SGA include:
1 data structure portion fixed size
Second data block buffer database buffers
3 redo log buffer redo buffers
4 shared pool variable size
Permanent use shared memory: process information data, session information data, special-purpose memory segment
With shared pool fragmentation intensifies: generating error ORA-4031
1 to increase the initial allocation value
Every time a group of extensions 2
Shared pool internal structure:
1 PERMANENT
2 FREEABLE
3 RECERATEABLE
4 FREEABLE WITH MARK
Shared pool fragmentation of the case by monitoring internal view X $ KSMSP
Large shared pool will bring some overhead
Shared pool latch will increase competition
Regular updates shared pool shared pool will help to maintain stable performance
The average waiting time related to the shared pool latch, the number of overtime --- to determine the degree of fragmentation shared pool
Cursor: a parent cursor, multiple sub-cursor
Different users, through the results of a SQL get is different, and therefore can not be shared; different execution plan, nor can share
Reproduced in: https: //my.oschina.net/u/204616/blog/545056