Estatísticas desaparecendo / vazias aleatoriamente ao longo do dia

Eu tenho um banco de dados do SQL Server 2017 (CU9) que exibe alguns problemas relacionados ao desempenho que acredito ter a ver com as estatísticas do índice. Durante a solução de problemas, descobri que as estatísticas não foram atualizadas (o que significa que DBCC SHOW_STATISTICS retornaria todos os valores NULL).

Executei UPDATE STATISTICS na tabela afetada e verifiquei que SHOW_STATISTICS retornou valores reais às 16h de ontem. Esta manhã, às 8:00 da manhã, as estatísticas estavam novamente vazias (retornando valores NULL).

O cliente tem um trabalho de manutenção agendado para ser executado diariamente às 04:00, reindexando para o banco de dados seguido por uma execução de sp_updatestats no banco de dados inteiro. Eu verifiquei que as estatísticas são atualizadas às 04:00 com um rastreamento de criador de perfil.

Não sei por que as estatísticas estariam vazias. É o trabalho de manutenção em execução às 04:00? Existe um bug que não conheço nesta versão do SQL Server?

Agradecemos antecipadamente a sua ajuda.

MAIS INFORMAÇÕES:

• Estatísticas de atualização automática está habilitado.
• A Atualização automática de estatísticas de forma assíncrona está desabilitada.
• A criação automática de estatísticas incrementais está desativada.

Script de reindexação (ofuscado):

USE DBNAME;
DECLARE @CERTENG_Lock INT
DECLARE @WebSite_Control_ProcessRunning_Lock INT
DECLARE @WebSite_Control_Disabled_Lock INT
DECLARE @LogMessage VARCHAR(1024)

SELECT @CERTENG_Lock = Lock FROM application.CERTENG_Lock

SELECT @WebSite_Control_Disabled_Lock = MAX(CAST(Disabled AS INT)), 
       @WebSite_Control_ProcessRunning_Lock = MAX(CAST(ProcessRunning AS INT)) 
  FROM application.WebSite_Control 
 WHERE Webname = 'Reports'

IF(@CERTENG_Lock = 0 AND @WebSite_Control_Disabled_Lock = 0 AND 
@WebSite_Control_ProcessRunning_Lock = 0)
BEGIN
    EXECUTE Dba.ReIndex
END

ELSE
BEGIN
SET @LogMessage = 'The reindex job did not run because the following locks were set: '
IF(@CERTENG_Lock = 1)
BEGIN
    SET @LogMessage = @LogMessage + 'The CERTENG_Lock was set to 1;'
END

IF(@WebSite_Control_Disabled_Lock = 1)
BEGIN
    SET @LogMessage = @LogMessage + 'The WebSite_Control_Disabled_Lock was set to 1;'
END

IF(@WebSite_Control_ProcessRunning_Lock = 1)
BEGIN
    SET @LogMessage = @LogMessage + 'The WebSite_Control_ProcessRunning_Lock was set to 1;'
END

INSERT INTO [Dba].[ReindexLog] ([LogMessage]) VALUES (@LogMessage)

END

DBA.Reindex

USE [Database]
GO
/****** Object:  StoredProcedure [Dba].[ReIndex]    Script Date: 12/20/2018 11:15:33 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

--Create procedure to perform reindexing

ALTER PROCEDURE [Dba].[ReIndex] (
    -- Only rebuild if fragmentation is above ___
    @REBUILD_FRAGMENTATION_THRESHOLD FLOAT = 30,
    -- Or only reorganize if fragmentation is above ___
    @REORG_FRAGMENTATION_THRESHOLD FLOAT = 10
    )
AS
SET NOCOUNT ON;

DECLARE @WorkingId BIGINT, @ReindexId BIGINT, @Sql VARCHAR(2000);
DECLARE @TableId INT, @IndexId INT;
DECLARE @ExecutionTime DATETIME

SET @ExecutionTime = GETDATE()

-------------Identify tables------------------------------------------------------------
TRUNCATE TABLE Dba.ReindexList;

