很早之前，在一次講課了，用了命令ipcs,發現oracle的共享內段好小，如下：

oracle@mydb?~]$?ipcs?-a------?Shared?Memory?Segments?-------- key????????shmid??????owner??????perms??????bytes??????nattch?????status?????? 0x00000000?32768??????root??????644????????72?????????2??????????????????????? 0x00000000?65537??????root??????644????????16384??????2??????????????????????? 0x00000000?98306??????root??????644????????280????????2??????????????????????? 0x00000000?1409028????oracle????640????????4096???????0??????????????????????? 0x00000000?1441797????oracle????640????????4096???????0??????????????????????? 0x079918e8?1474566????oracle????640????????4096???????0???????????????????????------?Semaphore?Arrays?-------- key????????semid??????owner??????perms??????nsems????? 0x87a36da4?1343489????oracle????640????????154???????------?Message?Queues?-------- key????????msqid??????owner??????perms??????used-bytes???messages

?今天突然想起，剛好有空，來總結一下：

上面顯示Oracle共享內存段只有4096個字節，這太小了吧，哦，對了，我這是Oracle11g：

sys@OCM>?select?*?from?v$version;BANNER -------------------------------------------------------------------------------- Oracle?Database?11g?Enterprise?Edition?Release?11.2.0.3.0?-?64bit?Production PL/SQL?Release?11.2.0.3.0?-?Production CORE????11.2.0.3.0??????Production TNS?for?Linux:?Version?11.2.0.3.0?-?Production NLSRTL?Version?11.2.0.3.0?-?Production

Oraccle11g的對內存的管理用了兩個新的參數：

sys@OCM>?show?parameter?memoryNAME?????????????????????????????????TYPE????????VALUE ------------------------------------?-----------?------------------------------ hi_shared_memory_address?????????????integer?????0 memory_max_target????????????????????big?integer?1G memory_target????????????????????????big?integer?0 shared_memory_address????????????????integer?????0

會不會是參數memory_max_target在作怪呢，把它關了試試，我這里把它設為0，然后重啟數據庫。

sys@OCM>?alter?system?set?memory_max_target=0?scope=spfile;System?altered.sys@OCM>?startup?force; ORACLE?instance?started.Total?System?Global?Area??943669248?bytes Fixed?Size??????????????????2234000?bytes Variable?Size?????????????541067632?bytes Database?Buffers??????????394264576?bytes Redo?Buffers????????????????6103040?bytes Database?mounted. Database?opened.

再看共享內存：

[oracle@mydb?~]$?ipcs?-a------?Shared?Memory?Segments?-------- key????????shmid??????owner??????perms??????bytes??????nattch?????status?????? 0x00000000?32768??????root??????644????????72?????????2??????????????????????? 0x00000000?65537??????root??????644????????16384??????2??????????????????????? 0x00000000?98306??????root??????644????????280????????2??????????????????????? 0x00000000?1802244????oracle????640????????4096???????0??????????????????????? 0x00000000?1835013????oracle????640????????4096???????0??????????????????????? 0x079918e8?1867782????oracle????640????????4096???????0???????????????????????------?Semaphore?Arrays?-------- key????????semid??????owner??????perms??????nsems????? 0x87a36da4?1736705????oracle????640????????154???????------?Message?Queues?-------- key????????msqid??????owner??????perms??????used-bytes???messages

怎么回事，沒變啊？

是不是參數沒改對，繼續校驗參數：

sys@OCM>?show?parameter?memNAME?????????????????????????????????TYPE????????VALUE ------------------------------------?-----------?------------------------------ hi_shared_memory_address?????????????integer?????0 memory_max_target????????????????????big?integer?904M memory_target????????????????????????big?integer?0 shared_memory_address????????????????integer?????0

果然沒改過來，是不是命令alter system set memory_max_target=0 scope=spfile;沒用啊，不能怎么設，但這命令本身設置重啟也沒報錯。

來個狠一點的命令重置默認值：

sys@OCM>?alter?system?reset?memory_max_target;System?altered.sys@OCM>?startup?force; ORACLE?instance?started.Total?System?Global?Area??680665088?bytes Fixed?Size??????????????????2231352?bytes Variable?Size?????????????276825032?bytes Database?Buffers??????????394264576?bytes Redo?Buffers????????????????7344128?bytes Database?mounted. Database?opened. sys@OCM>?show?parameter?memNAME?????????????????????????????????TYPE????????VALUE ------------------------------------?-----------?------------------------------ hi_shared_memory_address?????????????integer?????0 memory_max_target????????????????????big?integer?0 memory_target????????????????????????big?integer?0 shared_memory_address????????????????integer?????0

這下可以了，參數memory_max_target終于等于0了。

我們再來看ORACLE共享內存：

[oracle@mydb?~]$?ipcs?-a------?Shared?Memory?Segments?-------- key????????shmid??????owner??????perms??????bytes??????nattch?????status?????? 0x00000000?32768??????root??????644????????72?????????2??????????????????????? 0x00000000?65537??????root??????644????????16384??????2??????????????????????? 0x00000000?98306??????root??????644????????280????????2??????????????????????? 0x00000000?1933316????oracle????640????????12582912???30?????????????????????? 0x00000000?1966085????oracle????640????????671088640??30?????????????????????? 0x079918e8?1998854????oracle????640????????2097152????30??????????????????????------?Semaphore?Arrays?-------- key????????semid??????owner??????perms??????nsems????? 0x87a36da4?1867777????oracle????640????????154???????------?Message?Queues?-------- key????????msqid??????owner??????perms??????used-bytes???messages

可以了！已從4096字節變成671088640多字節了。，總結只要把參數memory_max_target設為0就能看到。這里不建議大家去這樣改，只是為了解釋一下這個現象。

上面那幅圖留給童鞋們思考，不再解釋了。。。

轉載于:https://blog.51cto.com/guoyjoe/1431363

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