测试merge效率

测试说明：

MERGE是oracle提供的一种特殊的sql语法，非常适用于数据同步场景，即： （把A表数据插到B表，如果B表存在相同主键的记录则使用A表数据对B表进行更新） 数据同步的常规做法是先尝试插入，插入失败再进行更新，MERGE比这种常规做法效率高很多。 （特别是A与B表基本一致，同步时主键冲突比较多的情况，效率能相差10倍以上）

为了验证MERGE效率，我建了两张表，tab_test_C（初始化生成50000条记录）和tab_test_Q（初始化从tab_test_C生成40000条记录）， 写了两个plsql脚本，分别将tab_test_C的数据同步到tab_test_Q，看它们效率区别。

第一个脚本使用merge语法，第二个脚本使用常规先插入，出现主键冲突的操作。

测试结果：
 使用merge语法的脚本同步数据耗时0.04秒，使用常规操作耗时14.77秒，效率差369倍

测试脚本：

SET SERVEROUTPUT ON
-- 启动计时 以便观察脚本执行时间
SET TIMING ON
SET TIME ON

-- 数据初始化 
DROP TABLE tab_test_C;
CREATE TABLE tab_test_C
(
    C1 VARCHAR2(512),
    C2 VARCHAR2(512),
    C3 VARCHAR2(512),
    C4 VARCHAR2(512),
    C5 VARCHAR2(512),
    C6 VARCHAR2(512),
    C7 VARCHAR2(512),
    C8 VARCHAR2(512),
    C9 VARCHAR2(512),
    C10 VARCHAR2(512)
);

DECLARE
    v_total number;
BEGIN
    v_total := 0;
    LOOP
        EXIT WHEN v_total >= 50000;
        for cur in (select owner, object_name, subobject_name, object_id, data_object_id, object_type,
            created, last_ddl_time, timestamp from all_objects where rownum < 101)
        loop
            insert into tab_test_C values (cur.owner, cur.object_name, cur.subobject_name,
            cur.object_id, cur.data_object_id,
            cur.object_type, cur.created,
            cur.last_ddl_time, cur.timestamp, v_total);
            v_total := v_total + 1;
        end loop;
    END LOOP;
    COMMIT;
END;
/

-- 建唯一索引
select count(1) from tab_test_C;
create UNIQUE INDEX uid_test_c_1 on tab_test_C(C10);

--初始化tab_test_Q表数据，先从tab_test_C生成同步40000条数据，剩下10000条数据使用脚本同步过来
DROP TABLE tab_test_Q;
CREATE TABLE tab_test_Q AS SELECT * FROM tab_test_C where rownum < 40001;
create UNIQUE INDEX uid_test_q_1 on tab_test_Q(C10);
-- 验证数据未同步成功 此时记录数差1000
select count(*) from tab_test_Q;

-- 使用merge语法同步tab_test_C的数据到tab_test_Q
DECLARE
    CURSOR cur is select * from tab_test_C;
    type mergeArray_t is table of tab_test_C % ROWTYPE index by BINARY_INTEGER;
    mergeArray mergeArray_t;
BEGIN
    OPEN cur;
    LOOP
        EXIT WHEN cur % NOTFOUND;
        FETCH cur bulk collect into mergeArray LIMIT 16; -- 每次限十几条记录，不要占用太多内存 这个数字调大点效率会更高
        BEGIN
            FORALL rw IN 1 .. mergeArray.count
                MERGE INTO tab_test_Q A
                USING (SELECT mergeArray(rw).C1 C1, mergeArray(rw).C2 C2, mergeArray(rw).C3 C3, mergeArray(rw).C4 C4,
                    mergeArray(rw).C5 C5, mergeArray(rw).C6 C6, mergeArray(rw).C7 C7, mergeArray(rw).C8 C8,
                    mergeArray(rw).C9 C9, mergeArray(rw).C10 C10 FROM DUAL) B
                ON (A.C10 = B.C10)
                WHEN MATCHED THEN
                    UPDATE SET A.C1 = mergeArray(rw).C1, A.C2 = mergeArray(rw).C2, A.C3 = mergeArray(rw).C3,
                        A.C4 = mergeArray(rw).C4, A.C5 = mergeArray(rw).C5,
                        A.C6 = mergeArray(rw).C6, A.C7 = mergeArray(rw).C7, A.C8 = mergeArray(rw).C8,
                        A.C9 = mergeArray(rw).C9
                WHEN NOT MATCHED THEN
                    INSERT (C1, C2, C3, C4, C5, C6, C7, C8, C9, C10) VALUES(mergeArray(rw).C1, mergeArray(rw).C2,
                        mergeArray(rw).C3, mergeArray(rw).C4, mergeArray(rw).C5, mergeArray(rw).C6,
                        mergeArray(rw).C7, mergeArray(rw).C8, mergeArray(rw).C9, mergeArray(rw).C10);
            -- DBMS_OUTPUT.PUT_LINE(mergeArray.count);
        EXCEPTION
            WHEN OTHERS THEN
                    DBMS_OUTPUT.PUT_LINE('error1');
        END;
    END LOOP;
    CLOSE cur;
    COMMIT;
END;
/

--耗时0.04秒
-- 验证数据同步成功 
select count(*) from tab_test_Q;

--初始化tab_test_Q表数据，先从tab_test_C生成同步40000条数据，剩下10000条数据使用脚本同步过来
DROP TABLE tab_test_Q;
CREATE TABLE tab_test_Q AS SELECT * FROM tab_test_C where rownum < 40001;
create UNIQUE INDEX uid_test_q_1 on tab_test_Q(C10);
-- 验证数据未同步成功 此时记录数差1000
select count(*) from tab_test_Q;

-- 使用常规语法同步tab_test_C的数据到tab_test_Q
BEGIN
    for cur in (select * from tab_test_C)
    LOOP
        BEGIN
            INSERT INTO tab_test_Q(C1, C2, C3, C4, C5, C6, C7, C8, C9, C10)
            VALUES(cur.C1, cur.C2, cur.C3, cur.C4, cur.C5, cur.C6, cur.C7, cur.C8, cur.C9, cur.C10);
        EXCEPTION
            WHEN DUP_VAL_ON_INDEX THEN --唯一索引冲突时更新
                UPDATE tab_test_Q SET C1 = cur.C1, C2 = cur.C2, C3 = cur.C3, C4 = cur.C4, C5 = cur.C5, C6 = cur.C6, C7 = cur.C7, C8 = cur.C8, C9 = cur.C9
                WHERE C10 = cur.C10;
            WHEN OTHERS THEN
                    DBMS_OUTPUT.PUT_LINE('error1');
        END;
    END LOOP;
    COMMIT;
END;
/

--耗时14.77秒
-- 验证数据同步成功
select count(*) from tab_test_Q;