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。