-- List all the tables and their indexes in the database by the number of rows
-- in order to do the largest tables first.
INSERT INTO Dba.ReindexList (SchemaName, TableName, IndexName, TableId, IndexId, IndexType, NumberOfRows)
SELECT s.NAME AS [SchemaName], t.NAME AS [TableName], i.NAME AS [IndexName], i.object_id, i.index_id, i.type_desc, p.row_count
  FROM sys.schemas AS s
 INNER JOIN sys.tables AS t
    ON t.schema_id = s.schema_id
 INNER JOIN sys.indexes AS i
    ON i.object_id = t.object_id
 INNER JOIN sys.dm_db_partition_stats AS p
    ON p.object_id = i.object_id
   AND p.index_id = i.index_id
-- Ignore heaps because they can't be rebuilt or reorganized
 WHERE i.type_desc != 'HEAP'
    -- Skip individual schemas owned by domain accounts
   AND charindex('\', s.NAME) = 0
    -- Skip DBA schema
   AND s.NAME != 'Dba'
 ORDER BY p.row_count DESC, s.NAME, t.NAME, i.index_id;

----------------Check fragmentation---------------------------------------------------
DECLARE
    -- Separate table to keep track of only the indexes that need to be now
    @FragmentationWorkingList TABLE (ReindexId BIGINT NOT NULL PRIMARY KEY CLUSTERED);

INSERT INTO @FragmentationWorkingList (ReindexId)
SELECT r.ReindexId
  FROM Dba.ReindexList AS r
-- Skip fragmentation check for this specific index or table?
  LEFT JOIN Dba.ReindexSetting AS st
    ON st.DatabaseName = db_name()
   AND st.SchemaName = r.SchemaName
   AND st.TableName = r.TableName
   AND st.IndexName IS NULL
  LEFT JOIN Dba.ReindexSetting AS si
    ON si.DatabaseName = db_name()
   AND si.SchemaName = r.SchemaName
   AND si.TableName = r.TableName
   AND si.IndexName = r.IndexName
 WHERE r.IsFragmentationChecked = 'N'
   AND r.IsReindexed = 'N'
    -- Index setting overrides table setting if both are specified
   AND coalesce(si.SkipFragmentationCheck, st.SkipFragmentationCheck, 'N') = 'N'
 ORDER BY r.ReindexId;

SELECT @ReindexId = min(w.ReindexId)
  FROM @FragmentationWorkingList AS w;

WHILE @ReindexId IS NOT NULL
BEGIN
    -- Pull IDs into variables because the physical stats DM function can't
    -- cross-apply values from a JOIN.
    SELECT @TableId = r.TableId, @IndexId = r.IndexId
      FROM Dba.ReindexList AS r
     WHERE r.ReindexId = @ReindexId;

    -- Load the fragmentation for each index individually
    -- with duration-tracking so we can figure out whether or not
    -- this is really worthwhile.
    UPDATE Dba.ReindexList
       SET FragmentationCheckStartTime = getdate()
     WHERE ReindexId = @ReindexId;

    UPDATE r
       SET Fragmentation = p.avg_fragmentation_in_percent
      FROM Dba.ReindexList AS r
    -- Use LIMITED for fastest scan
     INNER JOIN sys.dm_db_index_physical_stats(db_id(), @TableId, @IndexId, NULL, 'LIMITED') AS p
        -- Should only return one row for this index
        ON 1 = 1
     WHERE r.ReindexId = @ReindexId;

    UPDATE Dba.ReindexList
       SET IsFragmentationChecked = 'Y', FragmentationCheckEndTime = getdate()
     WHERE ReindexId = @ReindexId;

    SELECT @ReindexId = min(w.ReindexId)
      FROM @FragmentationWorkingList AS w
     WHERE w.ReindexId > @ReindexId;
END

------------------------------Reindex------------------------------------
DECLARE
    -- Separate table to keep track of only the indexes that need to be now
    @ReindexWorkingList TABLE (
    -- Order differently based on row count and fragmentation
    WorkingId BIGINT NOT NULL identity(1, 1) PRIMARY KEY CLUSTERED, ReindexId BIGINT NOT NULL
    );

