Oracle主键与复合主键的性能分析

Oracle主键与复合主键的性能分析


总结：
1、主键和复合主键，查询性能相同（索引高度相同，恰当的运用索引）。
2、 主键和复合主键，(update,insert)性能不同 (因为复合主键会用更多的块来创建索引，所以update,insert性能低)


实验思路：
1、 建立实验表，及主键，联合2个主键，联合3个主键
2、 查看索引的结构
3、查看条件相同的，执行计划（来确定主键和复合主键的效率）


一、 建立实验表；test1为单主键为1个column，test2为联合主键2个columns，test3为联合主键3个columns
SQL> create table test1(a number,b number,c number,primary key(a));

Table created.

SQL> create table test2(a number,b number,c number,primary key(a,b));

Table created.

SQL> create table test3(a number,b number,c number,primary key(a,b,c));

Table created.

二、 查看索引的结构
1、先查看一下建立的表对应的索引
SQL> select index_name,table_name from user_indexes;

INDEX_NAME TABLE_NAME
------------------------------ ------------------------------
SYS_C005198 TEST1
SYS_C005199 TEST2
SYS_C005200 TEST3

2、写个储存过程来给实验表插入数据
begin
for i in 1..10000 loop
insert into test1 values(i,i+1,i+2);
commit;
end loop;
end;


Test1
SQL> analyze index SYS_C005198 validate structure;

Index analyzed.

SQL> select HEIGHT,BLOCKS,BR_BLKS,LF_BLKS,LF_ROWS,DEL_LF_ROWS from index_stats ;

HEIGHT BLOCKS BR_BLKS LF_BLKS LF_ROWS DEL_LF_ROWS
---------- ---------- ---------- ---------- ---------- -----------
2 24 1 18 10000 0
Test2
SQL> analyze index SYS_C005199 validate structure;

Index analyzed.

SQL> select HEIGHT,BLOCKS,BR_BLKS,LF_BLKS,LF_ROWS,DEL_LF_ROWS from index_stats ;


HEIGHT BLOCKS BR_BLKS LF_BLKS LF_ROWS DEL_LF_ROWS
---------- ---------- ---------- ---------- ---------- -----------
2 32 1 23 10000 0
Test3
SQL> analyze index SYS_C005200 validate structure;

Index analyzed.

SQL> select HEIGHT,BLOCKS,BR_BLKS,LF_BLKS,LF_ROWS,DEL_LF_ROWS from index_stats ;

HEIGHT BLOCKS BR_BLKS LF_BLKS LF_ROWS DEL_LF_ROWS
---------- ---------- ---------- ---------- ---------- -----------
2 40 1 28 10000 0

总结：根据B-TREE索引的结构特点。说明主键和联合主键， 同样的数据联合主键需要更多的资源来维护索引。（联合主键索引因为用了更多的块，所以update,insert 会比主键索引慢一些。至于查询下面研究）

三、 查看相同情况下，主键的效率。

1、 语句都让其走INDEX UNIQUE SCAN ，看看效率：


Test1
SQL> select a from test1 where a=5555;

A
----------
5555


Execution Plan
----------------------------------------------------------
Plan hash value: 2716871853

--------------------------------------------------------------------------------
-

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|

--------------------------------------------------------------------------------
-

| 0 | SELECT STATEMENT | | 1 | 13 | 1 (0)| 00:00:01
|

|* 1 | INDEX UNIQUE SCAN| SYS_C005198 | 1 | 13 | 1 (0)| 00:00:01
|

--------------------------------------------------------------------------------
-


Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("A"=5555)


Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
405 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
Test2
SQL> select a,b from test2 where a=5555 and b=5556;

A B
---------- ----------
5555 5556


Execution Plan
----------------------------------------------------------
Plan hash value: 3210951477

--------------------------------------------------------------------------------
-

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|

--------------------------------------------------------------------------------
-

| 0 | SELECT STATEMENT | | 1 | 26 | 1 (0)| 00:00:01
|

|* 1 | INDEX UNIQUE SCAN| SYS_C005199 | 1 | 26 | 1 (0)| 00:00:01
|

--------------------------------------------------------------------------------
-


Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("A"=5555 AND "B"=5556)


Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
460 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
Test3
SQL> select a,b,c from test3 where a=5555 and b=5556 and c=5557;

A B C
---------- ---------- ----------
5555 5556 5557


Execution Plan
----------------------------------------------------------
Plan hash value: 1852305570

--------------------------------------------------------------------------------
-

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|

--------------------------------------------------------------------------------
-

| 0 | SELECT STATEMENT | | 1 | 39 | 1 (0)| 00:00:01
|

|* 1 | INDEX UNIQUE SCAN| SYS_C005200 | 1 | 39 | 1 (0)| 00:00:01
|

--------------------------------------------------------------------------------
-


Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("A"=5555 AND "B"=5556 AND "C"=5557)


Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
515 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed

分析：通过执行SQL走INDEX UNIQUE SCAN索引的情况，分析执行计划得到的结果是主键和联合主键性能相同：

（我们关注的：
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
消耗一致和COST消耗一致。）

总结：主键和联合主键，应用B-tree索引的情况下，如果我们的索引高度相同,且正确的应用索引。这样的情况下我们查询性能是相同的。


欢迎大家给与纠正错误，共同提升！

参考：
Oracle主键与复合主键的性能分析-lovehewenyu-ITPUB博客
http://blog.itpub.net/26442936/viewspace-734960
讨论数据库中复合键的优缺点-CSDN论坛-CSDN.NET-中国最大的IT技术社区
http://bbs.csdn.net/topics/90028845