Avaliar e corrigir a integridade do índice columnstore clusterizado em um pool de SQL dedicado

Aplica-se a: Azure Synapse Analytics

Este artigo apresenta uma abordagem ligeiramente diferente para avaliar a integridade do CCI (índice columnstore clusterizado). Siga as etapas nas seções a seguir ou execute as etapas no notebook por meio do Azure Data Studio.

Em geral, dois fatores principais afetam a qualidade de um CCI:

• Grupos de linhas compactos e metadados – a contagem real de grupos de linhas está próxima da contagem ideal para o número de linhas no grupo de linhas.

• Grupos de linhas compactados – Grupos de linhas estão usando compactação columnstore.

Outras condições, como tabelas pequenas, tabelas superpartidas ou tabelas subpartidas, são indiscutivelmente de má qualidade ou saúde. No entanto, essas condições são mais bem classificadas como oportunidades de aprimoramento de design que podem ser avaliadas na Etapa 4.

Etapa 1: analisar um resumo da integridade do CCI

Use a consulta a seguir para obter uma única linha de métricas.

WITH cci_detail AS (
    SELECT t.object_id,
          rg.partition_number,
          COUNT(*) AS total_rowgroup_count,
          SUM(CASE WHEN rg.state = 1 THEN 1 END) AS open_rowgroup_count,
          CEILING((SUM(rg.[total_rows]) - SUM(rg.deleted_rows))/COUNT(DISTINCT rg.distribution_id)/1048576.) * COUNT(DISTINCT rg.distribution_id) AS [ideal_rowgroup_count],
          SUM(rg.size_in_bytes/1024/1024.) AS size_in_mb,
          SUM(CASE WHEN rg.state = 1 THEN rg.size_in_bytes END /1024/1024.) AS open_size_in_mb
   FROM sys.pdw_nodes_column_store_row_groups rg
   JOIN sys.pdw_nodes_tables nt ON rg.object_id = nt.object_id
       AND rg.pdw_node_id = nt.pdw_node_id
       AND rg.distribution_id = nt.distribution_id
   JOIN sys.pdw_table_mappings mp ON nt.name = mp.physical_name
   JOIN sys.tables t ON mp.object_id = t.object_id
   GROUP BY t.object_id,
            rg.partition_number
)
SELECT COUNT(DISTINCT object_id) AS tables_assessed_count,
       COUNT(*) AS partitions_assessed_count,
       SUM(total_rowgroup_count) AS actual_rowgroup_count,
       SUM(ideal_rowgroup_count) AS ideal_rowgroup_count,
       SUM(open_rowgroup_count) AS uncompressed_rowgroup_count,
       CAST(SUM(size_in_mb) AS DECIMAL(19, 4)) AS actual_size_in_mb,
       CAST(SUM(open_size_in_mb) AS DECIMAL(19, 4)) AS uncompressed_size_in_mb,
       CAST(((SUM(total_rowgroup_count) - SUM(ideal_rowgroup_count)) / SUM(total_rowgroup_count)) * 100. AS DECIMAL(9, 4)) AS excess_pct,
       CAST(((SUM(total_rowgroup_count) - SUM(ideal_rowgroup_count)) / SUM(total_rowgroup_count)) * 1. AS DECIMAL(9, 4)) * SUM(size_in_mb) AS excess_size_in_mb
FROM cci_detail

Com o resultado, você pode obter uma visão geral da integridade do CCI para o pool de SQL dedicado. Essas informações não são diretamente acionáveis, mas ajudam você a entender a importância das rotinas de manutenção para alcançar um estado ideal.

Etapa 2: analisar informações detalhadas do CCI

A consulta a seguir fornece um relatório detalhado de quais partições de tabela são candidatos à reconstrução. Os detalhes do CCI são fornecidos em três métricas que ajudam a identificar e priorizar tabelas/partições que se beneficiariam mais da manutenção. Defina os valores de limite apropriados para essas métricas na WHERE cláusula e, em seguida, na ORDER BY cláusula, use as métricas que são de maior interesse para você. As informações detalhadas também podem ser úteis para determinar se o pool de SQL dedicado está sendo afetado por um grande número de tabelas pequenas e fragmentadas, o que pode levar a atrasos na compilação.

