
)

Arguments

database_id | NULL | 0 | DEFAULT

The ID of the database. database_id is smallint. Valid inputs are the ID of a database, NULL, 0, or DEFAULT. The default is 0. NULL, 0, and DEFAULT are equivalent values in this context.

Specify NULL to return information for all databases in the instance of SQL Server. If you specify NULL for database_id, you must also specify NULL for object_id, index_id, and partition_number.

The built-in function DB_ID can be specified. When you use DB_ID without specifying a database name, the compatibility level of the current database must be 90 or greater.

object_id | NULL | 0 | DEFAULT

The object ID of the table or view the index is on. object_id is int. Valid inputs are the ID of a table and view, NULL, 0, or DEFAULT. The default is 0. NULL, 0, and DEFAULT are equivalent values in this context.

In SQL Server 2016 (13.x) and later versions, valid inputs also include the service broker queue name or the queue internal table name. When default parameters are applied (that is, all objects, all indexes, etc.), fragmentation information for all queues is included in the result set.

Specify NULL to return information for all tables and views in the specified database. If you specify NULL for object_id, you must also specify NULL for index_id and partition_number.

index_id | 0 | NULL | -1 | DEFAULT

The ID of the index. index_id is int. Valid inputs are the ID of an index, 0 if object_id is a heap, NULL, -1, or DEFAULT. The default is -1. NULL, -1, and DEFAULT are equivalent values in this context.

Specify NULL to return information for all indexes for a base table or view. If you specify NULL for index_id, you must also specify NULL for partition_number.

partition_number | NULL | 0 | DEFAULT

The partition number in the object. partition_number is int. Valid inputs are the partition_number of an index or heap, NULL, 0, or DEFAULT. The default is 0. NULL, 0, and DEFAULT are equivalent values in this context.

Specify NULL to return information for all partitions of the owning object.

partition_number is 1-based. A nonpartitioned index or heap has partition_number set to 1.

mode | NULL | DEFAULT

The name of the mode. mode specifies the scan level that is used to obtain statistics. mode is sysname. Valid inputs are DEFAULT, NULL, LIMITED, SAMPLED, or DETAILED. The default (NULL) is LIMITED.

