話題討論：
1.ORA-4031是Oracle中最令人厭惡的報錯，它的出現有哪幾種原因？
2.一旦出現4031錯誤。也就是說共享池內存不足的情況下，我們該怎樣釋放內存呢？你有木有遇到過對應的情形呢？請回顧下當時是怎樣解決的？
3.有一句俗語叫丟車保帥。運行計划是SQL核心關鍵所在。是否意味着在釋放內存時，不應該覆蓋運行計划這部分？當運行計划部分占用內存比較多時，怎樣優化呢？
4.消耗共享池內存的主要有兩種對象，一種是SQL，而是存儲過程、函數、包等這類可運行對象。當遇到4031錯誤時，您認為須要優先釋放哪種對象
問題分析:
1、ORA-4031錯誤的原因，通常是大量的hard parse導致了shared pool中的free list中產生大量的內存小碎片，當一個須要非常大內存來進行hard parse的sql語句到來時。無法從free list中找到內存，即使進行內存的釋放。還是不能找到符合的內存塊。從而報ORA-4031錯誤。
2. ORA-4031錯誤的解決方法：
1）alter system flush shared_pool;將shared pool中的全部內存清空。
該方法治標不治本。
2）共享SQL語句：規范SQL語句的書寫。使用綁定變量；找到沒有使用綁定變量的SQL：
假設在結果中發現一系列只字面值不同的SQL，則能夠改動cursor_sharing參數：
alter system set cursor_sharing = 'force'; 來強制使用綁定變量。
3）使用shared pool中的保留區：
select request_misses from v$shared_pool_reserved;
假設結果大於0，則能夠調大shared_pool_reserved的大小；
SQL> show parameter shared_pool
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
shared_pool_reserved_size big integer 4M
shared_pool_size big integer 0
alter system set shared_pool_reserved=xxM scope=both;
4）使用
dbms_shared_pool.keep
('對象名')將使用內存非常大的對象keep在內存中：
先要運行：@?/rdbms/admin/dbmspool.sql
SQL> @?/rdbms/admin/dbmspool.sql
Package created.
Grant succeeded.
View created.
Package body created.
再查出須要keep的對象：
SQL> select owner,name,namespace,type,sharable_mem from v$db_object_cache where sharable_mem>10000
2 and (type='PACKAGE' or type='PACKAGE BODY' or type='FUNCTION' or type='PROCEDURE') and kept='NO';
OWNER NAME NAMESPACE TYPE SHARABLE_MEM
---------- ------------------------- ------------------ --------------- ------------
SYS DBMS_BACKUP_RESTORE TABLE/PROCEDURE PACKAGE 33215
SYSMAN EMD_COLLECTION BODY PACKAGE BODY 33233
SYS DBMS_SHARED_POOL BODY PACKAGE BODY 12644
SYS SYS$RAWTOANY TABLE/PROCEDURE FUNCTION 12640
SYSMAN EMD_MAINTENANCE TABLE/PROCEDURE PACKAGE 29030
SYSMAN EMD_MAINTENANCE BODY PACKAGE BODY 62930
SYSMAN MGMT_JOB_ENGINE BODY PACKAGE BODY 218914
SYSMAN EM_PING BODY PACKAGE BODY 29086
SYS DBMS_BACKUP_RESTORE BODY PACKAGE BODY 95519
SYSMAN EMD_LOADER TABLE/PROCEDURE PACKAGE 12641
SYSMAN EMD_LOADER BODY PACKAGE BODY 71861
SYS PRVT_HDM BODY PACKAGE BODY 43624
SYSMAN MGMT_JOB_ENGINE TABLE/PROCEDURE PACKAGE 24938
SYS STANDARD BODY PACKAGE BODY 24960
SYSMAN EM_SEVERITY_REPOS BODY PACKAGE BODY 33236
SYS PRVT_ADVISOR TABLE/PROCEDURE PACKAGE 12640
SYSMAN MGMT_GLOBAL TABLE/PROCEDURE PACKAGE 29902
SYS DBMS_STANDARD TABLE/PROCEDURE PACKAGE 24929
SYS DBMS_ADVISOR BODY PACKAGE BODY 25000
SYS PRVT_HDM TABLE/PROCEDURE PACKAGE 16732
SYS PRVT_ADVISOR BODY PACKAGE BODY 66780
SYS DBMS_RCVMAN TABLE/PROCEDURE PACKAGE 43295
SYS STANDARD TABLE/PROCEDURE PACKAGE 438648
SYS DBMS_RCVMAN BODY PACKAGE BODY 375759
24 rows selected.
