数据结构index是什么(数据库索引可以用hash实现吗)-柠檬ai自媒体

这篇文章给大家分享的是有关数据库中计划_散列_值有什么用的内容。小编觉得挺实用的，因此分享给大家做个参考，一起跟随小编过来看看吧。

plan_hash_value判断sql的访问路径是否改变的主要方法是：v$sql.plan_hash_value的值是否改变。如果不同的sql语句含有相同的实验：---创建表deptSQL create table dept as select * from scott.dept;Table created.---执行2条sql查询dept表http://

;                     l_execution_enabled', 'false') NO_PARALLEL_INDEX(SAMPLESUB) NO_SQL_TUNE */ NVL(SUM(C1),0), NVL(SUM(C
                                                         2),0) FROM (SELECT /*+ NO_PARALLEL("DEPT") FULL("DEPT") NO_PARALLEL_INDEX("DEPT") */ 1 AS C1, 1 AS C
                                                         2 FROM "SYS"."DEPT" "DEPT") SAMPLESUB

0000000061211A40 2958346034            0      2657262937 select ADDRESS, HASH_VALUE, SQL_ID, PLAN_HASH_VALUE, CHILD_ADDRESS,          CHILD_NUMBER, TIMESTAM
                                                         P, OPERATION,                                         OPTIONS, OBJECT_NODE, OBJECT#, OBJECT_OWNER, O
                                                         BJECT_NAME,                    OBJECT_ALIAS, OBJECT_TYPE, OPTIMIZER,
                                                                 ID, PARENT_ID, DEPTH, POSITION, SEARCH_COLUMNS, COST, CARDINALITY,           BYTES, OTHER_TA
                                                         G, PARTITION_START, PARTITION_STOP, PARTITION_ID,             OTHER, DISTRIBUTION, CPU_COST, IO_COST
                                                         , TEMP_SPACE,                          ACCESS_PREDICATES, FILTER_PREDICATES, PROJECTION, TIME, QBLOC
                                                         K_NAME,         REMARKS, OTHER_XML                                                           from GV
                                                         $SQL_PLAN                                                             where inst_id = USERENV('Insta
                                                         nce')

000000008B5D3908 3410315986 0 903671040 select address,hash_value,child_number,plan_hash_value,sql_text from v$sql where sql_text like '%DEP
T%'

000000008B626668 3145184715            0       315352865 SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE NO_PARALLEL(SAMPLESUB) opt_param('paralle
                                                         l_execution_enabled', 'false') NO_PARALLEL_INDEX(SAMPLESUB) NO_SQL_TUNE */ NVL(SUM(C1),0), NVL(SUM(C
                                                         2),0) FROM (SELECT /*+ IGNORE_WHERE_CLAUSE NO_PARALLEL("DEPT") FULL("DEPT") NO_PARALLEL_INDEX("DEPT"
                                                         ) */ 1 AS C1, CASE WHEN "DEPT"."DEPTNO"=10 THEN 1 ELSE 0 END AS C2 FROM "SYS"."DEPT" "DEPT") SAMPLES
                                                         UB

---通过v$sql_plan查询执行计划
SQL> SELECT operation, options, object_name, cost FROM v$sql_plan WHERE address ='000000008B589B40' and HASH_VALUE='3749466620';

SQL>
SQL> SELECT operation, options, object_name, cost FROM v$sql_plan WHERE address ='000000008B626668' and HASH_VALUE='3145184715';

--对表dept做修改，增加索引
SQL> create index idx_dept_deptno on dept(deptno);

Index created.

---再次查看
SQL> select address,hash_value,child_number,plan_hash_value,sql_text from v$sql where sql_text like '%DEPT%';

ADDRESS          HASH_VALUE CHILD_NUMBER PLAN_HASH_VALUE SQL_TEXT
---------------- ---------- ------------ --------------- ----------------------------------------------------------------------------------------------------
000000008B589B40 3749466620            0       315352865 SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE NO_PARALLEL(SAMPLESUB) opt_param('paralle
                                                         l_execution_enabled', 'false') NO_PARALLEL_INDEX(SAMPLESUB) NO_SQL_TUNE */ NVL(SUM(C1),0), NVL(SUM(C
                                                         2),0) FROM (SELECT /*+ NO_PARALLEL("DEPT") FULL("DEPT") NO_PARALLEL_INDEX("DEPT") */ 1 AS C1, 1 AS C
                                                         2 FROM "SYS"."DEPT" "DEPT") SAMPLESUB