Table returned

Column name	Data type	Description
`database_id`	smallint	Database ID of the table or view. In Azure SQL Database, the values are unique within a single database or an elastic pool, but not within a logical server.
`object_id`	int	Object ID of the table or view that the index is on.
`index_id`	int	Index ID of an index. `0` = Heap.
`partition_number`	int	1-based partition number within the owning object; a table, view, or index. `1` = Nonpartitioned index or heap.
`index_type_desc`	nvarchar(60)	Description of the index type: - `HEAP` - `CLUSTERED INDEX` - `NONCLUSTERED INDEX` - `PRIMARY XML INDEX` - `EXTENDED INDEX` - `XML INDEX` - `COLUMNSTORE MAPPING INDEX` (internal) - `COLUMNSTORE DELETEBUFFER INDEX` (internal) - `COLUMNSTORE DELETEBITMAP INDEX` (internal)
`alloc_unit_type_desc`	nvarchar(60)	Description of the allocation unit type: - `IN_ROW_DATA` - `LOB_DATA` - `ROW_OVERFLOW_DATA` The `LOB_DATA` allocation unit contains the data that is stored in columns of type text, ntext, image, varchar(max), nvarchar(max), varbinary(max), and xml. For more information, see Data types. The `ROW_OVERFLOW_DATA` allocation unit contains the data that is stored in columns of type varchar(n), nvarchar(n), varbinary(n), and sql_variant that are pushed off-row.
`index_depth`	tinyint	Number of index levels. `1` = Heap, or `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation unit.
`index_level`	tinyint	Current level of the index. `0` for index leaf levels, heaps, and `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units. Greater than `0` for nonleaf index levels. index_level is the highest at the root level of an index. The nonleaf levels of indexes are only processed when mode is `DETAILED`.
`avg_fragmentation_in_percent`	float	Logical fragmentation for indexes, or extent fragmentation for heaps in the `IN_ROW_DATA` allocation unit. The value is measured as a percentage and takes into account multiple files. For definitions of logical and extent fragmentation, see Remarks. `0` for `LOB_DATA` and `ROW_OVERFLOW_DATA` allocation units. `NULL` for heaps when mode is `SAMPLED`.
`fragment_count`	bigint	Number of fragments in the leaf level of an `IN_ROW_DATA` allocation unit. For more information about fragments, see Remarks. `NULL` for nonleaf levels of an index, and `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units. `NULL` for heaps when mode is `SAMPLED`.
`avg_fragment_size_in_pages`	float	Average number of pages in one fragment in the leaf level of an `IN_ROW_DATA` allocation unit. `NULL` for nonleaf levels of an index, and `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units. `NULL` for heaps when mode is `SAMPLED`.
`page_count`	bigint	Total number of index or data pages. For an index, the total number of index pages in the current level of the B-tree in the `IN_ROW_DATA` allocation unit. For a heap, the total number of data pages in the `IN_ROW_DATA` allocation unit. For `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units, total number of pages in the allocation unit.
`avg_page_space_used_in_percent`	float	Average percentage of available data storage space used in all pages. For an index, average applies to the current level of the B-tree in the `IN_ROW_DATA` allocation unit. For a heap, the average of all data pages in the `IN_ROW_DATA` allocation unit. For `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units, the average of all pages in the allocation unit. `NULL` when mode is `LIMITED`.
`record_count`	bigint	Total number of records. For an index, total number of records applies to the current level of the B-tree in the `IN_ROW_DATA` allocation unit. For a heap, the total number of records in the `IN_ROW_DATA` allocation unit. Note: For a heap, the number of records returned from this function might not match the number of rows that are returned by running a `SELECT COUNT()` against the heap. This is because a row can contain multiple records. For example, under some update situations, a single heap row might have a forwarding record and a forwarded record as a result of the update operation. Also, most large LOB rows are split into multiple records in `LOB_DATA` storage. For `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units, the total number of records in the complete allocation unit. `NULL` when mode* is `LIMITED`.
`ghost_record_count`	bigint	Number of ghost records ready for removal by the ghost cleanup task in the allocation unit. `0` for nonleaf levels of an index in the `IN_ROW_DATA` allocation unit. `NULL` when mode is `LIMITED`.
`version_ghost_record_count`	bigint	Number of ghost records retained by an outstanding snapshot isolation transaction in an allocation unit. `0` for nonleaf levels of an index in the `IN_ROW_DATA` allocation unit. `NULL` when mode is `LIMITED`.
