詳解GaussDB(DWS)中3個防過載檢查項

华为云开发者联盟發表於2024-03-18

本文分享自華為雲社群《【防過載檢查項】》，作者： 譡裡個檔。

1. GUC引數檢查

目的：針對不同版本建議設定不同的引數值，當前先檢查出來，後續diagnosis會給出建議值

SELECT
    split_part((substring(version() from '\((.*)\)')), ' ', 2) AS version,
    (EXISTS (SELECT 1 FROM (SELECT count(DISTINCT node_name) AS dn_cnt 
      FROM pgxc_node WHERE node_type = 'D' AND node_host <> 'localhost' GROUP BY node_host) WHERE dn_cnt <> 1)
    ) AS sdn_per_node,
    node_name, name AS guc_name,
    CASE WHEN unit = 'ms' THEN setting::bigint/1000 || ' s'
         WHEN unit = 's' THEN setting || ' s'
         WHEN unit = 'KB' THEN pg_size_pretty(setting*1024)
         WHEN unit = '8KB' THEN pg_size_pretty(setting*1024*8)
         ELSE setting
    END AS setting, unit,
    CASE WHEN name = 'default_distribution_mode' THEN
             CASE WHEN setting <> 'roundrobin' THEN 'roundrobin' END
         WHEN name = 'autovacuum' THEN
             CASE WHEN setting <> 'on' THEN 'on' END
         WHEN name = 'autovacuum_max_workers' THEN
             CASE WHEN setting::int > 6 THEN '6' END
         WHEN name = 'autovacuum_max_workers' THEN
             CASE WHEN setting::int > 3 THEN '3' END
         WHEN name = 'session_timeout' THEN
             CASE WHEN setting::int > 600 OR setting::int = 0 THEN '<= 10min' END
         WHEN name = 'statement_timeout' THEN
             CASE WHEN setting::int > 24* 60 * 1000 OR setting::int = 0 THEN '<= 24h' END
         WHEN name = 'sql_use_spacelimit' THEN
             CASE WHEN setting::int > 300*1024*1024 OR setting IN ('0', '-1') THEN '<= 300GB' END
         WHEN name = 'temp_file_limit' THEN
             CASE WHEN setting::int > 100*1024*1024 OR setting IN ('0', '-1') THEN '<= 100GB' END
         WHEN name = 'udf_memory_limit' THEN
             CASE WHEN setting::int > 1*1024*1024  THEN '<= 1GB' END
         WHEN name = 'query_dop' THEN
             CASE WHEN setting::int = 0 THEN ' -4' END
         WHEN name = 'max_streams_per_query' THEN
             CASE WHEN setting::int = -1 THEN '50' END
         WHEN name = 'max_connections' THEN
             CASE WHEN node_name = 'dn_6001_6002' AND setting::int < 5000 THEN '>=5000' END
         ELSE ''
    END AS diagnosis
FROM pgxc_parallel_query('all', 'SELECT
    pgxc_node_str() AS node_name, name, setting, unit
FROM pg_settings 
WHERE pgxc_node_str() IN (''cn_5001'',''dn_6001_6002'')
AND name in (''max_streams_per_query'',''query_dop''
,''sql_use_spacelimit'',''temp_file_limit'',''default_distribution_mode'',
''autovacuum_mode'',''autovacuum'',''autovacuum_max_workers_hstore'',''autovacuum_max_workers'',
''session_timeout'',''statement_timeout'',''ddl_lock_timeout'',''idle_in_transaction_timeout'',
''max_connections'',''min_pool_size'',''max_pool_size'',
''max_stream_pool'',''max_active_statements'',''max_prepared_transactions'',
''cstore_buffers'',''shared_buffers'', ''max_process_memory'', ''udf_memory_limit'',
''max_process_memory_balanced'', ''bbox_dump_count'', ''enable_bbox_dump'')') 
AS (node_name name, name text, setting text, unit text)
ORDER BY node_name, name;

