Performance Regression Observed on SQL Server 2025 Running on Windows Server 2025

This was the script executed

SET NOCOUNT ON;
SET XACT_ABORT ON;

DECLARE
    @TotalRows       INT = 200000,
    @BatchSize       INT = 10000,
    @i               INT = 1,
    @StartTime       DATETIME2(7),
    @EndTime         DATETIME2(7),
    @ElapsedMs       BIGINT,
    @CpuStartMs      BIGINT,
    @CpuEndMs        BIGINT,
    @LastReportTime  DATETIME2(7),
    @ReportTime      DATETIME2(7);

------------------------------------------------------------
-- Capture initial CPU time for this SQL session
------------------------------------------------------------
SELECT @CpuStartMs = cpu_time
FROM sys.dm_exec_sessions
WHERE session_id = @@SPID;

SET @StartTime = SYSDATETIME();
SET @LastReportTime = @StartTime;

PRINT '==============================================';
PRINT 'CARDHOLDER INSERT PERFORMANCE TEST';
PRINT '==============================================';
PRINT 'Start Time : ' + CONVERT(VARCHAR(30), @StartTime, 121);
PRINT 'Rows       : ' + CAST(@TotalRows AS VARCHAR(20));
PRINT 'Mode       : ONE INSERT AT A TIME';
PRINT '==============================================';

------------------------------------------------------------
-- Insert 200,000 records - ONE ROW AT A TIME
------------------------------------------------------------
WHILE @i <= @TotalRows
BEGIN

    INSERT INTO[db].[car]
    (
        [last_name],
        [first_name],
        [start_date],
        [end_date],
        [accessibility],
        [timed_reentry_exclusion],
        [guard],
        [active],
        [trace],
        [pin_as_car],
        [supervisor],
        [self_authorise],
        [biometric_encoded],
        [biometric_storage_key],
        [rowguid],
        [rowinstance]
    )
    VALUES
    (
        'TEST_LAST_' + CAST(@i AS VARCHAR(20)),
        'TEST_FIRST_' + CAST(@i AS VARCHAR(20)),
        GETDATE(),
        DATEADD(YEAR, 1, GETDATE()),
        0,
        0,
        0,
        1,
        0,
        0,
        0,
        0,
        0,
        NULL,
        NEWID(),
        NEWID()
    );

    --------------------------------------------------------
    -- Progress every 10,000 rows
    --------------------------------------------------------
    IF @i % @BatchSize = 0
    BEGIN
        SET @ReportTime = SYSDATETIME();

        PRINT
            'Rows: ' +
            CAST(@i AS VARCHAR(20)) +
            ' / ' +
            CAST(@TotalRows AS VARCHAR(20)) +
            ' | Time: ' +
            CAST(DATEDIFF(SECOND, @StartTime, @ReportTime) AS VARCHAR(20)) +
            ' sec';

        SET @LastReportTime = @ReportTime;
    END;

    SET @i = @i + 1;
END;

------------------------------------------------------------
-- End metrics
------------------------------------------------------------
SET @EndTime = SYSDATETIME();

SELECT @CpuEndMs = cpu_time
FROM sys.dm_exec_sessions
WHERE session_id = @@SPID;

SET @ElapsedMs =
    DATEDIFF_BIG(MILLISECOND, @StartTime, @EndTime);

------------------------------------------------------------
-- Final results
------------------------------------------------------------
PRINT '';
PRINT '==============================================';
PRINT 'TEST COMPLETED';
PRINT '==============================================';

SELECT
    @StartTime AS StartTime,
    @EndTime AS EndTime,

    @TotalRows AS RecordsInserted,

    @ElapsedMs AS ElapsedMilliseconds,

    CAST(@ElapsedMs / 1000.0 AS DECIMAL(18,3))
        AS ElapsedSeconds,

    CAST(@ElapsedMs / 60000.0 AS DECIMAL(18,3))
        AS ElapsedMinutes,

    CAST(
        @TotalRows / NULLIF(@ElapsedMs / 1000.0, 0)
        AS DECIMAL(18,2)
    ) AS RecordsPerSecond,

    CAST(
        @ElapsedMs / CAST(@TotalRows AS DECIMAL(18,3))
        AS DECIMAL(18,4)
    ) AS AverageMillisecondsPerRow,

    @CpuStartMs AS CpuStartMilliseconds,

    @CpuEndMs AS CpuEndMilliseconds,

    (@CpuEndMs - @CpuStartMs)
        AS CpuMilliseconds,

    CAST(
        (@CpuEndMs - @CpuStartMs) /
        NULLIF(@ElapsedMs, 0) * 100.0
        AS DECIMAL(18,2)
    ) AS CpuToElapsedPercentage;
GO