`min_record_size_in_bytes`	int	Minimum record size in bytes. For an index, minimum record size applies to the current level of the B-tree in the `IN_ROW_DATA` allocation unit. For a heap, the minimum record size in the `IN_ROW_DATA` allocation unit. For `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units, the minimum record size in the complete allocation unit. `NULL` when mode is `LIMITED`.
`max_record_size_in_bytes`	int	Maximum record size in bytes. For an index, the maximum record size applies to the current level of the B-tree in the `IN_ROW_DATA` allocation unit. For a heap, the maximum record size in the `IN_ROW_DATA` allocation unit. For `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units, the maximum record size in the complete allocation unit. `NULL` when mode is `LIMITED`.
`avg_record_size_in_bytes`	float	Average record size in bytes. For an index, the average record size applies to the current level of the B-tree in the `IN_ROW_DATA` allocation unit. For a heap, the average record size in the `IN_ROW_DATA` allocation unit. For `LOB_DATA` or `ROW_OVERFLOW_DATA` allocation units, the average record size in the complete allocation unit. `NULL` when mode is `LIMITED`.
`forwarded_record_count`	bigint	Number of records in a heap that have forward pointers to another data location. (This state occurs during an update, when there isn't enough room to store the new row in the original location.) `NULL` for any allocation unit other than the `IN_ROW_DATA` allocation units for a heap. `NULL` for heaps when mode is `LIMITED`.
`compressed_page_count`	bigint	The number of compressed pages. For heaps, newly allocated pages aren't `PAGE` compressed. A heap is `PAGE` compressed under two special conditions: when data is bulk imported or when a heap is rebuilt. Typical DML operations that cause page allocations aren't `PAGE` compressed. Rebuild a heap when the `compressed_page_count` value grows larger than the threshold you want. For tables that have a clustered index, the `compressed_page_count` value indicates the effectiveness of `PAGE` compression.
`hobt_id`	bigint	Heap or B-tree ID of the index or partition. For columnstore indexes, this is the ID for a rowset that tracks internal columnstore data for a partition. The rowsets are stored as data heaps or B-trees. They have the same index ID as the parent columnstore index. For more information, see sys.internal_partitions.
`columnstore_delete_buffer_state`	tinyint	`0` = `NOT_APPLICABLE` `1` = `OPEN` `2` = `DRAINING` `3` = `FLUSHING` `4` = `RETIRING` `5` = `READY` Applies to: SQL Server 2016 (13.x) and later versions, Azure SQL Database, and Azure SQL Managed Instance
`columnstore_delete_buffer_state_desc`	nvarchar(60)	`NOT VALID` - the parent index isn't a columnstore index. `OPEN` - deleters and scanners use this. `DRAINING` - deleters are draining out but scanners still use it. `FLUSHING` - buffer is closed and rows in the buffer are being written to the delete bitmap. `RETIRING` - rows in the closed delete buffer were written to the delete bitmap, but the buffer hasn't been truncated because scanners are still using it. New scanners don't need to use the retiring buffer because the open buffer is enough. `READY` - This delete buffer is ready for use. Applies to: SQL Server 2016 (13.x) and later versions, Azure SQL Database, and Azure SQL Managed Instance
`version_record_count`	bigint	This is the count of the row version records being maintained in this index. These row versions are maintained by the Accelerated database recovery feature. Applies to: SQL Server 2019 (15.x) and later versions, and Azure SQL Database
`inrow_version_record_count`	bigint	Count of ADR version records kept in the data row for fast retrieval. Applies to: SQL Server 2019 (15.x) and later versions, and Azure SQL Database
`inrow_diff_version_record_count`	bigint	Count of ADR version records kept in the form of differences from the base version. Applies to: SQL Server 2019 (15.x) and later versions, and Azure SQL Database
`total_inrow_version_payload_size_in_bytes`	bigint	Total size in bytes of the in-row version records for this index. Applies to: SQL Server 2019 (15.x) and later versions, and Azure SQL Database
`offrow_regular_version_record_count`	bigint	Count of version records being kept outside the original data row. Applies to: SQL Server 2019 (15.x) and later versions, and Azure SQL Database
`offrow_long_term_version_record_count`	bigint	Count of version records considered long term. Applies to: SQL Server 2019 (15.x) and later versions, and Azure SQL Database

