【数仓运维实践】关于GaussDB(DWS)单SQL磁盘空间管控

摘要：本文主要讲解数仓运维中遇到单SQL磁盘空间管控问题的解析和方案。

本文分享自华为云社区《GaussDB(DWS)运维 -- 单SQL磁盘空间管控》，作者：譡里个檔。

【问题描述】

执行部分SQL语句时出现如下报错信息(具体数值可能因为配置有差异)，本文针对根因和场景触发场景，确定触发此类问题的根因

The space used on DN (209715224 kB) has exceeded the sql use space limit (209715200 kB)

【问题根因】

该报错表示用户执行的sql在单DN上所用空间超过了参数sql_use_spacelimit的限制。sql_use_spacelimit限制单个SQL在单个DN上，触发落盘操作时，落盘文件的空间大小，管控的空间包括普通表、临时表以及中间结果集落盘占用的空间

可以使用如下SQL查看所有实例上的配置参数sql_use_spacelimit的值

SELECT * FROM pgxc_settings WHERE name = 'sql_use_spacelimit';

【解决方案】

当前现网最常见的此类错误一般都是INERT语句触发的，我们以常见如下语句为例，说明这类问题的解决方案

INSERT INTO dwljaa.bif_col_edw_dut_257_t

(attribute1, attribute2, attribute3, attribute4, attribute5, column_name1, column_name2,

column_name3, column_name4, column_name5, tag_code, tag_id, table_name, period, tbl_code,

tag_grp_code, target_key_val, cycle_id, creation_date, target_key_num, priority)

SELECT

 'SCN_SVC_3003', NULL, NULL, NULL, NULL, 'BIZ_SCR_CODE', NULL, NULL, NULL, NULL,

 'SCN_SVC_3003-02', 3026937, 'dwr_fin_hwip_man_je_f_tmp0', '202208', 'PL_E17360237',

 'SUB_PL_PUB_SCN', A.record_seq_num, 20230321000000, SYSDATE, A.record_seq_num, 53333

FROM (SELECT /*+PARALLEL(8) NO_EXPAND*/ T.record_seq_num

 FROM dwljaa.dwr_fin_hwip_man_je_f_tmp0 T

 INNER JOIN dwrdim.dwr_dim_department_d PL_E100134 ON T.COA_DEPT_KEY = PL_E100134.DEPT_KEY

 INNER JOIN dwrdim.dwr_dim_grp_acct_code_d PL_E100119 ON T.GROUP_ACCOUNT_CODE = PL_E100119.GROUP_ACCOUNT_CODE

 INNER JOIN dwrdim.dwr_dim_journal_category_d PL_E100147 ON T.JE_CATEGORY_ID = PL_E100147.JE_CATEGORY_ID

 INNER JOIN dwrdim.dwr_dim_product_d PL_E100121 ON T.MAJOR_PROD_KEY = PL_E100121.PROD_KEY

 INNER JOIN dwrdim.dwr_dim_product_d PL_E100122 ON T.MINOR_PROD_KEY = PL_E100122.PROD_KEY

 INNER JOIN dwrdim.dwr_dim_project_d PL_E100155 ON T.PROJ_KEY = PL_E100155.PROJ_KEY