2. 大表檢查

目的：識別大表，建議客戶整改，避免磁碟過載

8.1.3版本使用如下SQL

SELECT
    CASE WHEN (skewsize > avgsize * 0.10 AND skewsize > 50 * 1024) THEN 'skew table'
        WHEN (reloptions::text LIKE '%orientation=column%' AND reloptions::text LIKE '%compression=no%') THEN 'uncompressed column table'
        WHEN (x.pclocatortype = 'R' AND avgsize > 10 * 1024) THEN 'large replicattion table'
        WHEN (pg_stat_get_dead_tuples(c.oid) >100000 AND pg_stat_get_dead_tuples(c.oid)/(pg_stat_get_dead_tuples(c.oid)+pg_stat_get_live_tuples(c.oid)) > 0.4) THEN 'dirty table'
        ELSE 'normal large table'
    END AS diagnostic,
    t1.schemaname,  -- 表的schema
    t1.tablename,   -- 表名
    a.rolname AS tableowner,
    x.pgroup AS nodegroup,
    CASE x.pclocatortype WHEN 'H' THEN 'Hash' 
        WHEN 'N' THEN 'Round Robin' 
        WHEN 'R' THEN 'Replicate' 
    END AS locatortype,
    CASE WHEN c.parttype = 'p' THEN true ELSE false END AS ispartitioned,
    CASE WHEN reloptions::text LIKE '%orientation=column%' THEN 'column'
         WHEN reloptions::text LIKE '%orientation=row%' THEN 'row'
    END AS orientation,
    t1.dnnum,                         -- 表的node group的DN數
    t1.totalsize AS "totalsize(MB)",  -- 表的size ，單位MB
    t1.avgsize AS "avgsize(MB)",      -- 平均每個DN上資料量，單位MB
    t1.skewsize AS "skewsize(MB)",    -- 不同DN上資料size的最大差值，單位MB
    t1.skewdn,                        -- 資料量最大的DN
    t1.maxratio,                      -- 資料量最大DN的size/平均size
    t1.minratio,                      -- 資料量最小DN的size/平均size
    t1.skewratio                      -- 不同DN上資料size的最大差值/平均size
FROM ( -- 預處理，識別傾斜表
    SELECT
        schemaname,
        tablename,
        skewdn,
        dnnum,
        totalsize,
        avgsize,
        skewsize,
        (maxsize/avgsize)::numeric(20,2) AS maxratio,
        (minsize/avgsize)::numeric(20,2) AS minratio,
        (skewsize/avgsize)::numeric(20,2) AS skewratio
    FROM (
        SELECT
            schemaname,tablename,skewdn,count(1) AS dnnum,sum(dnsize) AS totalsize,
            avg(dnsize) AS avgsize,max(dnsize) AS maxsize,min(dnsize) AS minsize, (max(dnsize) - min(dnsize)) AS skewsize
        FROM ( --對每個表的資料按照DN資料量大小排序，以及獲取傾斜的dn
            SELECT     
                schemaname,
                tablename,
                nodename,
                (dnsize/1024/1024)::bigint AS dnsize, -- 單位換算為MB
                first_value(nodename) over (PARTITION BY schemaname, tablename ORDER BY dnsize DESC, nodename) AS skewdn  -- --資料量最大的DN
            FROM ( -- 獲取大於10GB的表
                SELECT 
                    schemaname, tablename,(rd).nodename, ((rd).dnsize + 1) AS dnsize
                FROM (
                    SELECT
                        schemaname, tablename, gs_table_distribution(schemaname, tablename) AS rd
                    FROM gs_table_distribution()
                    WHERE schemaname NOT IN ('pg_catalog', 'dbms_om', 'cstore')
                    AND relkind = 'r'
                    GROUP BY schemaname, tablename
                    HAVING sum(dnsize) > 50.0 * 1024 * 1024 * 1024 -- 總大小大於100GB
                )
            )
        )
        GROUP BY schemaname,tablename, skewdn
    )
) t1
INNER JOIN pg_class c ON c.relname = t1.tablename
LEFT JOIN pg_namespace n ON n.nspname = t1.schemaname
LEFT JOIN pg_authid a ON a.oid = c.relowner
LEFT JOIN pgxc_class x ON x.pcrelid = c.oid
WHERE c.reloptions::text NOT LIKE '%internal_mask%'
ORDER BY totalsize DESC, diagnostic, skewsize DESC
;