Note

Remarks

The sys.dm_db_index_physical_stats dynamic management function replaces the DBCC SHOWCONTIG statement.

Scanning modes

The mode in which the function is executed determines the level of scanning performed to obtain the statistical data that is used by the function. mode is specified as LIMITED, SAMPLED, or DETAILED. The function traverses the page chains for the allocation units that make up the specified partitions of the table or index. sys.dm_db_index_physical_stats requires only an Intent-Shared (IS) table lock, regardless of the mode that it runs in.

The LIMITED mode is the fastest mode and scans the smallest number of pages. For an index, only the parent-level pages of the B-tree (that is, the pages above the leaf level) are scanned. For a heap, the associated PFS and IAM pages are examined and the data pages of a heap are scanned in LIMITED mode.

With LIMITED mode, compressed_page_count is NULL because the Database Engine only scans nonleaf pages of the B-tree and the IAM and PFS pages of the heap. Use SAMPLED mode to get an estimated value for compressed_page_count, and use DETAILED mode to get the actual value for compressed_page_count. The SAMPLED mode returns statistics based on a 1 percent sample of all the pages in the index or heap. Results in SAMPLED mode should be regarded as approximate. If the index or heap has fewer than 10,000 pages, DETAILED mode is used instead of SAMPLED.

The DETAILED mode scans all pages and returns all statistics.

The modes are progressively slower from LIMITED to DETAILED, because more work is performed in each mode. To quickly gauge the size or fragmentation level of a table or index, use the LIMITED mode. It's the fastest and doesn't return a row for each nonleaf level in the IN_ROW_DATA allocation unit of the index.

Use system functions to specify parameter values

You can use the Transact-SQL functions DB_ID and OBJECT_ID to specify a value for the database_id and object_id parameters. However, passing values that aren't valid to these functions can cause unintended results. For example, if the database or object name can't be found because they don't exist or are spelled incorrectly, both functions return NULL. The sys.dm_db_index_physical_stats function interprets NULL as a wildcard value specifying all databases or all objects.

Additionally, the OBJECT_ID function is processed before the sys.dm_db_index_physical_stats function is called and is therefore evaluated in the context of the current database, not the database specified in database_id. This behavior can cause the OBJECT_ID function to return a NULL value; or, if the object name exists in both the current database context and the specified database, an error message is returned. The following examples demonstrate these unintended results.

USE master;
GO
-- In this example, OBJECT_ID is evaluated in the context of the master database.
-- Because Person.Address does not exist in master, the function returns NULL.
-- When NULL is specified as an object_id, all objects in the database are returned.
-- The same results are returned when an object that is not valid is specified.
SELECT * FROM sys.dm_db_index_physical_stats
    (DB_ID(N'AdventureWorks2022'), OBJECT_ID(N'Person.Address'), NULL, NULL , 'DETAILED');
GO
-- This example demonstrates the results of specifying a valid object name
-- that exists in both the current database context and
-- in the database specified in the database_id parameter of the
-- sys.dm_db_index_physical_stats function.
-- An error is returned because the ID value returned by OBJECT_ID does not
-- match the ID value of the object in the specified database.
CREATE DATABASE Test;
GO
USE Test;
GO
CREATE SCHEMA Person;
GO
CREATE Table Person.Address(c1 int);
GO
USE AdventureWorks2022;
GO
SELECT * FROM sys.dm_db_index_physical_stats
    (DB_ID(N'Test'), OBJECT_ID(N'Person.Address'), NULL, NULL , 'DETAILED');
GO
-- Clean up temporary database.
DROP DATABASE Test;
GO

Best practice

Always make sure that a valid ID is returned when you use DB_ID or OBJECT_ID. For example, when you use OBJECT_ID, specify a three-part name such as OBJECT_ID(N'AdventureWorks2022.Person.Address'), or test the value returned by the functions before you use them in the sys.dm_db_index_physical_stats function. Examples A and B that follow demonstrate a safe way to specify database and object IDs.

Detect fragmentation

Fragmentation occurs through the process of data modifications (INSERT, UPDATE, and DELETE statements) that are made against the table and, therefore, to the indexes defined on the table. Because these modifications aren't ordinarily distributed equally among the rows of the table and indexes, the fullness of each page can vary over time. For queries that scan part or all of the indexes of a table, this kind of fragmentation can cause more page reads, which hinders parallel scanning of data.

The fragmentation level of an index or heap is shown in the avg_fragmentation_in_percent column. For heaps, the value represents the extent fragmentation of the heap. For indexes, the value represents the logical fragmentation of the index. Unlike DBCC SHOWCONTIG, the fragmentation calculation algorithms in both cases consider storage that spans multiple files and, therefore, are accurate.

