Valutare e correggere l'integrità dell'indice columnstore cluster in un pool SQL dedicato

Si applica a: Azure Synapse Analytics

Questo articolo introduce un approccio leggermente diverso per la valutazione dell'integrità dell'indice columnstore cluster (CCI). Seguire i passaggi descritti nelle sezioni seguenti o eseguire i passaggi nel notebook tramite Azure Data Studio.

In generale, due fattori principali influiscono sulla qualità di un CCI:

• Compattare rowgroup e metadati : il numero effettivo di rowgroup è vicino al conteggio ideale per il numero di righe nel rowgroup.

• Rowgroup compressi: i rowgroup usano la compressione columnstore.

Altre condizioni, ad esempio tabelle di piccole dimensioni, tabelle sovra partizionate o tabelle sottopartizione, sono probabilmente di scarsa qualità o integrità. Tuttavia, queste condizioni sono classificate meglio come opportunità di miglioramento della progettazione che possono essere valutate nel passaggio 4.

Passaggio 1: Analizzare un riepilogo dell'integrità CCI

Usare la query seguente per ottenere una singola riga di metriche.

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

Dal risultato è possibile ottenere una panoramica dell'integrità CCI per il pool SQL dedicato. Queste informazioni non sono direttamente interattive, ma consentono di comprendere l'importanza delle routine di manutenzione per ottenere uno stato ideale.

Passaggio 2: Analizzare informazioni dettagliate su CCI

La query seguente fornisce un report dettagliato delle partizioni di tabella candidati per la ricompilazione. I dettagli CCI sono disponibili in tre metriche che consentono di identificare e assegnare priorità a tabelle/partizioni che trarrebbero i maggiori vantaggi dalla manutenzione. Impostare i valori soglia appropriati per queste metriche nella WHERE clausola e quindi nella ORDER BY clausola usare le metriche di maggiore interesse. Le informazioni dettagliate possono anche essere utili per determinare se il pool SQL dedicato è interessato da un numero elevato di tabelle frammentate di piccole dimensioni, che possono causare ritardi nella compilazione.

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;

Passaggio 3: Cosa fare quando la manutenzione non migliora l'integrità dell'CCI

L'esecuzione della manutenzione in una tabella/partizione può comportare uno degli scenari seguenti:

• excess_pct o excess_size_in_mb è più grande di prima della manutenzione.
• L'istruzione di manutenzione ha esito negativo con memoria insufficiente.

Cause tipiche

• Risorse insufficienti.
• Livello di servizio (DWU) insufficiente.
• La tabella è di grandi dimensioni e non partizionata.

Mitigazioni consigliate

• Aumentare le risorse per le istruzioni di manutenzione modificando la classe di risorse o il gruppo di carico di lavoro dell'utente in esecuzione.
• Aumentare temporaneamente il livello DWU per eseguire la manutenzione.
• Implementare una strategia di partizionamento per la tabella problematica e quindi eseguire la manutenzione nelle partizioni.

Passaggio 4: Verificare le opportunità di miglioramento della progettazione

Anche se non completa, la query seguente consente di identificare le potenziali opportunità comunemente riscontrate per causare problemi di prestazioni o manutenzione relativi alle 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

Generare script di manutenzione degli indici

Eseguire la query seguente per creare dbo.fnMs_GenerateIndexMaintenanceScript una funzione nel pool SQL dedicato. Questa funzione genera script per ottimizzare l'CCI in tre modi. È possibile usare questa funzione per gestire non solo le CCC, ma anche gli indici cluster (rowstore).

Parametri

Tabella di output

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

Ulteriori informazioni

Per ottenere una comprensione più approfondita e acquisire strumenti di valutazione aggiuntivi per CCI nel pool SQL dedicato, vedere:

• Casella degli strumenti Azure Synapse
• Indici nelle tabelle del pool SQL dedicato in Azure Synapse Analytics
• Indici columnstore: panoramica
• Ottimizzazione delle prestazioni con indice columnstore cluster ordinato
• Indici columnstore - Linee guida per la progettazione