《avh--新一代智能sql语句优化技术课件》由会员分享，可在线阅读，更多相关《avh--新一代智能sql语句优化技术课件（46页珍藏版）》请在金锄头文库上搜索。
1、DM10:Sybase SQL Expert 12.5 新一代智能SQL语句优化技术 The New Generation of Intelligent SQL Tuning Technology,杜伟业 ( Richard To) R 技术总监 灵高科研有限公司,什么是反应时间,1/10秒是用户认为系统能够立即反应的极限,1 秒是用户觉得没有被中断的极限,10秒是用户能将注意力继续集中在与计算机的对话上的时间极限,引用自Jakob Nielsen 的 “Usability Engineering” 第五章 (Morgan Kaufmann, San Francisco出版),我们可以关注的地
2、方,可调整的部分: 硬件 操作系统 数据库 网络 应用程序,许多人在试图提高数据库应用程序性能时只将注意力放在了前三项：硬件、操作系统、数据库,数据库系统各部分对性能的影响,应用程序,数据库,操作系统,硬件,网络,Wrong Focus,应用程序,其它,最 少 60% 的 数 据 库 性 能 问 题 是 由 应 用 程 序 引 起 的,性能的挑战,我们可以优化什么?,数据库设计问题 编程问题 索引问题 SQL问题,什么是 SQL ? (结构化查询语言),访问和更新数据 对应用程序的性能产生最重大的影响 SQL语句消耗70%到90%的数据库系统资源 SQL语句可以有多种写法 易学，但难以精通 需
3、要考虑在数据和系统环境变化后仍能达到最佳化,数据库是如何处理SQL语句的?,SQL,数据库的优化器是如何工作的?,内部重写并产生多种执行计划,执行计划1,执行计划2,执行计划3,成本估计,执行计划1 成本=1000,执行计划2 成本=3000,执行计划3 成本= 500,执行,优化器说明,什么是执行计划 SQL语法如何影响优化器的决定,什么是SQL优化?,解决这个问题的传统途径,执行计划,SET SHOWPLAN ON GO SELECT * FROM EMPLOYEE WHERE EMP_ID 73712 GO SET SHOWPLAN OFF GO,QUERY PLAN FOR STATE
4、MENT 1 (at line 1). STEP 1 The type of query is SELECT. FROM TABLE EMPLOYEE Nested iteration. Table Scan. Forward scan. Positioning at start of table. Using I/O Size 2 Kbytes for data pages. With LRU Buffer Replacement Strategy for data pages. Total estimated I/O cost for statement 1 (at line 1): 20
5、600.,iSQL,IO和时间统计信息,SET STATISTICS IO ON GO SET STATISTICS TIME ON GO SELECT * FROM EMPLOYEE WHERE EMP_ID 73712 GO SET STATISTICS IO OFF GO SET STATISTICS TIME OFF GO,iSQL,Server Message: Number 3631, Severity 10 Line 1: Total actual I/O cost for this command: 0. Total writes for this command: 0 Ser
6、ver Message: Number 3631, Severity 10 Line 1: Total actual I/O cost for this command: 0. Total writes for this command: 0 Execution Time 0. SQL Server cpu time: 0 ms. SQL Server elapsed time: 3614 ms. Parse and Compile Time 0. SQL Server cpu time: 0 ms. Table: EMPLOYEE scan count 1, logical reads: (
7、regular=1030 apf=0 total=1030), physical reads: (regular=0 apf=0 total=0), apf IOs used=0 Server Message: Number 3631, Severity 10 Line 1: Total actual I/O cost for this command: 2060. Total writes for this command: 0 Execution Time 16. SQL Server cpu time: 1600 ms. SQL Server elapsed time: 7730 ms.
