共计 1714 个字符,预计需要花费 5 分钟才能阅读完成。
在发送给客户端。与之相干的另一个参数就是 SDU(session data unit),预抓取在 PGA 所占的内存大小和 SDU 大小相干,默认是 8K.
SQL> show arraysize
arraysize 15
SQL> create table jason as select * from dba_objects;
Table created.
SQL>
SQL>
SQL> select count(1) from dba_objects;
COUNT(1)
———-
50042
SQL>
SQL>
SQL> set autot trace
SQL>
SQL>
SQL>
SQL> select * from jason;
50042 rows selected.
Execution Plan
———————————————————-
Plan hash value: 1258222954
—————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
—————————————————————————
| 0 | SELECT STATEMENT | | 44426 | 7679K| 155 (2)| 00:00:02 |
| 1 | TABLE ACCESS FULL| JASON | 44426 | 7679K| 155 (2)| 00:00:02 |
—————————————————————————
Note
—–
– dynamic sampling used for this statement
Statistics
———————————————————-
0 recursive calls
0 db block gets
3992 consistent gets
0 physical reads
0 redo size
2544199 bytes sent via SQLwww.pizei.com*Net to client
37188 bytes received via SQL*Net from client
3338 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
50042 rows processed
SQL> set arraysize 400
SQL>
SQL>
SQL>
SQL> /
SQL> /
50042 rows selected.
Execution Plan
———————————————————-
Plan hash value: 1258222954
—————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
—————————————————————————
| 0 | SELECT STATEMENT | | 44426 | 7679K| 155 (2)| 00:00:02 |
| 1 | TABLE ACCESS FULL| JASON | 44426 | 7679K| 155 (2)| 00:00:02 |
—————————————————————————
Note
—–
– dynamic sampling used for this statement
Statistics
———————————————————-
0 recursive calls
0 db block gets
817 consistent gets
0 physical reads
0 redo size
1956586 bytes sent via SQL*Net to client
1867 bytes received via SQL*Net from client
127 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
50042 rows processed
能够看到当咱们把 arraysize 从默认的 15 调整到 400 后 consistent gets 逻辑读从原来的 3992 降落到 817,bytes received via SQL*Net from client 相干的页游的值也有显著的降落。
arraysize 参数的设置对大数据的范畴比方全表扫性能进步还是比拟大的,所以在网络带宽容许的状况下适当调大 arraysize 和估算 SDU 的值,对缩小
逻辑读,缩小网络交互性,从而介绍 CPU 的耗费帮忙还是比拟大的。
正文完