1. Statistics for beginners – In-Memory OLTP
Lies, a blatant lie, statistics. Demystification of the statistics.
In-Memory OLTP
Андрій Зробок

2. Database creation USE [master] GO
/****** Object: Database [IMstat] Script Date: 3/4/2015 3:58:01 PM ******/
CREATE DATABASE [IMstat]
CONTAINMENT = NONE
ON PRIMARY
( NAME = N'IMstat', FILENAME = N'D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER2014\MSSQL\DATA\IMstat.mdf' , SIZE = 5120KB , MAXSIZE = UNLIMITED, FILEGROWTH = 1024KB )
LOG ON
( NAME = N'IMstat_log', FILENAME = N'D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER2014\MSSQL\DATA\IMstat_log.ldf' , SIZE = 2048KB , MAXSIZE = 2048GB , FILEGROWTH = 10%)
ALTER DATABASE [IMstat] SET COMPATIBILITY_LEVEL = 120
-- enable for in-memory OLTP - change file path as needed
ALTER DATABASE IMstat ADD FILEGROUP IMstat_memory CONTAINS MEMORY_OPTIMIZED_DATA GO
ALTER DATABASE IMstat ADD FILE (name='IMstat_memory1', filename='D:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER2014\MSSQL\DATA\IMstat_memory1.mdf') TO FILEGROUP IMstat_memory
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3. Database creation
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4. Table creation
-- non-clustered hash (equal operation)
CREATE TABLE [dbo].[TransactionHistory](
[TransactionID] [int] NOT NULL primary key
nonclustered hash with (bucket_count= ),
[ProductID] [int] NOT NULL index ix_ProductId
nonclustered hash with (bucket_count=1000),
[ReferenceOrderID] [int] NOT NULL,
[ReferenceOrderLineID] [int] NOT NULL ,
[TransactionDate] [datetime] NOT NULL ,
[TransactionType] [nchar](1) NOT NULL,
[Quantity] [int] NOT NULL,
[ActualCost] [money] NOT NULL,
[ModifiedDate] [datetime] NOT NULL)
WITH (MEMORY_OPTIMIZED=ON) GO
-- auto-generated script
CREATE TABLE [dbo].[TransactionHistory] (
[TransactionID] [int] NOT NULL,
[ProductID] [int] NOT NULL
[ReferenceOrderID] [int] NOT NULL,
[ReferenceOrderLineID] [int] ,NOT NULL,
[TransactionDate] [datetime] NOT NULL,
[TransactionType] [nchar](1) COLLATE Latin1_General_CI_AS NOT NULL,
[Quantity] [int] NOT NULL,
[ActualCost] [money] NOT NULL,
[ModifiedDate] [datetime] NOT NULL,
INDEX [ix_ProductId] NONCLUSTERED HASH
([ProductID])WITH ( BUCKET_COUNT = 1024),
PRIMARY KEY NONCLUSTERED HASH
([TransactionID])WITH ( BUCKET_COUNT = )
)WITH ( MEMORY_OPTIMIZED = ON , DURABILITY = SCHEMA_AND_DATA ) GO
-- non-clustered b-tree (aggregation/diapason
-- operation)
CREATE TABLE [dbo].[TransactionHistory_1](
[TransactionID] [int] NOT NULL primary key
nonclustered hash with (bucket_count= ),
[ProductID] [int] NOT NULL index ix_ProductId
nonclustered ,
[ReferenceOrderID] [int] NOT NULL,
[ReferenceOrderLineID] [int] NOT NULL ,
[TransactionDate] [datetime] NOT NULL ,
[TransactionType] [nchar](1) NOT NULL,
[Quantity] [int] NOT NULL,
[ActualCost] [money] NOT NULL,
[ModifiedDate] [datetime] NOT NULL )
WITH (MEMORY_OPTIMIZED=ON) GO
A memory-optimized table can have up to 8 indexes, including the index created with the primary key.
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5. Btw. Tables: Disk based VS in-memory
Disk primary, memory secondary
-“live” on disk
- Data save as page (8k)
- Buffer pull has the same structure (mirror of disk)
- Blocking for logical data protection
- Latches, spinlock for memory protection (waits)
Memory primary, disk secondary
- “live” in memory
- Data save as linked list (one index required) of records
- Saved on disk as file stream
- No blocking (versioning)
- No latches, no spinlock
- No waits
Must be loaded into memory
Can be saved on the disk
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6. Btw. Tables: Disk based VS in-memory
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7. Data loading -- Productid - b-tree index
USE [IMstat] GO
SELECT [TransactionID]
,[ProductID]
,[ReferenceOrderID]
,[ReferenceOrderLineID]
,[TransactionDate]
,[TransactionType]
,[Quantity]
,[ActualCost]
,[ModifiedDate]
into #t1
FROM [AdventureWorks2014].[Production].[TransactionHistory]
-- ProductID – hash index
INSERT INTO [dbo].[TransactionHistory]
([TransactionID]
,[ProductID]
,[ReferenceOrderID]
,[ReferenceOrderLineID]
,[TransactionDate]
,[TransactionType]
,[Quantity]
,[ActualCost]
,[ModifiedDate])
SELECT [TransactionID]
,[ModifiedDate]
FROM #t1
-- Productid - b-tree index
insert into [dbo].[TransactionHistory_1]
select * from [dbo].[TransactionHistory] go
Msg 41317, Level 16accesses memory optimized tables or natively compiled proc, State 5, Line 4
A user transaction that edures cannot access more than one user database or databases model and msdb, and it cannot write to master.