000000008B5D3908 3410315986 0 903671040 select address,hash_value,child_number,plan_hash_value,sql_text from v$sql where sql_text like '%DEP
T%'

000000008E0A74E0 1470990285            0               0 LOCK TABLE "DEPT" IN SHARE MODE NOWAIT
000000008B626668 3145184715            0       315352865 SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE NO_PARALLEL(SAMPLESUB) opt_param('paralle
                                                         l_execution_enabled', 'false') NO_PARALLEL_INDEX(SAMPLESUB) NO_SQL_TUNE */ NVL(SUM(C1),0), NVL(SUM(C
                                                         2),0) FROM (SELECT /*+ IGNORE_WHERE_CLAUSE NO_PARALLEL("DEPT") FULL("DEPT") NO_PARALLEL_INDEX("DEPT"
                                                         ) */ 1 AS C1, CASE WHEN "DEPT"."DEPTNO"=10 THEN 1 ELSE 0 END AS C2 FROM "SYS"."DEPT" "DEPT") SAMPLES
                                                         UB

----再次执行上述相同的2条sql
SQL> select deptno,dname from dept where deptno=10;

DEPTNO DNAME
---------- --------------
10 ACCOUNTING

SQL> select deptno,dname from dept;

    DEPTNO DNAME
---------- --------------
        10 ACCOUNTING
        20 RESEARCH
        30 SALES
        40 OPERATIONS

---查询v$sql下的address,hash_value,child_number,plan_hash_value,sql_text
SQL> select address,hash_value,child_number,plan_hash_value,sql_text from v$sql where sql_text like '%DEPT%';

000000008B5D3908 3410315986 0 903671040 select address,hash_value,child_number,plan_hash_value,sql_text from v$sql where sql_text like '%DEP
T%'

00000000613ACE30 1756886759            0      2570986044 SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS opt_param('parallel_execution_enabled', 'false') NO_PARALLEL(
                                                         SAMPLESUB) NO_PARALLEL_INDEX(SAMPLESUB) NO_SQL_TUNE */ NVL(SUM(C1),0), NVL(SUM(C2),0), NVL(SUM(C3),0
                                                         ) FROM (SELECT /*+ NO_PARALLEL("DEPT") INDEX("DEPT" IDX_DEPT_DEPTNO) NO_PARALLEL_INDEX("DEPT") */ 1
                                                         AS C1, 1 AS C2, 1 AS C3 FROM "SYS"."DEPT" "DEPT" WHERE "DEPT"."DEPTNO"=10 AND ROWNUM <= 2500) SAMPL
                                                         ESUB

6 rows selected.

---再次查看执行计划
SQL> SELECT operation, options, object_name, cost FROM v$sql_plan WHERE address ='000000008B589B40' and HASH_VALUE='3749466620';

SQL> SELECT operation, options, object_name, cost FROM v$sql_plan WHERE address ='000000008B626668' and HASH_VALUE='3145184715';

SQL> SELECT operation, options, object_name, cost FROM v$sql_plan WHERE address ='00000000613ACE30' and HASH_VALUE='1756886759';

OPERATION                                                    OPTIONS                                                      OBJECT_NAME                          COST
------------------------------------------------------------ ------------------------------------------------------------ ------------------------------ ----------
SELECT STATEMENT                                                                                                                                                  1
SORT                                                         AGGREGATE
VIEW                                                                                                                                                              1
COUNT                                                        STOPKEY
INDEX                                                        RANGE SCAN                                                   IDX_DEPT_DEPTNO                         1
最终发现执行计划已经改变，所以可以根据plan_hash_value值是否变化可知该sql语句的执行计划是否改变

通过v$sql视图的plan_hash_value值可以很方便的知道，该sql语句的执行计划是否改变，
通常我们的做法是分别将v$sql,v$sql_hash做两份快照，隔段时间后再做段快照，然后将其进行比较，查看是否有sql的执行计划已经改变。

感谢各位的阅读！关于“数据库中plan_hash_value有什么用”这篇文章就分享到这里了，希望

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数据结构index是什么(数据库索引可以用hash实现吗)

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