WITH cci_info AS(
    SELECT t.object_id AS [object_id],
          MAX(schema_name(t.schema_id)) AS [schema_name],
          MAX(t.name) AS [table_name],
          rg.partition_number AS [partition_number],
          COUNT(DISTINCT rg.distribution_id) AS [distribution_count],
          SUM(rg.size_in_bytes/1024/1024) AS [size_in_mb],
          SUM(rg.[total_rows]) AS [row_count_total],
          COUNT(*) AS [total_rowgroup_count],
          CEILING((SUM(rg.[total_rows]) - SUM(rg.[deleted_rows]))/COUNT(DISTINCT rg.distribution_id)/1048576.) * COUNT(DISTINCT rg.distribution_id) AS [ideal_rowgroup_count],
          SUM(CASE WHEN rg.[State] = 1 THEN 1 ELSE 0 END) AS [OPEN_rowgroup_count],
          SUM(CASE WHEN rg.[State] = 1 THEN rg.[total_rows] ELSE 0 END) AS [OPEN_rowgroup_rows],
          CAST(SUM(CASE WHEN rg.[State] = 1 THEN rg.[size_in_bytes]/1024./1024. ELSE 0 END) AS DECIMAL(19, 4)) AS [OPEN_rowgroup_size_in_mb],
          SUM(CASE WHEN rg.[State] = 2 THEN 1 ELSE 0 END) AS [CLOSED_rowgroup_count],
          SUM(CASE WHEN rg.[State] = 2 THEN rg.[total_rows] ELSE 0 END) AS [CLOSED_rowgroup_rows],
          CAST(SUM(CASE WHEN rg.[State] = 2 THEN rg.[size_in_bytes]/1024./1024. ELSE 0 END) AS DECIMAL(19, 4)) AS [CLOSED_size_in_mb],
          SUM(CASE WHEN rg.[State] = 3 THEN 1 ELSE 0 END) AS [COMPRESSED_rowgroup_count],
          SUM(CASE WHEN rg.[State] = 3 THEN rg.[total_rows] ELSE 0 END) AS [COMPRESSED_rowgroup_rows],
          CAST(SUM(CASE WHEN rg.[State] = 3 THEN rg.[size_in_bytes]/1024./1024. ELSE 0 END) AS DECIMAL(19, 4)) AS [COMPRESSED_size_in_mb],
          SUM(CASE WHEN rg.[State] = 3 THEN rg.[deleted_rows] ELSE 0 END) AS [COMPRESSED_rowgroup_rows_DELETED]
   FROM sys.[pdw_nodes_column_store_row_groups] rg
   JOIN sys.[pdw_nodes_tables] nt ON rg.[object_id] = nt.[object_id]
       AND rg.[pdw_node_id] = nt.[pdw_node_id]
       AND rg.[distribution_id] = nt.[distribution_id]
   JOIN sys.[pdw_table_mappings] mp ON nt.[name] = mp.[physical_name]
   JOIN sys.[tables] t ON mp.[object_id] = t.[object_id]
   GROUP BY t.object_id,
            rg.partition_number
)
, calc_excess AS(
    SELECT *,
        CAST(((total_rowgroup_count - ideal_rowgroup_count) / total_rowgroup_count) * 100. AS DECIMAL(9, 4)) AS [excess_pct],
        CAST(((total_rowgroup_count - ideal_rowgroup_count) / total_rowgroup_count) * 1. AS DECIMAL(9, 4)) * size_in_mb AS [excess_size_in_mb]
   FROM cci_info
)
SELECT calc_excess.* 
    -- , script.*
FROM calc_excess
-- CROSS APPLY dbo.fnMs_GenerateIndexMaintenanceScript(object_id, partition_number) AS script
WHERE -- set your own threshold(s) for the following; 0 is the ideal, but usually not practical
  calc_excess.[excess_size_in_mb] > 300
  OR calc_excess.excess_pct > 0.1
  OR calc_excess.OPEN_rowgroup_size_in_mb > 100
ORDER BY calc_excess.[excess_size_in_mb] DESC;

Etapa 3: o que fazer quando a manutenção não melhora a integridade do CCI

Executar a manutenção em uma tabela/partição pode resultar em um dos seguintes cenários:

• excess_pct ou excess_size_in_mb é maior do que era antes da manutenção.
• A instrução de manutenção falha com memória insuficiente.

