1、产生原因 该等待事件通常发生在数据库多块读时，表示发生了与全表扫描和快速索引扫描相关的等待。通常意味着全表扫描过多，或者I/O 能力不足，或者I/O 竞争。 2、确定产生问题对象方法 a)查找全表扫描的SQL 语句可以使用以下语句： select sql_text from v$sqltext t, v$sql_plan p where t.hash_value = p.hash_value and p.operation = ‘TABLE ACCESS‘ and p.options = ‘FULL‘ order by p.hash_value, t.piece; b)查找Fas...
It can also happen during buffer prefetching, as an optimization (rather than performing multiple single-block reads). Database blocks that need to be changed as part of recovery are read in parallel from the database.Wait Time: Wait until all of the I/Os are completed解释： db file parallel read 这在恢复期间发生。 它也可能在缓冲区预取期间发生，作为优化（而不是执行多个单块读取）。 从数据库并...
. A sequential read is a single-block read.Single block I/Os are usually the result of using indexes. Rarely, full table scan calls could get truncated to a single block call becauseof extent boundaries, or buffers present in the buffer cache. These waits would also show up as db file sequential read.Check the following V$SESSION_WAIT parameter columns:P1: The absolute file numberP2: The block b...
call to return. A db file scattered read issues a scattered read to read thedata into multiple discontinuous memory locations. A scattered read is usually a multiblock read. It can occur for a fast full scan (of an index) in addition to a full table scan.The db file scattered read wait event identifies that a full scan is occurring. When performing a full scan into the buffercache, the blocks re...
Causes： DBWR may not be keeping up with writing dirty buffers in the following situations:The I/O system is slow.There are resources it is waiting for, such as latches.The buffer cache is so small that DBWR spends most of its time cleaning out buffers for server processes.The buffer cache is so big that one DBWR process is not enough to free enough buffers in the cache to satisfy requests.Acti...
Query V$WAITSTAT for the wait statistics for each class of buffer. Common buffer classes that have buffer busy waits include data block, segment header, undo header, and undo block.Check the following V$SESSION_WAIT parameter columns: P1: File IDP2: Block IDP3: Class ID解释： 此等待表示缓冲区高速缓存中存在多个进程尝试同时访问的缓冲区。 查询V$WAITSTAT为每类缓冲区的等待统计信息。 具有缓冲区忙等待...
TypicallyDBWR has to free up some buffers when you want to read something from the disk.During this process there are chances that you will be waiting for your local buffer(i.e blocks dirtied/invalidated by your session) to be written to disk. Duringthis time the waits are shown as local write waits.当你想从此盘读取数据，DBDW不得不清空一些buffer。在此过程中，可能会遇到等待你本地buffer写入磁盘（如脏...
Logical reads: 6,959.90 2,819.08 Block changes: 15.52 6.28 Physical reads: 554.17 224.46 Physical writes: 391.05 158.39 User calls: 80.09 32.44 Parses: 13.3...
“SQL*Net message from client”与“SQL*Net message to client”，两者有点区别，下面整理这方面的资料如下： SQL*Net message from client 表示服务端等待着Cilent发来请求让它处理，这时就会产生SQL*Net message from client等待事件。 而我们把这种Wait叫做空闲事件（ildel event）,并不代表真正的Loading. SQL*Net message to client 这个等待事件发生在服务段向客户端发送...
----------------------------------------------------------------------------- 来自盖大师（eygle）对log file sync等待事件优化的总结，供各位puber们学习参考：http://www.eygle.com/statspack/statspack14-LogFileSync.htm 当一个用户提交(commits)或者回滚(rollback),session的redo信息需要写出到redo logfile中.用户进程将通知LGWR执行写出操作,LGWR完成任务以后会通知用户进程.这个等待事件就是指用户进程等待LGWR的写完...
这是3月份某客户的情况，原因是server硬件故障后进行更换之后，业务翻译偶尔出现提交缓慢的情况。我们先来看下awr的情况。 我们能够看到，该系统的load profile信息事实上并不高，每秒才21个transaction。先来看看top5events： 从top 5event，我们能够发现，log file sync的avg wait很之高，高达124ms。大家应该知道，对于绝大多数情况 下，log file sync的平均等待时间是小于5ms的，这个值有点高的离谱。 我们知道，产生log file...
实验：某个分区数据块损坏，不完全恢复此分区表数据背景：数据库没有有效备份，某个分区中有数据块损坏。要求：最大限度恢复此分区数据。环境：RHEL 6.4 + Oracle 11.2.0.41. 初始化实验环境 2. 模拟分区中有数据块损坏情景 3. 尝试使用Oracle内部事件10231进行不完全恢复 Reference 1. 初始化实验环境 初始化创建模拟实验环境用到的表空间、业务用户、表，并导入测试数据。本次实验用到表空间DBS_D_JINGYU, 业务用户JINGYU, 分区表...
）关闭掉。部分awr截图如下：APPLIES TO:Oracle Database - Enterprise Edition - Version 11.2.0.3 and laterInformation in this document applies to any platform.SYMPTOMSo Grid Infrastructure home and rdbms home is running on 11.2.0.3.7.o Database instance fail to start, with ORA-7445 [strstr()]o The failing process is gen0, and the current Wait Stack shows waiting for ‘CRS call completion‘o The call ...
session set events ‘10046 trace name context forever 12‘ --启用tracealter session set events ‘10046 trace name context off‘ --停止trace 11g之后 alter session set events ‘SQL_TRACE wait=true‘;2.2 方法2 SQL> select sid,serial#,username from v$session where username is not null;SID SERIAL# USERNAME ---------- ---------- -----------------------------------...
通过db time/Elapsed显示数据库的压力并不是很大。 每秒钟产生的redo log 8M，数据库的IO写压力很大。 redo 切换频率1 原因只要是需要读控制文件的操作期间,都调用并持有 CF enqueue, CF 块用于控制文件相关事务的序列化 操作和在控制文件共享部分的读写操作。 一般来说，控制文件的CF enqueue 锁的申请和持有时间是非常短暂的。 数据库的下列操作会调用该锁：checkpointing switching logfiles archiving redologs perfor...