标签：说明 net access 连接 函数 代码优化 方式 执行 row
案例说明
在月底进行代码优化检查过程中。在SQL检查过程之执行次数最多的SQL。发现SQL_ID为grk7dk5amf5m7和gzzzkzbfg8j2m 在半个小时内产生大约分别15亿次执行。逻辑读也有15G
其实SQL本身很简单；是一个自定义的分割函数。
原SQL
select to_char(a.logintime, ‘yyyymmdd‘), to_char(a.logintime, ‘HH24‘), 2552, substr(a.qn, 5, 4) ad, regexp_substr(a.qn, ‘[^_]+‘, 1, 2) channelid, a.account, sysdate from ssdk_acc_login a where to_char(a.logintime, ‘yyyymmdd‘) = ‘20170728‘ and splitstr(a.qn, 2, ‘_‘) in (select cid from tbl_channel where channel_tag like ‘广点通%‘);
该SQL的执行计划
Execution Plan ---------------------------------------------------------- Plan hash value: 2543353618 ----------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 7236 | 558K| 2445 (1)| 00:00:30 | | 1 | VIEW | VM_NWVW_2 | 7236 | 558K| 2445 (1)| 00:00:30 | | 2 | HASH UNIQUE | | 7236 | 607K| 2445 (1)| 00:00:30 | |* 3 | HASH JOIN | | 7236 | 607K| 2444 (1)| 00:00:30 | |* 4 | TABLE ACCESS FULL | TBL_CHANNEL | 154 | 2772 | 5 (0)| 00:00:01 | | 5 | TABLE ACCESS BY INDEX ROWID| SSDK_ACC_LOGIN | 95232 | 6324K| 2438 (1)| 00:00:30 | |* 6 | INDEX RANGE SCAN | IND_SDK_LOGIN_TIME | 95232 | | 670 (1)| 00:00:09 | ----------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 3 - access("CID"="SPLITSTR"(INTERNAL_FUNCTION("A"."QN"),2,‘_‘)) 4 - filter("CHANNEL_TAG" LIKE ‘广点通%‘) 6 - access(TO_CHAR(INTERNAL_FUNCTION("LOGINTIME"),‘yyyymmdd‘)=‘20170728‘) Statistics ---------------------------------------------------------- 152770 recursive calls 1833240 db block gets 307000 consistent gets 0 physical reads 0 redo size 1465885 bytes sent via SQL*Net to client 20225 bytes received via SQL*Net from client 1793 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 26867 rows processed
从执行计划上来看。存在有152770递归调用和约200M的逻辑读。但是返回的行数只有2万条。逻辑读跟返回的行数严重失调。本身表ssdk_acc_login是一个大表。
对有经验的人来说；产生大量的递归条用；很容易看出问题跟自定义函数SPLITSTR有关。
通过等价改下SQL
select to_char(a.logintime, ‘yyyymmdd‘), to_char(a.logintime, ‘HH24‘), 2552, substr(a.qn, 5, 4) ad, regexp_substr(a.qn, ‘[^_]+‘, 1, 2) channelid, a.account, sysdate from ssdk_acc_login a where to_char(a.logintime, ‘yyyymmdd‘) = ‘20170728‘ and regexp_substr(a.qn,‘[^_]+‘,1,2) in (select cid from tbl_channel where channel_tag like ‘广点通%‘);
该SQL 的执行计划
Execution Plan ---------------------------------------------------------- Plan hash value: 2829062945 --------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 47 | 3478 | 2443 (1)| 00:00:30 | | 1 | NESTED LOOPS | | 47 | 3478 | 2443 (1)| 00:00:30 | | 2 | SORT UNIQUE | | 154 | 2772 | 5 (0)| 00:00:01 | |* 3 | TABLE ACCESS FULL | TBL_CHANNEL | 154 | 2772 | 5 (0)| 00:00:01 | |* 4 | TABLE ACCESS BY INDEX ROWID| SSDK_ACC_LOGIN | 47 | 2632 | 2437 (1)| 00:00:30 | |* 5 | INDEX RANGE SCAN | IND_SDK_LOGIN_TIME | 95232 | | 669 (1)| 00:00:09 | --------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 3 - filter("CHANNEL_TAG" LIKE ‘广点通%‘) 4 - filter("CID"= REGEXP_SUBSTR ("A"."QN",‘[^_]+‘,1,2)) 5 - access(TO_CHAR(INTERNAL_FUNCTION("LOGINTIME"),‘yyyymmdd‘)=‘20170728‘) Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 214489 consistent gets 0 physical reads 556 redo size 1345632 bytes sent via SQL*Net to client 20324 bytes received via SQL*Net from client 1802 SQL*Net roundtrips to/from client 1 sorts (memory) 0 sorts (disk) 27004 rows processed
执行计划
与之前的SQL的执行计划相比；代价相差无几。连接方式由hash连接改为NESTED LOOPS
统计信息：
递归调用：前面是152770次。现在是0次。
逻辑读： 前面是约200M。现在是约20M。相差10倍。
redo日志。前面不产生。现在产生556kb。影响不大。
排序： 前面不产生；现在产生排序。此服务器专用于oracle。内存48G。影响不大。
综上所述：用正则函数regexp_substr来替换 自定义函数splitstr更好。尽量避免使用自定义函数进行大量运算
标签：说明 net access 连接 函数 代码优化 方式 执行 row
原文地址：http://www.cnblogs.com/lottu/p/7250271.html
