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sys.dm_db_missing_index_group_stats

Updated: April 2, 2011

This topic is OBSOLETE. You can find the most current version in the SQL 14 Transact-SQL Reference.

ImportantImportant
This topic is not maintained. For the current version, see sys.dm_db_missing_index_group_stats.

Returns summary information about groups of missing indexes, excluding spatial indexes.

In Microsoft Azure SQL Database, dynamic management views cannot expose information that would impact database containment or expose information about other databases the user has access to. To avoid exposing this information, every row that contains data that doesn’t belong to the connected tenant is filtered out.

 

Column name Data type Description

group_handle

int

Identifies a group of missing indexes. This identifier is unique across the server.

The other columns provide information about all queries for which the index in the group is considered missing.

An index group contains only one index.

unique_compiles

bigint

Number of compilations and recompilations that would benefit from this missing index group. Compilations and recompilations of many different queries can contribute to this column value.

user_seeks

bigint

Number of seeks caused by user queries that the recommended index in the group could have been used for.

user_scans

bigint

Number of scans caused by user queries that the recommended index in the group could have been used for.

last_user_seek

datetime

Date and time of last seek caused by user queries that the recommended index in the group could have been used for.

last_user_scan

datetime

Date and time of last scan caused by user queries that the recommended index in the group could have been used for.

avg_total_user_cost

float

Average cost of the user queries that could be reduced by the index in the group.

avg_user_impact

float

Average percentage benefit that user queries could experience if this missing index group was implemented. The value means that the query cost would on average drop by this percentage if this missing index group was implemented.

system_seeks

bigint

Number of seeks caused by system queries, such as auto stats queries, that the recommended index in the group could have been used for. For more information, see Auto Stats Event Class.

system_scans

bigint

Number of scans caused by system queries that the recommended index in the group could have been used for.

last_system_seek

datetime

Date and time of last system seek caused by system queries that the recommended index in the group could have been used for.

last_system_scan

datetime

Date and time of last system scan caused by system queries that the recommended index in the group could have been used for.

avg_total_system_cost

float

Average cost of the system queries that could be reduced by the index in the group.

avg_system_impact

float

Average percentage benefit that system queries could experience if this missing index group was implemented. The value means that the query cost would on average drop by this percentage if this missing index group was implemented.

Information returned by sys.dm_db_missing_index_group_stats is updated by every query execution, not by every query compilation or recompilation. Usage statistics are not persisted and are kept only until SQL Server is restarted. Database administrators should periodically make backup copies of the missing index information if they want to keep the usage statistics after server recycling.

Requires VIEW DATABASE STATE permission on server. Cannot be queried from the master database. For more information, see Dynamic Management Objects.

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