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sys.memory_optimized_tables_internal_attributes (Transact-SQL)

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Applies to: SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance

Contains a row for each internal memory-optimized table used for storing user memory-optimized tables. Each user table corresponds to one or more internal tables. A single table is used for the core data storage. Additional internal tables are used to support features such as temporal, columnstore index and off-row (LOB) storage for memory-optimized tables.

Column name Data type Description
object_id int ID of the user table. Internal memory-optimized tables that exist to support a user table (such as off-row storage or deleted rows in case of Hk/Columnstore combinations) have the same object_id as their parent.
xtp_object_id bigint In-Memory OLTP object ID corresponding to the internal memory-optimized table that is used to support the user table. It is unique within the database and it can change over the lifetime of the object.
type int Type of internal table.

0 => DELETED_ROWS_TABLE
1 => USER_TABLE
2 => DICTIONARIES_TABLE
3 => SEGMENTS_TABLE
4 => ROW_GROUPS_INFO_TABLE
5 => INTERNAL OFF-ROW DATA TABLE
252 => INTERNAL_TEMPORAL_HISTORY_TABLE
type_desc nvarchar(60) Description of the type

DELETED_ROWS_TABLE -> Internal table tracking deleted rows for a columnstore index
USER_TABLE -> Table containing the in-row user data
DICTIONARIES_TABLE -> Dictionaries for a columnstore index
SEGMENTS_TABLE -> Compressed segments for a columnstore index
ROW_GROUPS_INFO_TABLE -> Metadata about compressed row groups of a columnstore index
INTERNAL OFF-ROW DATA TABLE -> Internal table used for storage of an off-row column. In this case, minor_id reflects the column_id.
INTERNAL_TEMPORAL_HISTORY_TABLE -> Hot tail of the disk-based history table. Rows inserted into the history are inserted into this internal memory-optimized table first. There is a background task that asynchronously moves rows from this internal table to the disk-based history table.
minor_id int 0 indicates a user or internal table

Non-0 indicates the ID of a column stored off-row. Joins with column_id in sys.columns.

Each column stored off-row has a corresponding row in this system view.

Permissions

The visibility of the metadata in catalog views is limited to securables that a user either owns, or on which the user was granted some permission. For more information, see Metadata Visibility Configuration.

Examples

A. Returning all columns that are stored off-row

The following T-SQL script illustrates a table with multiple large non-LOB columns and a single LOB column:

CREATE TABLE dbo.LargeTableSample
(
      Id   int IDENTITY PRIMARY KEY NONCLUSTERED,
      C1   nvarchar(4000),
      C2   nvarchar(4000),
      C3   nvarchar(4000),
      C4   nvarchar(4000),
      Misc nvarchar(max)
) WITH (MEMORY_OPTIMIZED = ON);
GO

The following query shows all columns that are stored off-row, along with their sizes. A size of -1 indicates a LOB column. All LOB columns are stored off-row.

SELECT 
  QUOTENAME(SCHEMA_NAME(o.schema_id)) + N'.' + QUOTENAME(OBJECT_NAME(moa.object_id)) AS 'table', 
  c.name AS 'column', 
  c.max_length
FROM sys.memory_optimized_tables_internal_attributes moa
     JOIN sys.columns c ON moa.object_id = c.object_id AND moa.minor_id=c.column_id
     JOIN sys.objects o on moa.object_id=o.object_id 
WHERE moa.type=5;

B. Returning memory consumption of all columns that are stored off-row

To get more details about the memory consumption of off-row columns you can use the following query, which shows the memory consumption of all internal tables and their indexes that are used to store the off-row columns:

SELECT
  QUOTENAME(SCHEMA_NAME(o.schema_id)) + N'.' + QUOTENAME(OBJECT_NAME(moa.object_id)) AS 'table',
  c.name AS 'column',
  c.max_length,
  mc.memory_consumer_desc,
  mc.index_id,
  mc.allocated_bytes,
  mc.used_bytes
FROM sys.memory_optimized_tables_internal_attributes moa
   JOIN sys.columns c ON moa.object_id = c.object_id AND moa.minor_id=c.column_id
   JOIN sys.dm_db_xtp_memory_consumers mc ON moa.xtp_object_id=mc.xtp_object_id
   JOIN sys.objects o on moa.object_id=o.object_id 
WHERE moa.type=5;

C. Returning memory consumption of columnstore indexes on memory-optimized tables

Use the following query to show the memory consumption of columnstore indexes on memory-optimized tables:

SELECT
  QUOTENAME(SCHEMA_NAME(o.schema_id)) + N'.' + QUOTENAME(OBJECT_NAME(moa.object_id)) AS 'table',
  i.name AS 'columnstore index',
  SUM(mc.allocated_bytes) / 1024 as [allocated_kb],
  SUM(mc.used_bytes) / 1024 as [used_kb]
FROM sys.memory_optimized_tables_internal_attributes moa
   JOIN sys.indexes i ON moa.object_id = i.object_id AND i.type in (5,6)
   JOIN sys.dm_db_xtp_memory_consumers mc ON moa.xtp_object_id=mc.xtp_object_id
   JOIN sys.objects o on moa.object_id=o.object_id
WHERE moa.type IN (0, 2, 3, 4)
GROUP BY o.schema_id, moa.object_id, i.name;

Use the following query break down the memory consumption across internal structures used for columnstore indexes on memory-optimized tables:

SELECT
  QUOTENAME(SCHEMA_NAME(o.schema_id)) + N'.' + QUOTENAME(OBJECT_NAME(moa.object_id)) AS 'table',
  i.name AS 'columnstore index',
  moa.type_desc AS 'internal table',
  mc.index_id AS 'index',
  mc.memory_consumer_desc,
  mc.allocated_bytes / 1024 as [allocated_kb],
  mc.used_bytes / 1024 as [used_kb]
FROM sys.memory_optimized_tables_internal_attributes moa
   JOIN sys.indexes i ON moa.object_id = i.object_id AND i.type in (5,6)
   JOIN sys.dm_db_xtp_memory_consumers mc ON moa.xtp_object_id=mc.xtp_object_id
   JOIN sys.objects o on moa.object_id=o.object_id
WHERE moa.type IN (0, 2, 3, 4)