INSERT INTO @ReindexWorkingList (ReindexId)
SELECT r.ReindexId
  FROM Dba.ReindexList AS r
-- Skip fragmentation check for this specific index or table?
  LEFT JOIN Dba.ReindexSetting AS st
    ON st.DatabaseName = db_name()
   AND st.SchemaName = r.SchemaName
   AND st.TableName = r.TableName
   AND st.IndexName IS NULL
  LEFT JOIN Dba.ReindexSetting AS si
    ON si.DatabaseName = db_name()
   AND si.SchemaName = r.SchemaName
   AND si.TableName = r.TableName
   AND si.IndexName = r.IndexName
 WHERE r.IsReindexed = 'N'
    -- Index setting overrides table setting if both are specified
   AND coalesce(si.SkipReindex, st.SkipReindex, 'N') = 'N'
    -- Process tables in order of the most fragmented, largest
   AND r.Fragmentation >= @REORG_FRAGMENTATION_THRESHOLD
 ORDER BY r.Fragmentation DESC, r.NumberOfRows DESC, r.ReindexId;

SELECT @WorkingId = min(w.WorkingId)
  FROM @ReindexWorkingList AS w;

WHILE @WorkingId IS NOT NULL
BEGIN
    SELECT @ReindexId = w.ReindexId
      FROM @ReindexWorkingList AS w
     WHERE w.WorkingId = @WorkingId;

    -- Skip index because of low fragmentation?
    IF @REORG_FRAGMENTATION_THRESHOLD > (
            -- Assume that an index is highly fragmented if the exact %
            -- wasn't calculated to save time
            SELECT isnull(r.Fragmentation, 100)
              FROM Dba.ReindexList AS r
             WHERE r.ReindexId = @ReindexId
            )
    BEGIN
        UPDATE Dba.ReindexList
           SET IsReindexed = 'Y', IsSkipped = 'Y', ReindexStartTime = getdate(), ReindexEndTime = getdate()
         WHERE ReindexId = @ReindexId;
    END
            -- Rebuild or reorganize...
    ELSE
    BEGIN
        -- Try/catch inside a loop causes slower performance, but reindexing
        -- should continue on the next index if an error occurs.
        BEGIN TRY
            -- Rebuild or reorganize?
            -- 1) Ignore heaps
            -- 2) Always rebuild a clustered index
            -- 3) Rebuild nonclustered if > __, otherwise reorganize it
            -- According to Kalen Delaney (http://social.msdn.microsoft.com/Forums/en/sqldatabaseengine/thread/dd612296-5b3a-40f1-829f-c654b835efed),
            -- rebuild always updates statistics with FULLSCAN while reorgnize does not.
            SELECT @Sql = 'alter index [' + r.IndexName + '] on [' + r.SchemaName + '].[' + r.TableName + '] ' + 
                   CASE WHEN IndexType = 'HEAP'                               THEN 'rebuild'
                        WHEN IndexType = 'CLUSTERED'                          THEN 'rebuild'
                        WHEN Fragmentation > @REBUILD_FRAGMENTATION_THRESHOLD THEN 'rebuild'
                        ELSE 'reorganize; update statistics [' + r.SchemaName + '].[' + r.TableName + '] [' + r.IndexName + ']'
                    END +
                -- TODO: Handle partitions properly
                ';'
             FROM Dba.ReindexList AS r
            WHERE r.ReindexId = @ReindexId;

            UPDATE Dba.ReindexList
               SET ReindexStartTime = getdate(), Sql = @Sql
             WHERE ReindexId = @ReindexId;

            EXECUTE (@sql);

            UPDATE Dba.ReindexList
               SET ReindexEndTime = getdate(), IsReindexed = 'Y'
             WHERE ReindexId = @ReindexId;
        END TRY

