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诊断并解决ORA-04031 错误

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Jun 07, 2016 pm 05:17 PM

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诊断并解决ORA-04031 错误，当我们在共享池中试图分配大片的连续内存失败的时候，Oracle首先清除池中当前没使用的所有对象，使空

诊断并解决ORA-04031 错误

当我们在共享池中试图分配大片的连续内存失败的时候，Oracle首先清除池中当前没使用的所有对象，使空闲内存块合并。如果仍然没有足够大单个的大块内存满足请求,就会产生ORA-04031 错误。

当这个错误出现的时候你得到的错误解释信息类似如下:

04031, 00000, "unable to allocate %s bytes of shared memory (\"%s\",\"%s\",\"%s\",\"%s\")" // *Cause: More shared memory is needed than was allocated in the shared // pool. // *Action: If the shared pool is out of memory, either use the // dbms_shared_pool package to pin large packages, // reduce your use of shared memory, or increase the amount of // available shared memory by increasing the value of the // INIT.ORA parameters "shared_pool_reserved_size" and // "shared_pool_size". // If the large pool is out of memory, increase the INIT.ORA // parameter "large_pool_size". 1.共享池相关的实例参数

在继续之前，有必要理解下面的实例参数:

SHARED_POOL_SIZE
这个参数指定了共享池的大小，单位是字节。可以接受数字值或者数字后面跟上后缀"K" 或 "M" 。"K"代表千字节, "M"代表兆字节。

SHARED_POOL_RESERVED_SIZE
指定了为共享池内存保留的用于大的连续请求的共享池空间。当共享池碎片强制使 Oracle 查找并释放大块未使用的池来满足当前的请求的时候，这个参数和SHARED_POOL_RESERVED_MIN_ALLOC 参数一起可以用来避免性能下降。

这个参数理想的值应该大到足以满足任何对保留列表中内存的请求扫描而无需从共享池中刷新对象。既然操作系统内存可以限制共享池的大小，一般来说，你应该设定这个参数为 SHARED_POOL_SIZE 参数的 10% 大小。

SHARED_POOL_RESERVED_MIN_ALLOC 这个参数的值控制保留内存的分配。如果一个足够尺寸的大块内存在共享池空闲列表中没能找到，内存就从保留列表中分配一块比这个值大的空间。默认的值对于大多数系统来说都足够了。如果你加大这个值，那么Oracle 服务器将允许从这个保留列表中更少的分配并且将从共享池列表中请求更多的内存。这个参数在Oracle 8i 和更高的版本中是隐藏的。提交如下的语句查找这个参数值: SELECT nam.ksppinm NAME, val.ksppstvl VALUE FROM x$ksppi nam, x$ksppsv val WHERE nam.indx = val.indx AND nam.ksppinm LIKE '%shared%' ORDER BY 1; 10g 注释：Oracle 10g 的一个新特性叫做 "自动内存管理" 允许DBA保留一个共享内存池来分shared pool,buffer cache, java pool 和large pool。一般来说，当数据库需要分配一个大的对象到共享池中并且不能找到连续的可用空间，，将自动使用其他SGA结构的空闲空间来增加共享池的大小。既然空间分配是Oracle自动管理的，ora-4031出错的可能性将大大降低。自动内存管理在初始化参数SGA_TARGET大于0的时候被激活。当前设定可以通过查询v$sga_dynamic_components 视图获得。请参考10g管理手册以得到更多内容。

2.诊断ORA-04031 错误

注：大多数的常见的 ORA-4031 的产生都和 SHARED POOL SIZE 有关，这篇文章中的诊断步骤大多都是关于共享池的。　对于其它方面如Large_pool或是Java_pool，内存分配算法都是相似的，一般来说都是因为结构不够大造成。

ORA-04031 可能是因为 SHARED POOL 不够大，或是因为碎片问题导致数据库不能找到足够大的内存块。

ORA-04031 错误通常是因为库高速缓冲中或共享池保留空间中的碎片。在加大共享池大小的时候考虑调整应用,使用共享的SQL 并且调整如下的参数： SHARED_POOL_SIZE, SHARED_POOL_RESERVED_SIZE, SHARED_POOL_RESERVED_MIN_ALLOC. 首先判定是否ORA-04031 错误是由共享池保留空间中的库高速缓冲的碎片产生的。提交下的查询： SELECT free_space, avg_free_size,used_space, avg_used_size, request_failures, last_failure_size FROM v$shared_pool_reserved; 如果: REQUEST_FAILURES > 0 并且 LAST_FAILURE_SIZE > SHARED_POOL_RESERVED_MIN_ALLOC

那么ORA-04031 错误就是因为共享池保留空间缺少连续空间所致。要解决这个问题,可以考虑加大SHARED_POOL_RESERVED_MIN_ALLOC 来降低缓冲进共享池保留空间的对象数目，并增大 SHARED_POOL_RESERVED_SIZE 和 SHARED_POOL_SIZE 来加大共享池保留空间的可用内存。

如果： REQUEST_FAILURES > 0 并且 LAST_FAILURE_SIZE 那么是因为在库高速缓冲缺少连续空间导致ORA-04031 错误。

第一步应该考虑降低SHARED_POOL_RESERVED_MIN_ALLOC 以放入更多的对象到共享池保留空间中并且加大SHARED_POOL_SIZE。

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