频发：故障排除之又见 ORA-4031丨云和恩墨技术通讯
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本期目录：
新闻：2019年11月数据库流行度排行
经验：Oracle RAC跨节点访问数据块，节点长事务加剧gc等待
经验：IBM MQ通道连接数达到最大故障分析
问题：子游标过多导致数据库HANG
频发：再谈Library Cache Lock
频发：故障排除之又见ORA-4031
警示：强制关闭OGG进程触发bug致abended
公告：首届墨天轮年度十大突出贡献人物评选活动
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部分精选-频发：故障排除之又见 ORA-4031 作者：候静远
当遇到ORA-4031错误时，你会不会内心一紧。Oracle进程在向SGA申请内存时，如果申请失败，则会抛出这个错误，大部分情况下是在向SGA中的 shared pool申请内存时失败。严重情况下，可能导致数据库出现异常崩溃。本文分享客户近期碰到的一起由于ORA-4031问题导致数据库异常宕机的案例，供大家参考。
问题描述
2019年9月4日凌晨3点左右，接到监控系统告警：数据库出现异常，无法连接。登陆到数据库1节点查看后台alert日志发现有大量ORA-04031报错，2节点有少量报错。为了尽快恢复业务，尝试直接重启1节点数据库，重启完成之后恢复正常。
问题分析
1. 节点后台对应alert日志：
Wed Sep 04 03:57:50 2019Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx/trace/xxxxx_smon_29747.trc:ORA-00604: error occurred at recursive SQL level 1ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","update sys.col_usage$ set ...","sga heap(2,0)","kglsim object batch")Wed Sep 04 03:58:10 2019Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx/trace/xxxxx_smon_29747.trc:ORA-00604: error occurred at recursive SQL level 1ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","update sys.col_usage$ set ...","sga heap(1,0)","kglsim object batch")Wed Sep 04 03:58:26 2019Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx/trace/xxxxx_smon_29747.trc:ORA-00604: error occurred at recursive SQL level 1ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","update sys.col_usage$ set ...","sga heap(7,0)","kglsim object batch")Wed Sep 04 03:58:42 2019Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx/trace/xxxxx_smon_29747.trc:ORA-00604: error occurred at recursive SQL level 1ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","update sys.col_usage$ set ...","sga heap(6,0)","kglsim object batch")Wed Sep 04 03:58:57 2019Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx/trace/xxxxx_smon_29747.trc:ORA-00604: error occurred at recursive SQL level 1ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","update sys.mon_mods$ set ins...","sga heap(5,0)","kglsim object batch")Wed Sep 04 03:59:08 2019Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx/trace/xxxxx_xxx0_42548.trc:ORA-00604: error occurred at recursive SQL level 1ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select count(*) from sys.job...","sga heap(3,0)","kglsim object batch")Wed Sep 04 03:59:10 2019License high water mark = 97USER (ospid: 28750): terminating the instance统计1节点每个子池及duration出现04031的次数，sga heap(n,0)-n代表第几个子池，0代表是第几个duration：
根据alert日志可以看出，所有的ora-4031都发生在shared pool子池的第0个duration上。
Summary of resize operations history:shared pool start 3.19 GB now 3.19 GB 0 grows 0 shrinkslarge pool start 0.50 GB now 0.50 GB 0 grows 0 shrinksjava pool start 0.50 GB now 0.50 GB 0 grows 0 shrinksSGA Target start 32.00 GB now 32.00 GB 0 grows 0 shrinksDEFAULT buffer cache start 27.59 GB now 27.59 GB 0 grows 0 shrinksPGA Target start 11.00 GB now 11.00 GB 0 grows 0 shrinks发现shared pool并没有进行resize。
==============================================TOP 20 MEMORY USES ACROSS SGA HEAP 1 - 7----------------------------------------------"KGLH0 " 1103 MB 19%"SQLA " 1081 MB 18%"free memory " 835 MB 14%"gcs resources " 794 MB 14%"gcs shadows " 550 MB 9%"db_block_hash_buckets " 178 MB 3%"ASH buffers " 160 MB 3%"KGLHD " 157 MB 3%"Checkpoint queue " 156 MB 3%"kglsim object batch " 90 MB 2%"kglsim heap " 56 MB 1%"ges resource " 53 MB 1%"ges enqueues " 43 MB 1%"KGLDA " 41 MB 1%"dbwriter coalesce buffer " 40 MB 1%"dirty object counts array " 40 MB 1%"object queue " 35 MB 1%"gcs res hash bucket " 32 MB 1%"dbktb: trace buffer " 31 MB 1%"FileOpenBlock " 30 MB 1%TOTALS ---------------------------------------Total free memory 830 MBTotal memory alloc. 5026 MBGrand total 5856 MB==============================================2. 节点后台对应的alert日志：
Wed Sep 04 03:23:18 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q002_35378.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(4,0)","kglsim object batch")Wed Sep 04 03:23:23 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q003_35453.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(1,0)","kglsim object batch")Wed Sep 04 03:23:29 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q004_35725.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(5,0)","kglsim object batch")Wed Sep 04 03:23:34 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q001_35778.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(2,0)","kglsim object batch")Wed Sep 04 03:23:39 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q002_36069.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(6,0)","kglsim object batch")Wed Sep 04 03:23:45 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q003_36151.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(3,0)","kglsim object batch")Wed Sep 04 03:23:50 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q004_36242.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(7,0)","kglsim object batch")Wed Sep 04 03:23:55 2019Emon ping encountered error 12801Errors in file /u01/app/oracle/diag/rdbms/xxxxx/xxxxx2/trace/xxxxx2_q001_36305.trc:ORA-12801: error signaled in parallel query server PZ99, instance dnfwglpt1:xxxxx (1)ORA-04031: unable to allocate 3896 bytes of shared memory ("shared pool","select inst_id, reg_id, num_...","sga heap(4,0)","kglsim object batch")统计2节点每个子池及duration出现04031的次数：
根据alert日志可以看出，所有的ora-4031同样都发生在shared pool子池的第0个duration上，导致4031的根本原因是因为shared pool子池的第0个duration内存不足。
通过设置sga_target的ASMM管理后，共享池(shared_pool)和流池(streams pool)每个子池都是4个duration。它们分别是：instance，session，cursor，execution，只有第四个duration，也就是execution是可以resize的，而当第0个duration内存不足的时候不能resize，就直接会报错ora-4031。
问题解决
通过禁用duration，必须设置参数"_enable_shared_pool_durations=fales"，并重启数据库。
alter system set "_enable_shared_pool_durations"=false scope=spfile;
通过该参数设置后，把它们四个duration都合并到一个池中，不会再出现一个duration的内存被耗尽，而另外一个duration仍具有空闲内存，对于共享池和流池都是这样；设置sga_target之后，所有池都会通过buffer cache来传输granules（颗粒）整数倍大小的内存，如果shrink，则返回buffer cache，没有从一个pool到另外一个pool的直接传输，所有的内存resize都会以buffer cache作为源和目标。
设置该参数的唯一负面影响是SGA resize的时候，不能从shared pool中取内存到其他的pool。
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