        BEGIN CATCH
            UPDATE Dba.ReindexList
               SET ReindexEndTime = getdate(),
                -- Mark as reindexed to show that an attempt was made...
                   IsReindexed = 'Y', ErrorNumber = error_number(), ErrorMessage = error_message()
             WHERE ReindexId = @ReindexId;
        END CATCH
    END

    SELECT @WorkingId = min(w.WorkingId)
      FROM @ReindexWorkingList AS w
     WHERE w.WorkingId > @WorkingId;
END

INSERT INTO Dba.ReindexHistory (HistoryTime, TableId, IndexId, SchemaName, TableName, IndexName, IsClustered, IsReindexed, NumberOfRows, Fragmentation)
SELECT isnull(@ExecutionTime, getdate()), l.TableId, l.IndexId, l.SchemaName, l.TableName, l.IndexName, 
       CASE l.IndexType WHEN 'CLUSTERED' THEN 'Y'
                        ELSE 'N'
       END AS IsClustered, 
       l.IsReindexed, l.NumberOfRows, l.Fragmentation
  FROM Dba.ReindexList AS l
  LEFT JOIN Dba.ReindexHistory AS h
    ON h.HistoryTime = l.FragmentationCheckStartTime
   AND h.TableId = l.TableId
   AND h.IndexId = l.IndexId
 WHERE h.HistoryTime IS NULL
 ORDER BY l.FragmentationCheckStartTime, l.TableId, l.IndexId;

ATUALIZAÇÃO: desabilitei as Estatísticas de atualização automática do banco de dados e atualizei as estatísticas manualmente ontem. Esta manhã eles ainda estão povoados. Suponho que isso significa que algo de ruim está acontecendo na Atualização automática.

Use o rastreio padrão do sistema para ver qual processo está descartando e recriando estatísticas.

A consulta a seguir mostrará eventos de rastreamento em que um objeto de estatística foi descartado:

SET NOCOUNT ON;

DECLARE @trcfilename nvarchar(260);
DECLARE @trcPath nvarchar(260);

SELECT @trcPath = t.path
FROM sys.traces t
WHERE t.is_default = 1;

SET @trcPath = LEFT(@trcPath, LEN(@trcPath) - (CHARINDEX(N'\', REVERSE(@trcPath))));-- + '\log_*.trc';
print @trcPath
IF OBJECT_ID(N'tempdb..#TraceFiles', N'U') IS NOT NULL
BEGIN
    DROP TABLE #TraceFiles;
END
CREATE TABLE #TraceFiles
(
    TraceFileName nvarchar(260) NOT NULL
    , depth int
    , [file] int
);

INSERT INTO #TraceFiles (TraceFileName, depth, [file])
EXEC sys.xp_dirtree @trcPath, 1, 1; --level 1, show files.

IF OBJECT_ID('tempdb..#trctemp', N'U') IS NOT NULL
BEGIN
    DROP TABLE #trctemp;
END

DECLARE cur CURSOR LOCAL FORWARD_ONLY STATIC READ_ONLY
FOR
SELECT @trcPath + N'\' + TraceFileName 
FROM #TraceFiles tf
WHERE tf.TraceFileName LIKE 'log_%'
    AND tf.depth = 1
    AND tf.[file] = 1
ORDER BY tf.TraceFileName;

OPEN cur;
FETCH NEXT FROM cur INTO @trcFilename
WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT N'Fetching trace events from ' + @trcFilename;
    IF OBJECT_ID(N'tempdb..#trctemp', N'U') IS NULL
    BEGIN
        SELECT *
        INTO #trctemp
        FROM sys.fn_trace_gettable(@trcfilename, default) tt
    END
    ELSE
    BEGIN
        INSERT INTO #trctemp
        SELECT *
        FROM sys.fn_trace_gettable(@trcfilename, default) tt
    END
    FETCH NEXT FROM cur INTO @trcFilename
END
CLOSE cur;
DEALLOCATE cur;


SELECT tt.*
FROM #trctemp tt
WHERE tt.ObjectType = 21587 --Statistics
    AND tt.EventClass = 47 --Object Deleted
ORDER BY tt.EventSequence;