5）添加shared_pool_size的大小：
SQL> select component,current_size from v$sga_dynamic_components;
COMPONENT CURRENT_SIZE
---------------------------------------------------------------- ------------
shared pool 75497472
large pool 4194304
java pool 4194304
streams pool 0
DEFAULT buffer cache 130023424
KEEP buffer cache 0
RECYCLE buffer cache 0
DEFAULT 2K buffer cache 0
DEFAULT 4K buffer cache 0
DEFAULT 8K buffer cache 0
DEFAULT 16K buffer cache 0
DEFAULT 32K buffer cache 0
ASM Buffer Cache 0
13 rows selected.
sga_max_size：SGA同意的最大值，改動必須重新啟動；
sga_target：必須小於sga_max_size, 表示當前SGA的最大值。
alter system set shared_pool_size=xxM scope=both;
3. 使用V$SHARED_POOL_ADVICE來設置shared pool的大小
V$SHARED_POOL_ADVICE displays information about estimated parse time in the shared pool for different pool sizes. The sizes range from 10% of the current shared pool size or the amount of pinned library cache memory (whichever is higher) to 200% of the current shared pool size, in equal intervals. The value of the interval depends on the current size of the shared pool.
| Column | Datatype | Description |
|---|---|---|
| SHARED_POOL_SIZE_FOR_ESTIMATE | NUMBER | Shared pool size for the estimate (in megabytes) |
| SHARED_POOL_SIZE_FACTOR | NUMBER | Size factor with respect to the current shared pool size |
| ESTD_LC_SIZE | NUMBER | Estimated memory in use by the library cache (in megabytes) |
| ESTD_LC_MEMORY_OBJECTS | NUMBER | Estimated number of library cache memory objects in the shared pool of the specified size |
| ESTD_LC_TIME_SAVED | NUMBER | Estimated elapsed parse time saved (in seconds), owing to library cache memory objects being found in a shared pool of the specified size. This is the time that would have been spent in reloading the required objects in the shared pool had they been aged out due to insufficient amount of available free memory. |
| ESTD_LC_TIME_SAVED_FACTOR | NUMBER | Estimated parse time saved factor with respect to the current shared pool size |
| ESTD_LC_LOAD_TIME | NUMBER | Estimated elapsed time (in seconds) for parsing in a shared pool of the specified size |
| ESTD_LC_LOAD_TIME_FACTOR | NUMBER | Estimated load time factor with respect to the current shared pool size |
| ESTD_LC_MEMORY_OBJECT_HITS | NUMBER | Estimated number of times a library cache memory object was found in a shared pool of the specified size |
能夠使用以下的SQL語句來預估shared pool的大小：
select 'Shared Pool' component,shared_pool_size_for_estimate estd_sp_size,estd_lc_time_saved_factor parse_time_factor,case when current_parse_time_elapsed_s + adjustment_s<0
then 0 else current_parse_time_elapsed_s + adjustment_s end response_time
from (
select shared_pool_size_for_estimate,shared_pool_size_factor,estd_lc_time_saved_factor,a.estd_lc_time_saved,e.value/100
current_parse_time_elapsed_s,c.estd_lc_time_saved - a.estd_lc_time_saved adjustment_s from v$shared_pool_advice a,
(select * from v$sysstat where name='parse time elapsed') e,
(select estd_lc_time_saved from v$shared_pool_advice where shared_pool_size_factor=1) c
);
COMPONENT ESTD_SP_SIZE PARSE_TIME_FACTOR RESPONSE_TIME
-------------- ----------------- ------------------------- -------------
Shared Pool 64 .9989 294.37
Shared Pool 72 1 257.37
Shared Pool 80 1.0009 226.37
Shared Pool 88 1.0016 201.37
Shared Pool 96 1.0022 181.37
Shared Pool 104 1.0027 166.37
Shared Pool 112 1.0029 156.37
Shared Pool 120 1.0032 149.37
Shared Pool 128 1.0033 144.37
Shared Pool 136 1.0034 141.37
Shared Pool 144 1.0034 139.37
11 rows selected.