Causas típicas

• Recursos insuficientes.
• DWU (nível de serviço insuficiente).
• A tabela é grande e não particionada.

Mitigações recomendadas

• Aumente os recursos para as instruções de manutenção alterando a classe de recurso ou o grupo de carga de trabalho do usuário em execução.
• Aumente temporariamente o nível de DWU para executar a manutenção.
• Implemente uma estratégia de partição para a tabela problemática e execute a manutenção nas partições.

Etapa 4: verifique se há oportunidades de aprimoramento de design

Embora não seja abrangente, a consulta a seguir pode ajudá-lo a identificar possíveis oportunidades comumente encontradas para causar problemas de desempenho ou manutenção em relação às CCIs.

WITH cci_info AS (
    SELECT t.object_id AS [object_id],
          MAX(SCHEMA_NAME(t.schema_id)) AS [schema_name],
          MAX(t.name) AS [table_name],
          rg.partition_number AS [partition_number],
          SUM(rg.[total_rows]) AS [row_count_total],
          CEILING((SUM(rg.[total_rows]) - SUM(rg.[deleted_rows]))/COUNT(DISTINCT rg.distribution_id)/1048576.) * COUNT(DISTINCT rg.distribution_id) AS [ideal_rowgroup_count]
   FROM sys.[pdw_nodes_column_store_row_groups] rg
   JOIN sys.[pdw_nodes_tables] nt ON rg.[object_id] = nt.[object_id]
       AND rg.[pdw_node_id] = nt.[pdw_node_id]
       AND rg.[distribution_id] = nt.[distribution_id]
   JOIN sys.[pdw_table_mappings] mp ON nt.[name] = mp.[physical_name]
   JOIN sys.[tables] t ON mp.[object_id] = t.[object_id]
   GROUP BY t.object_id,
            rg.partition_number
)
SELECT object_id,
       MAX(SCHEMA_NAME),
       MAX(TABLE_NAME),
       COUNT(*) AS number_of_partitions,
       MAX(row_count_total) AS max_partition_row_count,
       MAX(ideal_rowgroup_count) partition_ideal_row_count,
       CASE
           -- non-partitioned tables
           WHEN COUNT(*) = 1 AND MAX(row_count_total) < 15000000 THEN 'Small table'
           WHEN COUNT(*) = 1 AND MAX(ideal_rowgroup_count) > 180 THEN 'Partitioning opportunity'
           -- partitioned tables
           WHEN COUNT(*) > 1 AND MAX(row_count_total) < 15000000 THEN 'Over-partitioned table'
           WHEN COUNT(*) > 1 AND MAX(ideal_rowgroup_count) > 180 THEN 'Under-partitioned table'
       END AS warning_category
FROM cci_info
GROUP BY object_id

Gerar scripts de manutenção de índice

Execute a consulta a seguir para criar dbo.fnMs_GenerateIndexMaintenanceScript a função no pool de SQL dedicado. Essa função gera scripts para otimizar o CCI de três maneiras. Você pode usar essa função para manter índices não apenas CCIs, mas também clusterizados (rowstore).