 WHERE 1 = 1 AND ((((((((((PL_E100119.LVL1_ACCOUNT_CODE IN('501', '503', '506', '512')) OR(PL_E100119.GROUP_ACCOUNT_CODE = '5980406')) AND((PL_E100121.PROD_CLASS_FLAG = '0') OR(PL_E100122.PROD_CLASS_FLAG = '0'))) OR((PL_E100119.LVL1_ACCOUNT_CODE IN('504', 'SVC')) OR(PL_E100119.LVL2_ACCOUNT_CODE IN('55107', '57702', '57703', '58303')) OR(PL_E100119.GROUP_ACCOUNT_CODE IN('5980407', '5825107', '5827702', '5827703', 'C501'))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E01', 'E03', 'E05', 'E06', 'E08', 'E09', 'E10', 'E11', 'E02', 'E04', 'E07', 'E12')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE = 'Z4') AND((PL_E100155.PROJ_TYPE_CODE <> '02') OR(PL_E100155.PROJ_NUM IN('9000000')))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E02', 'E04', 'E07', 'E12', 'E05', 'E09', 'E10')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE IN('Z1', 'Z2', 'Z3')) AND(PL_E100155.PROJ_TYPE_CODE = '01'))) AND((PL_E100119.GROUP_ACCOUNT_CODE <> 'EXP5555')))) AND(PL_E100119.LVL2_ACCOUNT_CODE <> '58303') AND(PL_E100155.PROJ_TYPE_CODE = '01'))) AND((PL_E100119.LVL1_ACCOUNT_CODE = '504') AND(PL_E100147.CN_NAME IN('JV-PFC cooper cost', 'JV-ADJ PA Cooper/Constr', 'JV-Agent REV&COST Adj', 'JV-Agent totalvalue Adj')))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE = 'E05') AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE IN('Z1', 'Z2', 'Z3')) AND(PL_E100155.PROJ_TYPE_CODE = '01') AND(PL_E100147.CN_NAME <> 'JV-ADJ 557 WITH B CODE') AND((((((((PL_E100119.LVL1_ACCOUNT_CODE IN('501', '503', '506', '512')) OR(PL_E100119.GROUP_ACCOUNT_CODE = '5980406')) AND((PL_E100121.PROD_CLASS_FLAG = '0') OR(PL_E100122.PROD_CLASS_FLAG = '0'))) OR((PL_E100119.LVL1_ACCOUNT_CODE IN('504', 'SVC')) OR(PL_E100119.LVL2_ACCOUNT_CODE IN('55107', '57702', '57703', '58303')) OR(PL_E100119.GROUP_ACCOUNT_CODE IN('5980407', '5825107', '5827702', '5827703', 'C501'))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E01', 'E03', 'E05', 'E06', 'E08', 'E09', 'E10', 'E11', 'E02', 'E04', 'E07', 'E12')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE = 'Z4') AND((PL_E100155.PROJ_TYPE_CODE <> '02') OR(PL_E100155.PROJ_NUM IN('9000000')))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E02', 'E04', 'E07', 'E12', 'E05', 'E09', 'E10')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE IN('Z1', 'Z2', 'Z3')) AND(PL_E100155.PROJ_TYPE_CODE = '01'))) AND((PL_E100119.GROUP_ACCOUNT_CODE <> 'EXP5555')))) AND(PL_E100119.LVL2_ACCOUNT_CODE <> '58303') AND(PL_E100155.PROJ_TYPE_CODE = '01')))))

 AND T.PERIOD_ID >= 202208

 AND T.PERIOD_ID <= 202208

) A

场景1

1）往目标表INSERT的数据量过大，导致INSERT的数据量在单DN上使用的存储空间超过sql_use_spacelimit阈值

这种场景一般是配置参数sql_use_spacelimit设置不合理，建议直接调大配置参数sql_use_spacelimit的值

2）INSERT的数据存在倾斜，导致某个DN上数据写入量特别大，在这个DN上触发了sql_use_spacelimit阈值

这类问题的解决一般分为以下几个步骤

a）使用如下SQL查找目标表分布列

SELECT pg_get_tabledef('dwljaa.bif_col_edw_dut_257_t'::regclass);

获取的表定义如下

SET search_path = dwljaa;

CREATE TABLE bif_col_edw_dut_257_t (

tag_grp_code character varying(100),

tag_code character varying(100),

tag_id numeric,

period character varying(20),

tbl_code character varying(100) NOT NULL,

table_name character varying(50),

target_key_val character varying(100),

target_key_num numeric,

cycle_id numeric,

creation_date timestamp(0) without time zone,

attribute1 character varying(100),

attribute2 character varying(100),

attribute3 character varying(100),

attribute4 character varying(100),

attribute5 character varying(100),

priority numeric,

column_name1 character varying(100),

column_name2 character varying(100),

column_name3 character varying(100),

column_name4 character varying(100),

column_name5 character varying(100),

carrying_dimension1 character varying(100),

carrying_dimension2 character varying(100),

carrying_dimension3 character varying(100)

)

WITH (orientation=column, compression=low, colversion=2.0, enable_delta=false)

DISTRIBUTE BY HASH(target_key_num)

TO GROUP group_version1;

b）根据表定义和INSERT语句，确认分布列在查询语句中的输出列位置

根据表定义(分布列为target_key_num)以及原始的INSERT语句描述，查询语句输出的导数第二列( A.record_seq_num)对应目标表的分布列target_key_num

c）构建如下查询语句，判断查询语句输出数据在字段A.record_seq_num是否存在严重

如果输出的第一条记录的cnt值非常大(比如上百万甚至更多)，导致此值对应记录的存储空间可能触发sql_use_spacelimit阈值，那么就可以明确是数据倾斜导致的。这种场景一般需要先排查数据倾斜产生的原因是否合理，如果数据缺失存在倾斜，那么建议修改表的分布列，具体修改方案参见《GaussDB(DWS)性能调优系列实战篇三：十八般武艺之好味道表定义》

WITH t AS(-- 把原始语句中的查询部分封装为CTE，查询语句实处列只包含分布列

 SELECT

 A.record_seq_num

 FROM (SELECT /*+PARALLEL(8) NO_EXPAND*/ T.record_seq_num

 FROM dwljaa.dwr_fin_hwip_man_je_f_tmp0 T

 INNER JOIN dwrdim.dwr_dim_department_d PL_E100134 ON T.COA_DEPT_KEY = PL_E100134.DEPT_KEY

