达梦数据库查询较慢的快速诊断及优化

SELECT TOP 20 START_TIME,TIME_USED/1000 TIME_USED,TOP_SQL_TEXT FROM V$SQL_HISTORY ORDER BY TIME_USED DESC;
SELECT * FROM V$SYSTEM_LONG_EXEC_SQLS ORDER BY EXEC_TIME DESC;

SELECT
        DS.SESS_ID "被阻塞的会话ID",
        DS.SQL_TEXT "被阻塞的SQL",
        DS.TRX_ID "被阻塞的事务ID",
        (CASE L.LTYPE WHEN 'OBJECT' THEN '对象锁' WHEN 'TID' THEN '事务锁' END CASE ) "被阻塞的锁类型",
        DS.CREATE_TIME "开始阻塞时间",
        SS.SESS_ID "占用锁的会话ID",
        SS.SQL_TEXT "占用锁的SQL",
        SS.CLNT_IP "占用锁的IP",
        L.TID "占用锁的事务ID"
FROM
        V$LOCK L
LEFT JOIN V$SESSIONS DS
ON
        DS.TRX_ID = L.TRX_ID
LEFT JOIN V$SESSIONS SS
ON
        SS.TRX_ID = L.TID
WHERE
        L.BLOCKED = 1;

select
      name 缓冲池名称,
      sum(page_size)*sf_get_page_size 缓冲池大小_G,
      sum(rat_hit) /count(*) 命中率
from
      v$bufferpool
group by name;

EXPLAIN SELECT * FROM your_table WHERE your_conditions;

SELECT id, name FROM users WHERE status = 1;  -- 好
SELECT * FROM users WHERE status = 1;         -- 差

CREATE INDEX idx_users_status ON users(status);

SELECT * FROM orders WHERE DATE_FORMAT(create_time, '%Y-%m') = '2024-01';  -- 差
SELECT * FROM orders WHERE create_time >= '2024-01-01' AND create_time < '2024-02-01';  -- 好

SELECT * FROM table1 WHERE EXISTS (
    SELECT 1 FROM table2 WHERE table1.id = table2.id
);

CALL SP_TAB_STAT_INIT('SCHEMA_NAME', 'TABLE_NAME');

CALL SP_DB_STAT_INIT('SCHEMA_NAME');

CALL SP_COL_STAT_INIT('SCHEMA_NAME', 'TABLE_NAME', 'COLUMN_NAME');

DBMS_STATS.GATHER_SCHEMA_STATS('DB_TEST', 100, TRUE, 'FOR ALL COLUMNS SIZE AUTO');

DBMS_STATS.GATHER_TABLE_STATS('username', 'table_name', null, 100, TRUE, 'FOR ALL COLUMNS SIZE AUTO', cascade => true, degree => 8);

drop table if exists my_tab_stats;
create table my_tab_stats(table_name varchar2(100),owner varchar2(100),stat_flag varchar2(5),begin_time timestamp,end_time timestamp);
insert into my_tab_stats(table_name,owner) select table_name,owner from dba_tables where owner in ('OA');
update my_tab_stats set stat_flag = 0;
commit;
begin
    for tb in (select rowid,table_name,owner from my_tab_stats where stat_flag = 0 ) 
	loop
        update my_tab_stats set begin_time=sysdate where my_tab_stats.table_name=tb.table_name and my_tab_stats.owner=tb.owner;
        dbms_stats.gather_table_stats(tb.owner,tb.table_name,null,100,true,'FOR ALL COLUMNS SIZE AUTO',cascade => true, degree => 8);
        update my_tab_stats set stat_flag = 1,end_time=sysdate where my_tab_stats.table_name = tb.table_name and my_tab_stats.owner=tb.owner;
        commit;
    end loop;
end;

– 对大表进行分区
CREATE TABLE sales (
sale_id INT,
sale_date DATE,
amount DECIMAL(10,2)
)
PARTITION BY RANGE(sale_date)
(
PARTITION p2023 VALUES LESS THAN (‘2024-01-01'),
PARTITION p2024 VALUES LESS THAN (‘2025-01-01')
);

CREATE MATERIALIZED VIEW mv_sales_summary
REFRESH COMPLETE ON DEMAND
AS 
SELECT customer_id, SUM(amount) as total_amount,
       COUNT(*) as order_count
FROM sales 
GROUP BY customer_id;