Logical fragmentation

This is the percentage of out-of-order pages in the leaf pages of an index. An out-of-order page is a page for which the next physical page allocated to the index isn't the page pointed to by the next-page pointer in the current leaf page.

Extent fragmentation

This is the percentage of out-of-order extents in the leaf pages of a heap. An out-of-order extent is one for which the extent that contains the current page for a heap isn't physically the next extent after the extent that contains the previous page.

The value for avg_fragmentation_in_percent should be as close to zero as possible for maximum performance. However, values from 0 percent through 10 percent can be acceptable. All methods of reducing fragmentation, such as rebuilding, reorganizing, or recreating, can be used to reduce these values. For more information about how to analyze the degree of fragmentation in an index, see Optimize index maintenance to improve query performance and reduce resource consumption.

Reduce fragmentation in an index

When an index is fragmented in a way that the fragmentation is affecting query performance, there are three choices for reducing fragmentation:

Drop and recreate the clustered index.

Recreating a clustered index redistributes the data and results in full data pages. The level of fullness can be configured by using the FILLFACTOR option in CREATE INDEX. The drawbacks in this method are that the index is offline during the drop and recreate cycle, and that the operation is atomic. If the index creation is interrupted, the index isn't recreated. For more information, see CREATE INDEX.
Use ALTER INDEX REORGANIZE, the replacement for DBCC INDEXDEFRAG, to reorder the leaf level pages of the index in a logical order. Because this is an online operation, the index is available while the statement is running. The operation can also be interrupted without losing work already completed. The drawback in this method is that it doesn't do as good a job of reorganizing the data as an index rebuild operation, and it doesn't update statistics.
Use ALTER INDEX REBUILD, the replacement for DBCC DBREINDEX, to rebuild the index online or offline. For more information, see ALTER INDEX (Transact-SQL).

Fragmentation alone isn't a sufficient reason to reorganize or rebuild an index. The main effect of fragmentation is that it slows down page read-ahead throughput during index scans. This causes slower response times. If the query workload on a fragmented table or index doesn't involve scans, because the workload is primarily singleton lookups, removing fragmentation can have no effect.

Note

Running DBCC SHRINKFILE or DBCC SHRINKDATABASE can introduce fragmentation if an index is partly or completely moved during the shrink operation. Therefore, if a shrink operation must be performed, you should do it before fragmentation is removed.

Reduce fragmentation in a heap

To reduce the extent fragmentation of a heap, create a clustered index on the table and then drop the index. This redistributes the data while the clustered index is created. This also makes it as optimal as possible, considering the distribution of free space available in the database. When the clustered index is then dropped to recreate the heap, the data isn't moved and remains optimally in position. For information about how to perform these operations, see CREATE INDEX and DROP INDEX.

Caution

Creating and dropping a clustered index on a table, rebuilds all nonclustered indexes on that table twice.

Compact large object data

By default, the ALTER INDEX REORGANIZE statement compacts pages that contain large object (LOB) data. Because LOB pages aren't deallocated when empty, compacting this data can improve disk space use if lots of LOB data is deleted, or a LOB column is dropped.

Reorganizing a specified clustered index compacts all LOB columns that are contained in the clustered index. Reorganizing a nonclustered index compacts all LOB columns that are nonkey (included) columns in the index. When ALL is specified in the statement, all indexes that are associated with the specified table or view are reorganized. Additionally, all LOB columns that are associated with the clustered index, underlying table, or nonclustered index with included columns, are compacted.

