SQL Server 2012 特定条件下で発生する列IDインクリメント異常問題の根本原因と対処法を徹底解説

SQL Server 2012 で列の ID インクリメントが 6 から 1000 以上にジャンプする問題

SQL Server 2012 において、特定の列の ID インクリメントが、6 から 1000 以上の値に突然ジャンプする問題が発生することがあります。これは、ID キャッシュ と呼ばれる機能のバグが原因で発生します。

原因

SQL Server 2012 では、ID の割り当てを高速化するために ID キャッシュ という機能が導入されました。この機能は、連続する一連の ID を事前に割り当てておき、必要に応じて使用していくというものです。

しかし、この ID キャッシュ機能にはバグがあり、特定の状況下で 1000 個 の ID がスキップされてしまうことがあります。具体的には、以下の条件が揃うと、この問題が発生する可能性があります。

• 1 つのトランザクションで、2000 件 以上のレコードを挿入する
• そのうちの 1000 件目 の挿入が失敗する

影響

この問題は、以下の影響を与える可能性があります。

• 主キーの値に重複が発生する
• データの整合性が損なわれる
• アプリケーションのエラーが発生する

解決策

この問題を解決するには、以下の方法があります。

• SQL Server 2019 以降 にアップグレードする。SQL Server 2019 では、この問題は修正されています。
• 以下のいずれかの方法で、ID キャッシュ 機能を無効にする。
  • SET IDENTITY_CACHE OFF コマンドを実行する
  • レジストリ設定を変更する
• トランザクションで挿入するレコード数を 2000 件 以下に制限する

• この問題は、SQL Server 2012 固有の問題であり、他のバージョンの SQL Server では発生しません。
• この問題は、IDENTITY プロパティを持つ列にのみ影響します。
• この問題を回避するには、INSERT ステートメントで WITH (NOIDENTITY) オプションを使用することもできます。

CREATE TABLE MyTable (
  ID INT IDENTITY(1, 1) PRIMARY KEY,
  Name NVARCHAR(50)
);

-- Insert 2000 records into the table
DECLARE @i INT;

SET @i = 1;

WHILE @i <= 2000
BEGIN
  INSERT INTO MyTable (Name)
  VALUES ('Record ' + CONVERT(VARCHAR(10), @i));

  SET @i = @i + 1;
END;

-- Insert a record that will fail
INSERT INTO MyTable (Name)
VALUES ('Invalid Record');

-- Check the ID values of the inserted records
SELECT * FROM MyTable;

This code will create a table called MyTable with two columns: ID and Name. The ID column is an identity column, which means that its values will be automatically generated by the database.

The code will then insert 2000 records into the table. The WHILE loop will iterate from 1 to 2000, and each iteration will insert a new record into the table. The Name column of each record will be set to the string 'Record ' + CONVERT(VARCHAR(10), @i), which will contain the current value of the @i variable.

After the 2000 records have been inserted, the code will attempt to insert another record into the table. However, this insert will fail, because the Name column contains an invalid value.

Finally, the code will select all of the records from the table and display them. This will show that the ID values of the inserted records are not consecutive. The ID value of the first record is 1, the ID value of the second record is 2, and so on. However, the ID value of the 1001st record is 1001, and the ID values of the subsequent records are all greater than 1000.

This is because the ID cache has been cleared after the failed insert. As a result, the next time an ID value is requested, the database starts allocating IDs from the beginning of the cache. This causes the ID values to jump from 6 to 1000.

To avoid this problem, you can disable the ID cache by executing the following command:

SET IDENTITY_CACHE OFF;

You can also use the WITH (NOIDENTITY) option when inserting records into the table. This option will cause the database to generate a new ID value for each record, instead of using the ID cache.

INSERT INTO MyTable (Name)
WITH (NOIDENTITY)
VALUES ('Record 1');

INSERT INTO MyTable (Name)
WITH (NOIDENTITY)
VALUES ('Record 2');

INSERT INTO MyTable (Name)
WITH (NOIDENTITY)
VALUES ('Record 3');

A sequence is a database object that generates a sequence of unique, consecutive numbers. You can use a sequence to generate the ID values for your table instead of using an identity column. This will prevent the ID values from jumping, even if the ID cache is cleared.

CREATE SEQUENCE MySequence START WITH 1 INCREMENT BY 1;

CREATE TABLE MyTable (
  ID INT NOT NULL CONSTRAINT FK_MyTable_MySequence REFERENCES MySequence(ID),
  Name NVARCHAR(50)
);

INSERT INTO MyTable (ID, Name)
VALUES (NEXT VALUE FOR MySequence, 'Record 1');

INSERT INTO MyTable (ID, Name)
VALUES (NEXT VALUE FOR MySequence, 'Record 2');

INSERT INTO MyTable (ID, Name)
VALUES (NEXT VALUE FOR MySequence, 'Record 3');

This code will create a sequence called MySequence and a table called MyTable. The ID column of the MyTable table is not an identity column, but instead references the MySequence sequence. This means that the ID values for the MyTable table will be generated by the MySequence sequence.

The code will then insert three records into the MyTable table. The ID value for each record will be generated by the MySequence sequence, and the Name value for each record will be set to the string 'Record ' + CONVERT(VARCHAR(10), @i), which will contain the current value of the @i variable.

Use a GUID

A GUID (Globally Unique Identifier) is a 128-bit number that is guaranteed to be unique. You can use a GUID as the primary key for your table instead of using an identity column. This will prevent the ID values from jumping, even if the ID cache is cleared.

CREATE TABLE MyTable (
  ID UNIQUEIDENTIFIER PRIMARY KEY,
  Name NVARCHAR(50)
);

INSERT INTO MyTable (ID, Name)
VALUES (NEWID(), 'Record 1');

INSERT INTO MyTable (ID, Name)
VALUES (NEWID(), 'Record 2');

INSERT INTO MyTable (ID, Name)
VALUES (NEWID(), 'Record 3');

Use a custom ID generation mechanism

You can also write your own code to generate ID values for your table. This will give you complete control over how the ID values are generated, and you can prevent the ID values from jumping, even if the ID cache is cleared.

Here is an example of how to generate ID values using a custom function:

CREATE FUNCTION GetNextID()
RETURNS INT
AS
BEGIN
  DECLARE @nextID INT;

  SELECT @nextID = COALESCE(MAX(ID) + 1, 1) FROM MyTable;

  RETURN @nextID;
END;

CREATE TABLE MyTable (
  ID INT NOT NULL,
  Name NVARCHAR(50)
);

INSERT INTO MyTable (ID, Name)
VALUES (GetNextID(), 'Record 1');

INSERT INTO MyTable (ID, Name)
VALUES (GetNextID(), 'Record 2');

INSERT INTO MyTable (ID, Name)
VALUES (GetNextID(), 'Record 3');

This code will create a function called GetNextID() that returns the next available ID value for the MyTable table. The function will first select the maximum ID value from the MyTable table, and then add 1 to it. If the MyTable table is empty, then the function will return 1.

The code will then create a table called MyTable with two columns: ID and Name. The ID column is not an identity column, but instead will be populated by the GetNextID() function.