 INNER JOIN dwrdim.dwr_dim_grp_acct_code_d PL_E100119 ON T.GROUP_ACCOUNT_CODE = PL_E100119.GROUP_ACCOUNT_CODE

 INNER JOIN dwrdim.dwr_dim_journal_category_d PL_E100147 ON T.JE_CATEGORY_ID = PL_E100147.JE_CATEGORY_ID

 INNER JOIN dwrdim.dwr_dim_product_d PL_E100121 ON T.MAJOR_PROD_KEY = PL_E100121.PROD_KEY

 INNER JOIN dwrdim.dwr_dim_product_d PL_E100122 ON T.MINOR_PROD_KEY = PL_E100122.PROD_KEY

 INNER JOIN dwrdim.dwr_dim_project_d PL_E100155 ON T.PROJ_KEY = PL_E100155.PROJ_KEY

 WHERE 1 = 1 AND ((((((((((PL_E100119.LVL1_ACCOUNT_CODE IN('501', '503', '506', '512')) OR(PL_E100119.GROUP_ACCOUNT_CODE = '5980406')) AND((PL_E100121.PROD_CLASS_FLAG = '0') OR(PL_E100122.PROD_CLASS_FLAG = '0'))) OR((PL_E100119.LVL1_ACCOUNT_CODE IN('504', 'SVC')) OR(PL_E100119.LVL2_ACCOUNT_CODE IN('55107', '57702', '57703', '58303')) OR(PL_E100119.GROUP_ACCOUNT_CODE IN('5980407', '5825107', '5827702', '5827703', 'C501'))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E01', 'E03', 'E05', 'E06', 'E08', 'E09', 'E10', 'E11', 'E02', 'E04', 'E07', 'E12')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE = 'Z4') AND((PL_E100155.PROJ_TYPE_CODE <> '02') OR(PL_E100155.PROJ_NUM IN('9000000')))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E02', 'E04', 'E07', 'E12', 'E05', 'E09', 'E10')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE IN('Z1', 'Z2', 'Z3')) AND(PL_E100155.PROJ_TYPE_CODE = '01'))) AND((PL_E100119.GROUP_ACCOUNT_CODE <> 'EXP5555')))) AND(PL_E100119.LVL2_ACCOUNT_CODE <> '58303') AND(PL_E100155.PROJ_TYPE_CODE = '01'))) AND((PL_E100119.LVL1_ACCOUNT_CODE = '504') AND(PL_E100147.CN_NAME IN('JV-PFC cooper cost', 'JV-ADJ PA Cooper/Constr', 'JV-Agent REV&COST Adj', 'JV-Agent totalvalue Adj')))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE = 'E05') AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE IN('Z1', 'Z2', 'Z3')) AND(PL_E100155.PROJ_TYPE_CODE = '01') AND(PL_E100147.CN_NAME <> 'JV-ADJ 557 WITH B CODE') AND((((((((PL_E100119.LVL1_ACCOUNT_CODE IN('501', '503', '506', '512')) OR(PL_E100119.GROUP_ACCOUNT_CODE = '5980406')) AND((PL_E100121.PROD_CLASS_FLAG = '0') OR(PL_E100122.PROD_CLASS_FLAG = '0'))) OR((PL_E100119.LVL1_ACCOUNT_CODE IN('504', 'SVC')) OR(PL_E100119.LVL2_ACCOUNT_CODE IN('55107', '57702', '57703', '58303')) OR(PL_E100119.GROUP_ACCOUNT_CODE IN('5980407', '5825107', '5827702', '5827703', 'C501'))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E01', 'E03', 'E05', 'E06', 'E08', 'E09', 'E10', 'E11', 'E02', 'E04', 'E07', 'E12')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE = 'Z4') AND((PL_E100155.PROJ_TYPE_CODE <> '02') OR(PL_E100155.PROJ_NUM IN('9000000')))) OR((PL_E100119.ACCOUNT_EXPENSE_CATG_CODE IN('E02', 'E04', 'E07', 'E12', 'E05', 'E09', 'E10')) AND(PL_E100134.DEPT_EXPENSE_TYPE_CODE IN('Z1', 'Z2', 'Z3')) AND(PL_E100155.PROJ_TYPE_CODE = '01'))) AND((PL_E100119.GROUP_ACCOUNT_CODE <> 'EXP5555')))) AND(PL_E100119.LVL2_ACCOUNT_CODE <> '58303') AND(PL_E100155.PROJ_TYPE_CODE = '01')))))

 AND T.PERIOD_ID >= 202208

 AND T.PERIOD_ID <= 202208

    ) A

)

-- 对分布列做汇总求和，查找分布列值重复次数最多的值

SELECT

 record_seq_num, cnt

FROM (

 SELECT record_seq_num, count(1) AS cnt

 FROM t

 GROUP BY record_seq_num HAVING count(1) > 10000

)

ORDER BY cnt

LIMIT 10

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