Evaluate disk space use

The avg_page_space_used_in_percent column indicates page fullness. To achieve optimal disk space use, this value should be close to 100 percent for an index that doesn't have many random inserts. However, an index that has many random inserts and has very full pages have an increased number of page splits. This causes more fragmentation. Therefore, in order to reduce page splits, the value should be less than 100 percent. Rebuilding an index with the FILLFACTOR option specified allows the page fullness to be changed to fit the query pattern on the index. For more information about fill factor, see Specify Fill Factor for an Index. Also, ALTER INDEX REORGANIZE will compact an index by trying to fill pages to the FILLFACTOR that was last specified. This increases the value in avg_space_used_in_percent. ALTER INDEX REORGANIZE can't reduce page fullness. Instead, an index rebuild must be performed.

Evaluate index fragments

A fragment is made up of physically consecutive leaf pages in the same file for an allocation unit. An index has at least one fragment. The maximum fragments an index can have are equal to the number of pages in the leaf level of the index. Larger fragments mean that less disk I/O is required to read the same number of pages. Therefore, the larger the avg_fragment_size_in_pages value, the better the range scan performance. The avg_fragment_size_in_pages and avg_fragmentation_in_percent values are inversely proportional to each other. Therefore, rebuilding or reorganizing an index should reduce the amount of fragmentation and increase the fragment size.

Limitations

Doesn't return data for clustered columnstore indexes.

Permissions

Requires the following permissions:

CONTROL permission on the specified object within the database.
VIEW DATABASE STATE or VIEW DATABASE PERFORMANCE STATE (SQL Server 2022) permission to return information about all objects within the specified database, by using the object wildcard @object_id = NULL.
VIEW SERVER STATE or VIEW SERVER PERFORMANCE STATE (SQL Server 2022) permission to return information about all databases, by using the database wildcard @database_id = NULL.

Granting VIEW DATABASE STATE allows all objects in the database to be returned, regardless of any CONTROL permissions denied on specific objects.

Denying VIEW DATABASE STATE disallows all objects in the database to be returned, regardless of any CONTROL permissions granted on specific objects. Also, when the database wildcard @database_id = NULL is specified, the database is omitted.

For more information, see System dynamic management views.

Examples

The Transact-SQL code samples in this article use the AdventureWorks2022 or AdventureWorksDW2022 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

A. Return information about a specified table

The following example returns size and fragmentation statistics for all indexes and partitions of the Person.Address table. The scan mode is set to LIMITED for best performance and to limit the statistics that are returned. Executing this query requires, at a minimum, CONTROL permission on the Person.Address table.

DECLARE @db_id SMALLINT;
DECLARE @object_id INT;

SET @db_id = DB_ID(N'AdventureWorks2022');
SET @object_id = OBJECT_ID(N'AdventureWorks2022.Person.Address');

IF @db_id IS NULL
BEGIN;
    PRINT N'Invalid database';
END;
ELSE IF @object_id IS NULL
BEGIN;
    PRINT N'Invalid object';
END;
ELSE
BEGIN;
    SELECT * FROM sys.dm_db_index_physical_stats(@db_id, @object_id, NULL, NULL , 'LIMITED');
END;
GO

B. Return information about a heap

The following example returns all statistics for the heap dbo.DatabaseLog in the AdventureWorks2022 database. Because the table contains LOB data, a row is returned for the LOB_DATA allocation unit in addition to the row returned for the IN_ROW_ALLOCATION_UNIT that is storing the data pages of the heap. Executing this query requires, at a minimum, CONTROL permission on the dbo.DatabaseLog table.

DECLARE @db_id SMALLINT;
DECLARE @object_id INT;
SET @db_id = DB_ID(N'AdventureWorks2022');
SET @object_id = OBJECT_ID(N'AdventureWorks2022.dbo.DatabaseLog');
IF @object_id IS NULL
BEGIN;
    PRINT N'Invalid object';
END;
ELSE
BEGIN;
    SELECT * FROM sys.dm_db_index_physical_stats(@db_id, @object_id, 0, NULL , 'DETAILED');
END;
GO

C. Return information for all databases

The following example returns all statistics for all tables and indexes within the instance of SQL Server by specifying the wildcard NULL for all parameters. Executing this query requires the VIEW SERVER STATE permission.