8.2.1和8.2.0版本使用如下

-- 大表診斷
SELECT
    CASE WHEN (skewsize > avgsize * 0.10 AND skewsize > 50 * 1024) THEN 'skew table'
        WHEN (reloptions::text LIKE '%orientation=column%' AND reloptions::text LIKE '%compression=no%') THEN 'uncompressed column table'
        WHEN (x.pclocatortype = 'R' AND avgsize > 10 * 1024) THEN 'large replicattion table'
        WHEN (pg_stat_get_dead_tuples(c.oid) >100000 AND pg_stat_get_dead_tuples(c.oid)/(pg_stat_get_dead_tuples(c.oid)+pg_stat_get_live_tuples(c.oid)) > 0.4) THEN 'dirty table'
        WHEN (reloptions::text LIKE '%orientation=column%') THEN
            CASE WHEN (SELECT total_cu_count > 0 AND (zero_size_cu_count + small_cu_count)/total_cu_count > 0.5 FROM get_col_cu_info(t1.schemaname, t1.tablename)) THEN 'small cu table'
                ELSE 'normal large table'
            END
        ELSE 'normal large table'
    END AS diagnostic,
    t1.schemaname,  -- 表的schema
    t1.tablename,   -- 表名
    a.rolname AS tableowner,
    x.pgroup AS nodegroup,
    CASE x.pclocatortype WHEN 'H' THEN 'Hash' 
        WHEN 'N' THEN 'Round Robin' 
        WHEN 'R' THEN 'Replicate' 
    END AS locatortype,
    CASE WHEN c.parttype = 'p' THEN true ELSE false END AS ispartitioned,
    CASE WHEN reloptions::text LIKE '%orientation=column%' THEN 'column'
         WHEN reloptions::text LIKE '%orientation=row%' THEN 'row'
    END AS orientation,
    t1.dnnum,                         -- 表的node group的DN數
    t1.totalsize AS "totalsize(MB)",  -- 表的size ，單位MB
    t1.avgsize AS "avgsize(MB)",      -- 平均每個DN上資料量，單位MB
    t1.skewsize AS "skewsize(MB)",    -- 不同DN上資料size的最大差值，單位MB
    t1.skewdn,                        -- 資料量最大的DN
    t1.maxratio,                      -- 資料量最大DN的size/平均size
    t1.minratio,                      -- 資料量最小DN的size/平均size
    t1.skewratio                      -- 不同DN上資料size的最大差值/平均size
FROM ( -- 預處理，識別傾斜表
    SELECT
        schemaname,
        tablename,
        skewdn,
        dnnum,
        totalsize,
        avgsize,
        skewsize,
        (maxsize/avgsize)::numeric(20,2) AS maxratio,
        (minsize/avgsize)::numeric(20,2) AS minratio,
        (skewsize/avgsize)::numeric(20,2) AS skewratio
    FROM (
        SELECT
            schemaname,
            tablename,
            skewdn,
            count(1) AS dnnum,
            sum(dnsize) AS totalsize,
            avg(dnsize) AS avgsize,
            max(dnsize) AS maxsize,
            min(dnsize) AS minsize,
            (max(dnsize) - min(dnsize)) AS skewsize
        FROM ( --對每個表的資料按照DN資料量大小排序，以及獲取傾斜的dn
            SELECT     
                schemaname,
                tablename,
                nodename,
                (dnsize/1024/1024)::bigint AS dnsize, -- 單位換算為MB
                first_value(nodename) over (PARTITION BY schemaname, tablename ORDER BY dnsize DESC, nodename) AS skewdn  -- --資料量最大的DN
            FROM ( -- 獲取大於10GB的表
                SELECT 
                    schemaname, tablename,(rd).nodename, ((rd).dnsize + 1) AS dnsize
                FROM (
                    SELECT
                        schemaname, tablename, gs_table_distribution(schemaname, tablename) AS rd
                    FROM gs_table_distribution()
                    WHERE schemaname NOT IN ('pg_catalog', 'dbms_om', 'cstore')
                    AND relkind = 'r'
                    GROUP BY schemaname, tablename
                    HAVING sum(dnsize) > 50* 1024 * 1024 * 1024.0 -- 總大小大於100GB
                )
            )
        )
        GROUP BY schemaname,tablename, skewdn
    )
) t1
INNER JOIN pg_class c ON c.relname = t1.tablename
LEFT JOIN pg_namespace n ON n.nspname = t1.schemaname
LEFT JOIN pg_authid a ON a.oid = c.relowner
LEFT JOIN pgxc_class x ON x.pcrelid = c.oid
WHERE c.reloptions::text NOT LIKE '%internal_mask%'
ORDER BY totalsize DESC, diagnostic, skewsize DESC
;