Parameters

Tabela de saída

CREATE FUNCTION dbo.fnMs_GenerateIndexMaintenanceScript (@object_id INT, @partition_number INT = 1)
RETURNS TABLE
AS
RETURN(
    WITH base_info AS (
        SELECT
            t.object_id
            , SCHEMA_NAME(t.schema_id) AS [schema_name]
            , t.name AS table_name
            , i.index_type
            , i.index_cols
            , i.index_type_desc
            , tdp.distribution_policy_desc
            , c.name hash_distribution_column_name
        FROM sys.tables t
            JOIN (
                SELECT
                    i.object_id
                    , i.index_id
                    , MAX(i.type) AS index_type
                    , MAX(CASE WHEN i.type = 5 AND ic.column_store_order_ordinal != 0 THEN ' ORDER ' ELSE '' END)
                        + '(' + STRING_AGG(
                        CASE
                            WHEN i.type IN (1, 5) 
                                AND (ic.key_ordinal != 0 OR ic.column_store_order_ordinal != 0)
                                THEN c.name + CASE WHEN ic.is_descending_key = 1 THEN ' DESC' ELSE '' END
                        END
                        , ',') WITHIN GROUP(ORDER BY ic.column_store_order_ordinal, ic.key_ordinal) + ')' AS index_cols
                    , MAX(i.type_desc)
                        + CASE
                            WHEN MAX(i.type) IN (1, 5) THEN ' INDEX'
                            ELSE ''
                        END COLLATE SQL_Latin1_General_CP1_CI_AS AS index_type_desc
                FROM sys.indexes i
                    JOIN sys.index_columns ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id
                    JOIN sys.columns c ON ic.object_id = c.object_id AND ic.column_id = c.column_id
                WHERE i.index_id <= 1
                GROUP BY i.object_id, i.index_id
            ) AS i
                ON t.object_id = i.object_id
            JOIN sys.pdw_table_distribution_properties tdp ON t.object_id = tdp.object_id
            LEFT JOIN sys.pdw_column_distribution_properties cdp ON t.object_id = cdp.object_id AND cdp.distribution_ordinal = 1
            LEFT JOIN sys.columns c ON cdp.object_id = c.object_id AND cdp.column_id = c.column_id
        WHERE t.object_id = @object_id
    )
    , param_data_type AS (
        SELECT
            pp.function_id
            , typ.name AS data_type_name
            , CAST(CASE
                WHEN typ.collation_name IS NOT NULL THEN 1
                WHEN typ.name LIKE '%date%' THEN 1
                WHEN typ.name = 'uniqueidentifier' THEN 1
                ELSE 0
            END AS BIT) AS use_quotes_on_values_flag
        FROM sys.partition_parameters pp
            JOIN sys.types typ ON pp.user_type_id = typ.user_type_id
    )
    , boundary AS (
        SELECT
            t.object_id
            , c.name AS partition_column_name
            , pf.boundary_value_on_right
            , prv.boundary_id
            , prv.boundary_id + CASE WHEN pf.boundary_value_on_right = 1 THEN 1 ELSE 0 END AS [partition_number]
            , CASE
                WHEN pdt.use_quotes_on_values_flag = 1 THEN '''' + CAST(
                    CASE pdt.data_type_name
                        WHEN 'date' THEN CONVERT(char(10), prv.value, 120)
                        WHEN 'smalldatetime' THEN CONVERT(VARCHAR, prv.value, 120)
                        WHEN 'datetime' THEN CONVERT(VARCHAR, prv.value, 121)
                        WHEN 'datetime2' THEN CONVERT(VARCHAR, prv.value, 121)
                        ELSE prv.value
                    END    
                    AS VARCHAR(32)) + ''''
                ELSE CAST(prv.value AS VARCHAR(32))
            END AS boundary_value
        FROM sys.tables t
            JOIN sys.indexes i ON t.object_id = i.object_id AND i.index_id <= 1
            JOIN sys.index_columns ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id AND ic.partition_ordinal = 1
            JOIN sys.columns c ON ic.object_id = c.object_id AND ic.column_id = c.column_id