SELECT * FROM sys.dm_db_index_physical_stats (NULL, NULL, NULL, NULL, NULL);
GO

D. Use sys.dm_db_index_physical_stats in a script to rebuild or reorganize indexes

The following example automatically reorganizes or rebuilds all partitions in a database that have an average fragmentation over 10 percent. Executing this query requires the VIEW DATABASE STATE permission. This example specifies DB_ID as the first parameter without specifying a database name.

-- Ensure a USE <databasename> statement has been executed first.
SET NOCOUNT ON;

DECLARE @objectid INT;
DECLARE @indexid INT;
DECLARE @partitioncount BIGINT;
DECLARE @schemaname NVARCHAR(130);
DECLARE @objectname NVARCHAR(130);
DECLARE @indexname NVARCHAR(130);
DECLARE @partitionnum BIGINT;
DECLARE @partitions BIGINT;
DECLARE @frag FLOAT;
DECLARE @command NVARCHAR(4000);

-- Conditionally select tables and indexes from the sys.dm_db_index_physical_stats function
-- and convert object and index IDs to names.
SELECT object_id AS objectid,
    index_id AS indexid,
    partition_number AS partitionnum,
    avg_fragmentation_in_percent AS frag
INTO #work_to_do
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, 'LIMITED')
WHERE avg_fragmentation_in_percent > 10.0
    AND index_id > 0;

-- Declare the cursor for the list of partitions to be processed.
DECLARE partitions CURSOR
FOR
SELECT *
FROM #work_to_do;

-- Open the cursor.
OPEN partitions;

-- Loop through the partitions.
WHILE (1 = 1)
BEGIN;

    FETCH NEXT
    FROM partitions
    INTO @objectid,
        @indexid,
        @partitionnum,
        @frag;

    IF @@FETCH_STATUS < 0
        BREAK;

    SELECT @objectname = QUOTENAME(o.name),
        @schemaname = QUOTENAME(s.name)
    FROM sys.objects AS o
    INNER JOIN sys.schemas AS s
        ON s.schema_id = o.schema_id
    WHERE o.object_id = @objectid;

    SELECT @indexname = QUOTENAME(name)
    FROM sys.indexes
    WHERE object_id = @objectid
        AND index_id = @indexid;

    SELECT @partitioncount = count(*)
    FROM sys.partitions
    WHERE object_id = @objectid
        AND index_id = @indexid;

    -- 30 is an arbitrary decision point at which to switch between reorganizing and rebuilding.
    IF @frag < 30.0
        SET @command = N'ALTER INDEX ' + @indexname + N' ON ' + @schemaname + N'.' + @objectname + N' REORGANIZE';

    IF @frag >= 30.0
        SET @command = N'ALTER INDEX ' + @indexname + N' ON ' + @schemaname + N'.' + @objectname + N' REBUILD';

    IF @partitioncount > 1
        SET @command = @command + N' PARTITION=' + CAST(@partitionnum AS NVARCHAR(10));

    EXEC (@command);

    PRINT N'Executed: ' + @command;
END;

-- Close and deallocate the cursor.
CLOSE partitions;

DEALLOCATE partitions;

-- Drop the temporary table.
DROP TABLE #work_to_do;
GO

E. Use sys.dm_db_index_physical_stats to show the number of page-compressed pages

The following example shows how to display and compare the total number of pages against the pages that are row and page compressed. This information can be used to determine the benefit that compression is providing for an index or table.

SELECT o.name,
    ips.partition_number,
    ips.index_type_desc,
    ips.record_count,
    ips.avg_record_size_in_bytes,
    ips.min_record_size_in_bytes,
    ips.max_record_size_in_bytes,
    ips.page_count,
    ips.compressed_page_count
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, 'DETAILED') ips
INNER JOIN sys.objects o
    ON o.object_id = ips.object_id
ORDER BY record_count DESC;

F. Use sys.dm_db_index_physical_stats in SAMPLED mode

The following example shows how SAMPLED mode returns an approximate that is different than the DETAILED mode results.