8.3.0版本使用

-- 大表診斷
SELECT
    CASE WHEN (skewsize > avgsize * 0.10 AND skewsize > 50 * 1024) THEN 'skew table'
        WHEN (reloptions::text LIKE '%orientation=column%' AND reloptions::text LIKE '%compression=no%') THEN 'uncompressed column table'
        WHEN (x.pclocatortype = 'R' AND avgsize > 10 * 1024) THEN 'large replicattion table'
        WHEN (pg_stat_get_dead_tuples(c.oid) >100000 AND pg_stat_get_dead_tuples(c.oid)/(pg_stat_get_dead_tuples(c.oid)+pg_stat_get_live_tuples(c.oid)) > 0.4) THEN 'dirty table'
        WHEN (reloptions::text LIKE '%orientation=column%') THEN
            CASE WHEN (SELECT total_cu_count > 0 AND (zero_cu_count + small_cu_count)/total_cu_count > 0.5 FROM pgxc_get_small_cu_info(c.oid)) THEN 'small cu table'
                ELSE 'normal large table'
            END
        ELSE 'normal large table'
    END AS diagnostic,
    t1.schemaname,  -- 表的schema
    t1.tablename,   -- 表名
    a.rolname AS tableowner,
    x.pgroup AS nodegroup,
    CASE x.pclocatortype WHEN 'H' THEN 'Hash' 
        WHEN 'N' THEN 'Round Robin' 
        WHEN 'R' THEN 'Replicate' 
    END AS locatortype,
    CASE WHEN c.parttype = 'p' THEN true ELSE false END AS ispartitioned,
    CASE WHEN reloptions::text LIKE '%orientation=column%' THEN 'column'
         WHEN reloptions::text LIKE '%orientation=row%' THEN 'row'
    END AS orientation,
    t1.dnnum,                         -- 表的node group的DN數
    t1.totalsize AS "totalsize(MB)",  -- 表的size ，單位MB
    t1.avgsize AS "avgsize(MB)",      -- 平均每個DN上資料量，單位MB
    t1.skewsize AS "skewsize(MB)",    -- 不同DN上資料size的最大差值，單位MB
    t1.skewdn,                        -- 資料量最大的DN
    t1.maxratio,                      -- 資料量最大DN的size/平均size
    t1.minratio,                      -- 資料量最小DN的size/平均size
    t1.skewratio                      -- 不同DN上資料size的最大差值/平均size
FROM ( -- 預處理，識別傾斜表
    SELECT
        schemaname,
        tablename,
        skewdn,
        dnnum,
        totalsize,
        avgsize,
        skewsize,
        (maxsize/avgsize)::numeric(20,2) AS maxratio,
        (minsize/avgsize)::numeric(20,2) AS minratio,
        (skewsize/avgsize)::numeric(20,2) AS skewratio
    FROM (
        SELECT
            schemaname,
            tablename,
            skewdn,
            count(1) AS dnnum,
            sum(dnsize) AS totalsize,
            avg(dnsize) AS avgsize,
            max(dnsize) AS maxsize,
            min(dnsize) AS minsize,
            (max(dnsize) - min(dnsize)) AS skewsize
        FROM ( --對每個表的資料按照DN資料量大小排序，以及獲取傾斜的dn
            SELECT     
                schemaname,
                tablename,
                nodename,
                (dnsize/1024/1024)::bigint AS dnsize, -- 單位換算為MB
                first_value(nodename) over (PARTITION BY schemaname, tablename ORDER BY dnsize DESC, nodename) AS skewdn  -- --資料量最大的DN
            FROM ( -- 獲取大於10GB的表
                SELECT 
                    schemaname, tablename,(rd).nodename, ((rd).dnsize + 1) AS dnsize
                FROM (
                    SELECT
                        schemaname, tablename, gs_table_distribution(schemaname, tablename) AS rd
                    FROM gs_table_distribution()
                    WHERE schemaname NOT IN ('pg_catalog', 'dbms_om', 'cstore')
                    AND relkind = 'r'
                    GROUP BY schemaname, tablename
                    HAVING sum(dnsize) > 50.0 * 1024 * 1024 * 1024 -- 總大小大於100GB
                )
            )
        )
        GROUP BY schemaname,tablename, skewdn
    )
) t1
INNER JOIN pg_class c ON c.relname = t1.tablename
LEFT JOIN pg_namespace n ON n.nspname = t1.schemaname
LEFT JOIN pg_authid a ON a.oid = c.relowner
LEFT JOIN pgxc_class x ON x.pcrelid = c.oid
WHERE c.reloptions::text NOT LIKE '%internal_mask%'
ORDER BY totalsize DESC, diagnostic, skewsize DESC
;

