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Mise à jour des statistiques à l'aide de Stats_stream ou de FullScan?

la syntaxe pour créer des statistiques est la suivante:

-- Syntax for SQL Server and Azure SQL Database  

UPDATE STATISTICS table_or_indexed_view_name   
    [   
        {   
            { index_or_statistics__name }  
          | ( { index_or_statistics_name } [ ,...n ] )   
                }  
    ]   
    [    WITH   
        [  
            FULLSCAN   
              [ [ , ] PERSIST_SAMPLE_PERCENT = { ON | OFF } ]    
            | SAMPLE number { PERCENT | ROWS }   
              [ [ , ] PERSIST_SAMPLE_PERCENT = { ON | OFF } ]    
            | RESAMPLE   
              [ ON PARTITIONS ( { <partition_number> | <range> } [, ...n] ) ]  
            | <update_stats_stream_option> [ ,...n ]  
        ]   
        [ [ , ] [ ALL | COLUMNS | INDEX ]   
        [ [ , ] NORECOMPUTE ]   
        [ [ , ] INCREMENTAL = { ON | OFF } ] 
        [ [ , ] MAXDOP = max_degree_of_parallelism ] 
    ] ;  

<update_stats_stream_option> ::=  
    [ STATS_STREAM = stats_stream ]  
    [ ROWCOUNT = numeric_constant ]  
    [ PAGECOUNT = numeric_contant ]

et ici Il y a un excellent script par Martin Smith qui script les statistiques avec Stats_stream

lorsque j'exécute ce script dans l'une de mes bases de données de test, je reçois ce qui suit:

DECLARE @Schema             sysname,
        @Table              sysname,
        @StatsName          sysname,
        @IncludeStatsStream BIT,
        @StatsStream        VARCHAR(MAX),
        @TwoPartQuotedName  NVARCHAR(500);

select  @Schema           = 'dbo',
        @Table            = 'tbl_Application_Medical',
        @StatsName        = '_WA_Sys_00000002_7039AB57',
        @IncludeStatsStream = 1;

select @TwoPartQuotedName = QUOTENAME(@Schema) + '.' + QUOTENAME(@Table);


IF @IncludeStatsStream = 1 AND @@MICROSOFTVERSION/ POWER(2,24) > 9
  BEGIN
      DECLARE @StatsResults TABLE
        (
           StatsStream VARBINARY(MAX),
           Rows        BIGINT,
           DataPages   BIGINT
        );

      INSERT INTO @StatsResults
      EXEC sys.sp_executesql 
        N'DBCC SHOW_STATISTICS(@TwoPartQuotedName, @StatsName) WITH STATS_STREAM;',
        N'@TwoPartQuotedName NVARCHAR(500), @StatsName sysname',
        @TwoPartQuotedName = @TwoPartQuotedName,
        @StatsName = @StatsName;

      --Would need some other method on 2005 hence just skipping this
      SELECT @StatsStream = CONVERT(VARCHAR(MAX), StatsStream, 1)
      FROM   @StatsResults;
  END;

WITH stats AS
(
/* 
Support earlier versions without these columns using trick from http://dba.stackexchange.com/a/66755/3690 */
SELECT x.*
FROM (SELECT NULL AS filter_definition, NULL AS is_incremental) AS dummy
CROSS APPLY
(
  SELECT object_id, stats_id, name, no_recompute, filter_definition, is_incremental
  FROM sys.stats
) AS x
)
SELECT '
CREATE STATISTICS ' + QUOTENAME(name) + '   
ON ' + @TwoPartQuotedName + ' (' + SUBSTRING(cols, 2, 10000000) +')
'  + 
ISNULL(' WHERE ' + filter_definition,'') +
ISNULL(STUFF ( 
    ISNULL(',STATS_STREAM = ' + @StatsStream, '') +
    CASE WHEN no_recompute = 1 THEN ',NORECOMPUTE' ELSE '' END + 
    CASE WHEN is_incremental = 1 THEN ',INCREMENTAL=ON' ELSE '' END
 , 1 , 1 ,  ' WITH '  ) , '') AS [processing-instruction(x)]
FROM   stats s
       CROSS APPLY (SELECT ',' + QUOTENAME(c.name)
                    FROM   sys.stats_columns sc
                           JOIN sys.columns c
                             ON c.object_id = sc.object_id
                                AND c.column_id = sc.column_id
                    WHERE  sc.object_id = s.object_id
                           AND sc.stats_id = s.stats_id
                    ORDER  BY sc.stats_column_id
                    FOR XML PATH(''))CA(cols)
WHERE  s.object_id = OBJECT_ID(@TwoPartQuotedName)
       AND s.name = @StatsName
FOR XML PATH('');

select * from @StatsResults

un fichier XML:

<?x CREATE STATISTICS [_WA_Sys_00000002_7039AB57] ON [dbo].[tbl_Application_Medical] ([Smoker]) WITH STATS_STREAM = lot of binary chars that would not fit here?>

enter image description here

lorsque - Mettre à jour les statistiques de toutes les bases de données Toutes les tables d'un serveur Pourrais-je bénéficier de générer le script de statistiques de création avec STATS_SCREAM, au lieu de WITH FULLSCAN?

quelle est la différence entre ces 2?

sql-serverperformanceoptimizationstatisticsautomation
3
Marcello Miorelli

La Autre réponse est correcte, donc au cas où un exemple rend les choses plus claires ...

CREATE TABLE T1
(
C1 VARCHAR(50),
INDEX CIX CLUSTERED(C1)
);

INSERT INTO T1
VALUES ('orange'), ('kiwi'), ('strawberry');


UPDATE STATISTICS [dbo].[T1]([CIX]) 
WITH STATS_STREAM = 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
ROWCOUNT = 3, PAGECOUNT = 1

DBCC SHOW_STATISTICS ( T1 , CIX )  WITH HISTOGRAM;

Les statistiques sont entièrement fictives et ne sont pas liées au contenu de la table. Il utilise simplement l'histogramme codé dans le STATS_STREAM

+--------------+------------+---------+---------------------+----------------+
| RANGE_HI_KEY | RANGE_ROWS | EQ_ROWS | DISTINCT_RANGE_ROWS | AVG_RANGE_ROWS |
+--------------+------------+---------+---------------------+----------------+
| Apple        |          0 |       2 |                   0 |              1 |
| banana       |          0 |       1 |                   0 |              1 |
+--------------+------------+---------+---------------------+----------------+

Mais

UPDATE STATISTICS [dbo].[T1]([CIX]) 
WITH FULLSCAN 

DBCC SHOW_STATISTICS ( T1 , CIX )    WITH HISTOGRAM;

Scanne toutes les rangées de la table de base et crée un nouvel histogramme avec des valeurs correctes

+--------------+------------+---------+---------------------+----------------+
| RANGE_HI_KEY | RANGE_ROWS | EQ_ROWS | DISTINCT_RANGE_ROWS | AVG_RANGE_ROWS |
+--------------+------------+---------+---------------------+----------------+
| kiwi         |          0 |       1 |                   0 |              1 |
| orange       |          0 |       1 |                   0 |              1 |
| strawberry   |          0 |       1 |                   0 |              1 |
+--------------+------------+---------+---------------------+----------------+

Le STATS_STREAM L'option n'est utile que pour le débogage. Il vous permet de copier des histogrammes de la production à une instance de développement sans avoir à copier des données. Cela peut aider à essayer d'évaluer les problèmes de plan de requête.

3
Martin Smith