CREATE TABLE t3 (
    col1 INT PRIMARY KEY,
    col2 VARCHAR(500)
    )
    WITH (DATA_COMPRESSION = PAGE);
GO

BEGIN TRANSACTION

DECLARE @idx INT = 0;

WHILE @idx < 1000000
BEGIN
    INSERT INTO t3 (col1, col2)
    VALUES (
        @idx,
        REPLICATE('a', 100) + CAST(@idx AS VARCHAR(10)) + REPLICATE('a', 380)
        )

    SET @idx = @idx + 1
END

COMMIT;
GO

SELECT page_count,
    compressed_page_count,
    forwarded_record_count,
    *
FROM sys.dm_db_index_physical_stats(db_id(), object_id('t3'), NULL, NULL, 'SAMPLED');

SELECT page_count,
    compressed_page_count,
    forwarded_record_count,
    *
FROM sys.dm_db_index_physical_stats(db_id(), object_id('t3'), NULL, NULL, 'DETAILED');

G. Query service broker queues for index fragmentation

Applies to: SQL Server 2016 (13.x) and later versions

The following example shows how to query server broker queues for fragmentation.

--Using queue internal table name
SELECT *
FROM sys.dm_db_index_physical_stats(db_id(), object_id('sys.queue_messages_549576996'), DEFAULT, DEFAULT, DEFAULT);

--Using queue name directly
SELECT *
FROM sys.dm_db_index_physical_stats(db_id(), object_id('ExpenseQueue'), DEFAULT, DEFAULT, DEFAULT);

Udostępnij za pośrednictwem

sys.dm_db_index_physical_stats (Transact-SQL)

Syntax

Arguments

database_id | NULL | 0 | DEFAULT

object_id | NULL | 0 | DEFAULT

index_id | 0 | NULL | -1 | DEFAULT

partition_number | NULL | 0 | DEFAULT

mode | NULL | DEFAULT

Table returned

Remarks

Scanning modes

Use system functions to specify parameter values

Best practice

Detect fragmentation

Logical fragmentation

Extent fragmentation

Reduce fragmentation in an index

Reduce fragmentation in a heap

Compact large object data

Evaluate disk space use

Evaluate index fragments

Limitations

Permissions

Examples

A. Return information about a specified table

B. Return information about a heap

C. Return information for all databases

D. Use sys.dm_db_index_physical_stats in a script to rebuild or reorganize indexes

E. Use sys.dm_db_index_physical_stats to show the number of page-compressed pages

F. Use sys.dm_db_index_physical_stats in SAMPLED mode

G. Query service broker queues for index fragmentation

Opinia

Dodatkowe zasoby

Udostępnij za pośrednictwem

sys.dm_db_index_physical_stats (Transact-SQL)

Syntax

Arguments

database_id | NULL | 0 | DEFAULT

object_id | NULL | 0 | DEFAULT

index_id | 0 | NULL | -1 | DEFAULT

partition_number | NULL | 0 | DEFAULT

mode | NULL | DEFAULT

Table returned

Remarks

Scanning modes

Use system functions to specify parameter values

Best practice

Detect fragmentation

Logical fragmentation

Extent fragmentation

Reduce fragmentation in an index

Reduce fragmentation in a heap

Compact large object data

Evaluate disk space use

Evaluate index fragments

Limitations

Permissions

Examples

A. Return information about a specified table

B. Return information about a heap

C. Return information for all databases

D. Use sys.dm_db_index_physical_stats in a script to rebuild or reorganize indexes

E. Use sys.dm_db_index_physical_stats to show the number of page-compressed pages

F. Use sys.dm_db_index_physical_stats in SAMPLED mode

G. Query service broker queues for index fragmentation

Related content

Opinia

Dodatkowe zasoby