針對不同的診斷結果使用如下診斷措施

類別

建議手段

skew table

根據業務選擇關聯常用，並且資料不傾斜的列作為修改分佈列，如果找不到合適的分佈列，可以把表修改為RoundRobin分佈

ALTER TABLE ctmes_tgmesmbi.mbi_hlottsthisDISTRIBUTE BY ROUNDROBIN;複製
  • 注意：修改分佈列的過程中此表存在雙份資料，因此要預留足夠的磁碟空間，防止導致磁碟空間過載。
  • ALTER TABLE修改分佈列對錶持8級鎖，阻塞此表的SELECT、UPDATE、DELETE、INSERT等操作

uncompressed column table

列存表的壓縮效果非常好，一般推薦使用壓縮，至少使用low級別壓縮

ALTER TABLE customer_address SET(compression=low);
VACUUM FULL customer_address;複製
  • 注意，VACUUM FULL的過程中此表存在雙份資料，因此要預留足夠的磁碟空間，防止VACUUM FULL過程中導致磁碟空間過載。
  • VACUUM FULL對錶持8級鎖，阻塞此表的SELECT、UPDATE、DELETE、INSERT等操作

dirty table

說明表檢測碎片率比較高，需要透過VACUUM整理表

VACUUM FULL customer_address;複製
  • VACUUM FULL的過程中此表存在雙份資料，因此要預留足夠的磁碟空間，防止VACUUM FULL過程中導致磁碟空間過載。
  • VACUUM FULL對錶持8級鎖，阻塞此表的SELECT、UPDATE、DELETE、INSERT等操作

small cu table

說明表小CU比較多，需要透過VACUUM整理表

VACUUM FULL customer_address;複製
  • VACUUM FULL的過程中此表存在雙份資料，因此要預留足夠的磁碟空間，防止VACUUM FULL過程中導致磁碟空間過載。
  • VACUUM FULL對錶持8級鎖，阻塞此表的SELECT、UPDATE、DELETE、INSERT等操作