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8. Default Statistics
select * from [dbo].[TransactionHistory] where productid = 324 go
-- SQL Server assumes that the table will have a number of rows equal to the number of buckets on the index
-- No auto update statistics
DBCC SHOW_STATISTICS ('[dbo].[TransactionHistory]', ix_ProductID) WITH STAT_HEADER go
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9. Update Statistics 9 | 1/14/2019 | Statistics for beginners - 2
UPDATE STATISTICS [dbo].[TransactionHistory] WITH FULLSCAN, NORECOMPUTE
-- fullscan - Memory-Optimized tables don't support sampled statistics
-- norecompute - Memory-Optimized tables do not automatically update statistics
DBCC SHOW_STATISTICS ('[dbo].[TransactionHistory]', ix_ProductID)
dbcc freeproccache go
select * from [dbo].[TransactionHistory]
where productid = 321
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10. Aggregation (hash vs b-tree)
dbcc freeproccache go
select productid, count(*) from [dbo].[TransactionHistory] where productid between 802 and 850 group by productid
select productid, count(*) from [dbo].[TransactionHistory_1] where productid between 802 and 850 group by productid
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11. Diapason (hash vs b-tree)
dbcc freeproccache go
select * from [dbo].[TransactionHistory]
where productid between 802 and 850
select * from [dbo].[TransactionHistory_1]
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12. Without index: does not created > does not used?
-- non indexed column
CREATE STATISTICS sta_referenceorderid
ON [dbo].[TransactionHistory_1] (referenceorderid) WITH FULLSCAN, NORECOMPUTE
-- disk based table (without any indexes and constraints)
select * into dbo.transactionhistory_2
from [AdventureWorks2014].production.transactionhistory
dbcc freeproccache
dbcc DROPCLEANBUFFERS
set statistics time on go
-- in memory OLTP table
print 'in-memory'
select productid, count(*) from dbo.transactionhistory_1 where ReferenceOrderID = group by productid
-- disk based table
print 'disc based'
select productid, count(*) from dbo.transactionhistory_2 where ReferenceOrderID = group by productid
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13. Without index: does not created > does not used?
DBCC execution completed. If DBCC printed error messages, contact your system administrator.
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 2 ms.
in-memory
SQL Server Execution Times: CPU time = 0 ms, elapsed time = 0 ms.
(72 row(s) affected)
(1 row(s) affected)
SQL Server Execution Times: CPU time = 31 ms, elapsed time = 70 ms.
disc based
SQL Server Execution Times: CPU time = 0 ms, elapsed time = 61 ms.
SQL Server parse and compile time: CPU time = 0 ms, elapsed time = 0 ms.
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14. Without index: does not created > does not used?
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15. Natively Compiled Stored Procedures
CREATE PROCEDURE dbo.get_transactionHistory (
@productid int )
WITH NATIVE_COMPILATION, SCHEMABINDING, EXECUTE AS OWNER AS
BEGIN ATOMIC
WITH (TRANSACTION ISOLATION LEVEL = SNAPSHOT, LANGUAGE = N'us_english')
SELECT
transactionID, transactiondate, transactiontype, quantity, actualcost
FROM [dbo].[TransactionHistory]
WHERE productid
END GO
Natively Compiled Stored Procedures do not use the plan cache. The query plan is made at compile time when the procedure's DLL is created. So to use a new plan on a natively compiled stored procedure you must drop and recreate the natively compiled stored procedure in question.
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16. Natively Compiled Stored Procedures
SET SHOWPLAN_XML ON GO
exec dbo.get_transactionHistory 321 go
SET SHOWPLAN_XML OFF
Nested Loops is the only join operator supported in natively compiled stored procedures. All plans that contain joins will use the Nested Loops operator, even if the plan for same query executed as interpreted Transact-SQL contains a hash or merge join.
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17. Guidelines for Statistics
To ensure that the query optimizer has up-to-date statistics when creating query plans, deploy memory-optimized tables using these five steps:
Create tables and indexes. Indexes are specified inline in the CREATE TABLE statements.
Load data into the tables.
Update statistics on the tables.
Create stored procedures that access the tables.
Run the workload, which can contain a mix of natively compiled and interpreted Transact-SQL stored procedures, as well as ad hoc batches.
Creating natively compiled stored procedures after you load the data and update the statistics ensures that the optimizer has statistics available for the memory-optimized tables. This will ensure efficient query plans when the procedure is compiled.
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18. Statistics for beginners – in-Memory OLTP
Performance depends on correct index type but not up-to-date statistics
Statistics on non-indexed column does not matter
Q&A
The end
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