ORA-4031错误 解决方法

遇到ORA-4031错误时。你的心里会不会发怵？ORA-4031非常easy导致数据库出现异常崩溃，当Oracle的核心进程无法获得共享池内存时。它们会把数据库异常宕掉。当然，ORA-4031就像黄灯一样，它在提醒你须要立即採取紧急策略了。不是说它一出现，数据库立即就会宕机。

话题讨论：
1.ORA-4031是Oracle中最令人厌恶的报错，它的出现有哪几种原因？

2.一旦出现4031错误。也就是说共享池内存不足的情况下，我们该怎样释放内存呢？你有木有遇到过对应的情形呢？请回顾下当时是怎样解决的？

3.有一句俗语叫丢车保帅。运行计划是SQL核心关键所在。是否意味着在释放内存时，不应该覆盖运行计划这部分？当运行计划部分占用内存比較多时，怎样优化呢？

4.消耗共享池内存的主要有两种对象，一种是SQL，而是存储过程、函数、包等这类可运行对象。当遇到4031错误时，您认为须要优先释放哪种对象

问题分析:

1、ORA-4031错误的原因，通常是大量的hard parse导致了shared pool中的free list中产生大量的内存小碎片，当一个须要非常大内存来进行hard parse的sql语句到来时。无法从free list中找到内存，即使进行内存的释放。还是不能找到符合的内存块。从而报ORA-4031错误。

2. ORA-4031错误的解决方法：

1）alter system flush shared_pool;将shared pool中的全部内存清空。

该方法治标不治本。

2）共享SQL语句：规范SQL语句的书写。使用绑定变量；找到没有使用绑定变量的SQL：

   假设在结果中发现一系列只字面值不同的SQL，则能够改动cursor_sharing參数：

   alter system set cursor_sharing = 'force'; 来强制使用绑定变量。

3）使用shared pool中的保留区：

   select request_misses from v$shared_pool_reserved;

   假设结果大于0，则能够调大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('对象名')将使用内存非常大的对象keep在内存中：

   先要运行：@?/rdbms/admin/dbmspool.sql

SQL> @?/rdbms/admin/dbmspool.sql

Package created.

Grant succeeded.

View created.

Package body created.

再查出须要keep的对象：

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，改动必须重新启动；

sga_target：必须小于sga_max_size, 表示当前SGA的最大值。

alter system set shared_pool_size=xxM scope=both;

3. 使用V$SHARED_POOL_ADVICE来设置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

能够使用以下的SQL语句来预估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.