8、 (18371 rows affected) Parse and Compile Time 0. SQL Server cpu time: 0 ms. Execution Time 0. SQL Server cpu time: 0 ms. SQL Server elapsed time: 0 ms. Parse and Compile Time 0. SQL Server cpu time: 0 ms.,Traceon,DBCC TRACEON (3604, 302, 310) GO SELECT * FROM EMPLOYEE WHERE EMP_ID 73712 GO,iSQL,Begi
9、nning selection of qualifying indexes for table EMPLOYEE, varno = 0, objectid 1593824790. The table (Allpages) has 18373 rows, 1030 pages, Data Page Cluster Ratio 0.998890 Table scan cost is 18373 rows, 1030 pages, using no data prefetch (size 2K I/O), in data cache default data cache (cacheid 0) wi
10、th LRU replacement Selecting best index for the SEARCH CLAUSE: EMPLOYEE.EMP_ID 73712.000000 Estimated selectivity for EMP_ID, selectivity = 0.999946. Estimating selectivity of index EMPLOYEE_1961957491, indid 1 scan selectivity 0.999946, filter selectivity 0.999946 18372 rows, 1032 pages, index heig
11、ht 2, Data Row Cluster Ratio 1.000000, Index Page Cluster Ratio 0.000000, Data Page Cluster Ratio 0.998890 ,使用 EXIST 还是 IN？ SELECT * FROM A WHERE A.CITY IN (SELECT B.CITY FROM B) SELECT * FROM A WHERE EXISTS (SELECT X FROM B WHERE B.CITY = A.CITY),EXIST or IN,表连接与子查询,通情况下表连接(Table join)要好过子查询(sub-qu
12、ery) 源语句 SELECT * FROM A WHERE A.CITY IN (SELECT B.CITY FROM B) 重写后 SELECT A.* FROM A, B WHERE A.CITY = B.CITY /* if B.CITY is unique in B */,如果你确实知道问题所在，可以强制使用一个特殊的表操纵路径( driving path )。 源语句 SELECT * FROM A, B WHERE A.STATE = B.STATE 重写后的语句 /* 禁止使用B的索引来改变表操纵路径 (B drive A) */ SELECT * FROM A, B WHER
13、E A.STATE = ISNULL(B.STATE,B.STATE),Joins Change Table Driving Path,要使用索引就不能在该索引字段上进行操作 源语句 /* A.key1上的索引被使用*/ SELECT * FROM A WHERE A.Key1 = ver1 AND A.Key2 = ver2 重写后 /* 禁止使用字段A.key1上的索引，使用字段A.Key2上的索引*/ SELECT * FROM A WHERE ISNULL(A.Key1, A.key1) = ver1 AND A.Key2 = ver2,Use Indexes,学习使用强制选项(For
14、ces Options) SET FORCEPLAN ON INDEX hint PARALLEL hint SET SORT_MERGE ON SET JTC ON SET TABLE COUNT,Forces,使用FORCEPLAN 强制选项强制使用特殊的表操纵路径 (driving path)。 原来的方法 /*禁止使用B的索引来改变表操纵路径 (B drive A)*/ SELECT * FROM A, B WHERE A.STATE = ISNULL(B.STATE,B.STATE) 用 FORCEPLAN重写后 SET FORCEPLAN ON GO SELECT * FROM B
15、, A WHERE A.STATE = B.STATE GO,Joins Change Table Driving Path,强制索引(Force Index),SELECT * FROM EMPLOYEE WHERE EMP_ID 73712,Force Index,备注： 仅在事先知道使用使用索引 x 将会较快的情况下采用,(INDEX EMP_ID_INX),QUERY PLAN FOR STATEMENT 1 (at line 1). STEP 1 The type of query is SELECT. FROM TABLE EMPLOYEE Nested iteration. Ta
16、ble Scan. Forward scan. Positioning at start of table. Using I/O Size 2 Kbytes for data pages. With LRU Buffer Replacement Strategy for data pages. Total estimated I/O cost for statement 1 (at line 1): 20600.,QUERY PLAN FOR STATEMENT 1 (at line 1). STEP 1 The type of query is SELECT. FROM TABLE EMPLOYEE Nested iteration. Index : EMP_ID_INX Forward scan. Positioning by key. Keys are: EMP_ID ASC Using I/O Size 2 Kby