large replicattion table

複製表在每個DN上都有一份全量資料，當表磁碟空間佔用過大時，需要把表修改為HASH表。一般複製表都是維表，存在主鍵，直接把分佈列修改為主鍵

ALTER TABLE ctmes_tgmesmbi.mbi_hlottsthisDISTRIBUTE BY HASH(id);複製

normal large table

3. 冗餘索引診斷

目的：識別冗餘索引，建議客戶刪除。可以降低磁碟空間，並降低大規模資料匯入的時候的xlog規模

-- optimizable policy為duplicate的檢查項
--        表明兩個索引欄位和欄位順序完全一致
--         建議直接刪除optimizable index指定的索引；
-- optimizable policy為redundancy檢查項表明
--         optimizable index指定的索引的索引列剛好是base index的索引列的前面欄位
--         建議直接刪除optimizable index指定的索引；
-- optimizable policy為optimizable檢查項
--         表明optimizable index和base index這兩個索引的索引列完全重複，但是索引列的順序不一致
--         這種場景需要人工介入分析是否可以最佳化
WITH info AS(
    SELECT 
        quote_ident(n.nspname) || '.' || quote_ident(c.relname) AS tablename,
        pgroup AS nodegroup,
        x.indrelid AS indrelid,
        x.indexrelid AS indexrelid,
        indisunique,
        indisprimary,
        indnatts,
        indkey,
        indexprs
    FROM pg_index x
    INNER JOIN pg_class c ON c.oid = x.indrelid
    INNER JOIN pg_class i ON i.oid = x.indexrelid
    LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
    INNER JOIN pgxc_class xc ON xc.pcrelid = c.oid
    WHERE c.relkind = 'r' AND c.oid >= 16384 AND (c.reloptions IS NULL OR c.reloptions::text NOT LIKE '%internal_mask%')
    AND i.relkind = 'i' AND i.oid >= 16384
    AND x.indpred IS NULL
),

base AS(
    SELECT
        tablename,
        nodegroup,
        i.indrelid,
        i.indexrelid baseidx,
        i.indisunique AS base_unique,
        i.indisprimary AS base_primary,
        x.indexrelid AS optidx,
        x.indisunique AS opt_unique,
        x.indisprimary AS opt_primary,
        CASE WHEN opt_primary > base_primary OR opt_unique > base_unique THEN true ELSE false END AS swap,
        CASE WHEN i.indkey = x.indkey AND coalesce(pg_get_expr(i.indexprs, i.indrelid), 'NULL') = coalesce(pg_get_expr(x.indexprs, x.indrelid), 'NULL') THEN 'duplicate'::text
            WHEN x.indexprs IS NOT NULL OR i.indexprs IS NOT NULL THEN NULL::text
            WHEN strpos(i.indkey::text, x.indkey::text||' ') = 1 OR strpos(x.indkey::text, i.indkey::text||' ') = 1 THEN 'redundancy'::text
            WHEN i.indkey @> x.indkey AND x.indkey @> i.indkey THEN 'optimizable'::text
            ELSE NULL
        END AS optpolicy
    FROM info i
    INNER JOIN pg_index x ON (i.indrelid = x.indrelid AND i.indexrelid > x.indexrelid)
    WHERE x.indpred IS NULL AND optpolicy IS NOT NULL
),

tmp AS(
    SELECT
        tablename,
        indrelid,
        nodegroup,
        CASE WHEN swap THEN optidx       ELSE baseidx      END AS base_idx,
        CASE WHEN swap THEN opt_primary  ELSE base_primary END AS base_primary,
        CASE WHEN swap THEN opt_unique   ELSE base_unique  END AS base_unique,
        CASE WHEN swap THEN baseidx      ELSE optidx       END AS opt_idx,
        CASE WHEN swap THEN base_primary ELSE opt_primary  END AS opt_primary,
        CASE WHEN swap THEN base_unique  ELSE opt_unique   END AS opt_unique,
        optpolicy
    FROM base
)

SELECT
    tablename,
    nodegroup,
    base_idx::regclass::text AS base_index,
    base_primary,
    base_unique,
    substring(pg_get_indexdef(base_idx) from 'USING .+\)') AS base_idxdef,
    opt_idx::regclass::text AS opt_index,
    opt_primary,
    opt_unique,
    substring(pg_get_indexdef(opt_idx) from 'USING .+\)') AS opt_idxdef,
    optpolicy,
    pg_get_tabledef(indrelid)
FROM tmp
ORDER BY 1, 2, 3
;

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