ORA-4031錯誤 解決方案，ora-4031解決方案
遇到ORA-4031錯誤時，你的心裡會不會發怵？ORA-4031很容易導致資料庫出現異常崩潰，當Oracle的核心進程無法獲得共用池記憶體時，它們會把資料庫異常宕掉。當然，ORA-4031就像黃燈一樣，它在提醒你需要馬上採取緊急策略了。不是說它一出現，資料庫馬上就會宕機。
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，也就是說共用池記憶體不足的情況下，我們該如何釋放記憶體呢？你有木有遇到過相應的情形呢？請回憶下當時是如何解決的？
3.有一句俗語叫丟車保帥，執行計畫是SQL核心關鍵所在，是否意味著在釋放記憶體時，不應該覆蓋執行計畫這部分？當執行計畫部分佔用記憶體比較多時，如何最佳化呢？
4.消耗共用池記憶體的主要有兩種對象，一種是SQL，而是預存程序、函數、包等這類可執行對象，當遇到4031錯誤時，您覺得需要優先釋放哪種對象
問題分析:
1、ORA-4031錯誤的原因，一般是大量的hard parse導致了shared pool中的free list中產生大量的記憶體小片段，當一個需要很大記憶體來進行hard parse的sql語句到來時，無法從free list中找到記憶體，即使進行記憶體的釋放，還是不能找到符合的記憶體塊。從而報ORA-4031錯誤。
2. ORA-4031錯誤的解決方案：
1）alter system flush shared_pool;將shared pool中的所有記憶體清空。該方法治標不治本。2）共用SQL語句：規範SQL語句的書寫；使用綁定變數；找到沒有使用綁定變數的SQL： 如果在結果中發現一系列僅僅字面值不同的SQL，則可以修改cursor_sharing參數： alter system set cursor_sharing = 'force'; 來強制使用綁定變數。3）使用shared pool中的保留區： select request_misses from v$shared_pool_reserved; 如果結果大於0，則可以調大shared_pool_reserved的大小；SQL> show parameter shared_poolNAME TYPE VALUE------------------------------------ ----------- ------------------------------shared_pool_reserved_size big integer 4Mshared_pool_size big integer 0alter system set shared_pool_reserved=xxM scope=both;4）使用dbms_shared_pool.keep('對象名')將使用記憶體很大的對象keep在記憶體中： 先要執行：@?/rdbms/admin/dbmspool.sqlSQL> @?/rdbms/admin/dbmspool.sqlPackage created.Grant succeeded.View created.Package body created.
再查出需要keep的對象：SQL> select owner,name,namespace,type,sharable_mem from v$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 33215SYSMAN EMD_COLLECTION BODY PACKAGE BODY 33233SYS DBMS_SHARED_POOL BODY PACKAGE BODY 12644SYS SYS$RAWTOANY TABLE/PROCEDURE FUNCTION 12640SYSMAN EMD_MAINTENANCE TABLE/PROCEDURE PACKAGE 29030SYSMAN EMD_MAINTENANCE BODY PACKAGE BODY 62930SYSMAN MGMT_JOB_ENGINE BODY PACKAGE BODY 218914SYSMAN EM_PING BODY PACKAGE BODY 29086SYS DBMS_BACKUP_RESTORE BODY PACKAGE BODY 95519SYSMAN EMD_LOADER TABLE/PROCEDURE PACKAGE 12641SYSMAN EMD_LOADER BODY PACKAGE BODY 71861SYS PRVT_HDM BODY PACKAGE BODY 43624SYSMAN MGMT_JOB_ENGINE TABLE/PROCEDURE PACKAGE 24938SYS STANDARD BODY PACKAGE BODY 24960SYSMAN EM_SEVERITY_REPOS BODY PACKAGE BODY 33236SYS PRVT_ADVISOR TABLE/PROCEDURE PACKAGE 12640SYSMAN MGMT_GLOBAL TABLE/PROCEDURE PACKAGE 29902SYS DBMS_STANDARD TABLE/PROCEDURE PACKAGE 24929SYS DBMS_ADVISOR BODY PACKAGE BODY 25000SYS PRVT_HDM TABLE/PROCEDURE PACKAGE 16732SYS PRVT_ADVISOR BODY PACKAGE BODY 66780SYS DBMS_RCVMAN TABLE/PROCEDURE PACKAGE 43295SYS STANDARD TABLE/PROCEDURE PACKAGE 438648SYS DBMS_RCVMAN BODY PACKAGE BODY 375759
24 rows selected.5）增加shared_pool_size的大小：SQL> select component,current_size from v$sga_dynamic_components;
COMPONENT CURRENT_SIZE---------------------------------------------------------------- ------------shared pool 75497472large pool 4194304java pool 4194304streams pool 0DEFAULT buffer cache 130023424KEEP buffer cache 0RECYCLE buffer cache 0DEFAULT 2K buffer cache 0DEFAULT 4K buffer cache 0DEFAULT 8K buffer cache 0DEFAULT 16K buffer cache 0DEFAULT 32K buffer cache 0ASM Buffer Cache 0
13 rows selected.
sga_max_size：SGA允許的最大值，修改必須重啟；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$SHARED_POOL_ADVICE來設定shared pool的大小
V$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 |
可以使用下面的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<0then 0 else current_parse_time_elapsed_s + adjustment_s end response_timefrom (select shared_pool_size_for_estimate,shared_pool_size_factor,estd_lc_time_saved_factor,a.estd_lc_time_saved,e.value/100current_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 294.37Shared Pool 72 1 257.37Shared Pool 80 1.0009 226.37Shared Pool 88 1.0016 201.37Shared Pool 96 1.0022 181.37Shared Pool 104 1.0027 166.37Shared Pool 112 1.0029 156.37Shared Pool 120 1.0032 149.37Shared Pool 128 1.0033 144.37Shared Pool 136 1.0034 141.37Shared Pool 144 1.0034 139.37
11 rows selected.