            JOIN sys.partition_schemes ps ON i.data_space_id = ps.data_space_id
            JOIN sys.partition_functions pf ON ps.function_id = pf.function_id
            JOIN param_data_type pdt ON pf.function_id = pdt.function_id
            JOIN sys.partition_range_values prv ON pf.function_id = prv.function_id
        WHERE t.object_id = @object_id
    )
    , partition_clause AS (
        SELECT
            object_id
            , COUNT(*) - 1 -- should always be the 2nd to last partition in stage table
                + CASE WHEN MAX([partition_number]) = @partition_number THEN 1 ELSE 0 END -- except when last partition
                AS [source_partition_number]
            , 'WHERE ' + MAX(partition_column_name)
                + CASE WHEN MAX(CAST(boundary_value_on_right AS TINYINT)) = 1 THEN 
                    ' >= ' + MIN(CASE WHEN [partition_number] = @partition_number THEN boundary_value END)
                    ELSE 
                    ' <= ' + MAX(CASE WHEN [partition_number] = @partition_number THEN boundary_value END)
                END
                + ' AND ' + MAX(partition_column_name)
                + CASE WHEN MAX(CAST(boundary_value_on_right AS TINYINT)) = 1 THEN 
                    ' < ' + MAX(boundary_value)
                    ELSE
                    ' > ' + MIN(boundary_value)
                END AS filter_clause
            , ', PARTITION (' + MAX(partition_column_name) + ' RANGE ' 
                + CASE WHEN MAX(CAST(boundary_value_on_right AS TINYINT)) = 1 THEN 'RIGHT' ELSE 'LEFT' END 
                + ' FOR VALUES(' + STRING_AGG(boundary_value, ',') + '))' AS [partition_clause]
        FROM boundary
        WHERE [partition_number] BETWEEN @partition_number - 1 AND @partition_number + 1
        GROUP BY object_id
    )
    SELECT
        CASE WHEN index_type IN (1, 5) THEN 'ALTER INDEX ALL ON [' + [schema_name] + '].[' + [table_name] + '] REBUILD' 
            + CASE WHEN partition_clause.[object_id] IS NOT NULL THEN ' PARTITION = ' + CAST(@partition_number AS VARCHAR(16)) ELSE '' END + ';' END AS [rebuild_script]
        , CASE WHEN index_type IN (1, 5) THEN 'ALTER INDEX ALL ON [' + [schema_name] + '].[' + [table_name] + '] REORGANIZE' 
            + CASE WHEN partition_clause.[object_id] IS NOT NULL THEN ' PARTITION = ' + CAST(@partition_number AS VARCHAR(16)) ELSE '' END
            + CASE WHEN index_type = 5 THEN ' WITH (COMPRESS_ALL_ROW_GROUPS = ON)' ELSE '' END + ';' END AS [reorganize_script]
        , 'CREATE TABLE [' + schema_name + '].[' + table_name + '_p' + CAST(@partition_number AS VARCHAR(16)) + '_tmp] WITH(' + index_type_desc + ISNULL(index_cols, '')
            + ', DISTRIBUTION = ' + distribution_policy_desc + CASE WHEN distribution_policy_desc = 'HASH' THEN '(' + hash_distribution_column_name + ')' ELSE '' END
            + partition_clause.partition_clause + ') AS SELECT * FROM [' + [schema_name] + '].[' + [table_name] + '] ' + filter_clause + CASE WHEN index_type = 5 AND index_cols IS NOT NULL THEN ' OPTION(MAXDOP 1)' ELSE '' END +  ';'
            + ' ALTER TABLE [' + schema_name + '].[' + table_name + '_p' + CAST(@partition_number AS VARCHAR(16)) + '_tmp] SWITCH PARTITION ' + CAST(source_partition_number AS VARCHAR(16))
            + ' TO [' + [schema_name] + '].[' + [table_name] + '] PARTITION ' + CAST(@partition_number AS VARCHAR(16))
            + ' WITH (TRUNCATE_TARGET = ON);'
            + ' DROP TABLE [' + schema_name + '].[' + table_name + '_p' + CAST(@partition_number AS VARCHAR(16)) + '_tmp];' AS [partition_switch_script]
    FROM base_info
        LEFT JOIN partition_clause
            ON base_info.object_id = partition_clause.object_id
);
GO

Mais informações

Para obter uma compreensão mais detalhada e adquirir ferramentas de avaliação extras para CCI no pool de SQL dedicado, confira:

• caixa de ferramentas Azure Synapse
• Índices em tabelas de pool de SQL dedicadas no Azure Synapse Analytics
• Índices columnstore: visão geral
• Ajuste de desempenho com o índice columnstore clusterizado ordenado
• Índices columnstore – Diretrizes de design