{"id":1185,"date":"2009-06-11T10:00:55","date_gmt":"2009-06-11T14:00:55","guid":{"rendered":"http:\/\/onlineappsdba.com\/index.php\/2009\/06\/11\/common-wait-events-in-a-real-application-clusters\/"},"modified":"2009-06-11T11:07:24","modified_gmt":"2009-06-11T15:07:24","slug":"common-wait-events-in-a-real-application-clusters","status":"publish","type":"post","link":"https:\/\/onlineappsdba.com\/index.php\/2009\/06\/11\/common-wait-events-in-a-real-application-clusters\/","title":{"rendered":"Common Wait Events in a Real Application Clusters"},"content":{"rendered":"<p><strong>Difference in single instance and RAC instance:<\/strong><\/p>\n<p>In a single database instance environment, there will be only one set of shared memory segments for the database. In other words, the buffer cache and shared pool are local to that particular instance; at any point in time the processes attached to that particular instance will be accessing only one set of memory structures.<\/p>\n<p>However, in the RAC environment, multiple instances share the same database. The buffer cache is split among these multiple instances; each instance has its own buffer cache and other well-known SGA structures. It is possible for a buffer to be in the buffer cache of one of the instances on another node. The remote instance\u2019s Lock Manager Service (LMS) processes will be accessing the global buffer cache, and the DBWR process will be accessing the local buffer cache.<\/p>\n<p><strong><u>Global Buffer Cache in Real Application Clusters<\/u><\/strong><\/p>\n<p>The data buffer cache is shared by more than one instance, and the buffer cache is called the global cache. Each instance has its own buffer cache local to that particular instance, and all of the buffer caches together create the global cache.<\/p>\n<p>Global Cache waits:<\/p>\n<p>The most common wait events in the RAC environment related to the global cache are:<\/p>\n<p>1. Global cache cr request<\/p>\n<p>2. Global cache busy<\/p>\n<p><strong><u>1. Global Cache cr Request:<\/u><\/strong><\/p>\n<p>When a process requires one or more blocks, Oracle first checks whether it has those (blocks) in its local cache. When a session requests a block(s) that was not found in its local cache, it will request that the resource master grant shared access to those blocks. If the blocks are in the remote cache, then the blocks are transferred using the interconnect to the local cache. The time waited to get the blocks from the remote cache is accounted in the global cache cr request wait event.<\/p>\n<p>Global cache cr request waits are followed by the db file sequential\/scattered read waits. Excessive waits for global cache cr request may be an indication of a slow interconnects.<\/p>\n<p>You can use the oradebug ipc command to verify if the private network is used for cache transfer between instances.<\/p>\n<p>SQL&gt; oradebug setmypid<\/p>\n<p>Statement processed.<\/p>\n<p>SQL&gt; oradebug ipc<\/p>\n<p>Information written to trace file.<\/p>\n<p>SQL&gt; oradebug tracefile_name<\/p>\n<p>\/apps\/oracle\/asm\/product\/10.2.0\/db_1\/admin\/RAC\/udump\/rac1_ora_4749.trc<\/p>\n<p>SQL&gt; host<\/p>\n<p>[oracle@rac1 bin]$ cat \/apps\/oracle\/asm\/product\/10.2.0\/db_1\/admin\/RAC\/udump\/rac1<\/p>\n<p>_ora_4749.trc\u00a0 (trace file content the detail of the IPC configuration)<\/p>\n<p>admno 0x2b360ab admport:<\/p>\n<p>SSKGXPT 0xcc1df2c flags SSKGXPT_READPENDING\u00a0\u00a0\u00a0\u00a0 info for network 0<\/p>\n<p>socket no 7\u00a0\u00a0\u00a0\u00a0 <u>IP 192.168.1.134 <\/u>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0UDP 27278<\/p>\n<p>sflags SSKGXPT_UP<\/p>\n<p>info for network 1<\/p>\n<p>socket no 0\u00a0\u00a0\u00a0\u00a0 IP 0.0.0.0\u00a0\u00a0\u00a0\u00a0\u00a0 UDP 0<\/p>\n<p>sflags SSKGXPT_DOWN<\/p>\n<p>active 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 actcnt 1<\/p>\n<p>context timestamp 0<\/p>\n<p>From the trace file, it is clear that the private network 192.168.1.134 is used for the cache fusion traffic and the protocol used is UDP.<\/p>\n<p><strong><u>Global Cache Statistics <\/u><\/strong><\/p>\n<p>The statistics related to global cache are available from the V$SYSSTAT view.<\/p>\n<p>SQL&gt; select name,value<\/p>\n<p>2\u00a0 from v$sysstat<\/p>\n<p>3\u00a0 where name like &#8216;gc%&#8217;;<\/p>\n<p align=\"left\">NAME\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 VALUE<\/p>\n<p align=\"left\">&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212; &#8212;&#8212;&#8212;-<\/p>\n<p align=\"left\">gcs messages sent\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 7064<\/p>\n<p align=\"left\">gc cr blocks served\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 198<\/p>\n<p align=\"left\">gc cr block build time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2<\/p>\n<p align=\"left\">gc cr block flush time\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 38<\/p>\n<p align=\"left\">gc cr block send time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 17<\/p>\n<p align=\"left\">gc current blocks served\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 3509<\/p>\n<p align=\"left\">gc current block pin time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 10<\/p>\n<p align=\"left\">gc current block flush time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 7<\/p>\n<p align=\"left\">gc current block send time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 174<\/p>\n<p align=\"left\">gc cr blocks received\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 178<\/p>\n<p align=\"left\">gc cr block receive time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 357<\/p>\n<p align=\"left\">gc current blocks received\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 118<\/p>\n<p align=\"left\">gc current block receive time\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 195<\/p>\n<p align=\"left\">gc blocks lost\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0 0<\/p>\n<p align=\"left\">gc claim blocks lost\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0<\/p>\n<p align=\"left\">gc blocks corrupt\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0<\/p>\n<p align=\"left\">gc CPU used by this session\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2223<\/p>\n<p>17 rows selected.<\/p>\n<p><strong><u>2. Global Cache Busy <\/u><\/strong><\/p>\n<p>In a cluster environment, each instance might be mastering its own set of data. Depending on the state of that buffer in the remote instance, the pin times may increase proportionally with the time it takes to service the block request.<\/p>\n<p>If the buffer is busy at the cache level, you can use the following SQL to get the operations that are keeping the buffer busy.<\/p>\n<p>SQL&gt; select a.kcbwhdes &#8220;module&#8221;,<br \/>\n2\u00a0\u00a0 b.why0 &#8220;calls&#8221;,<br \/>\n3\u00a0\u00a0 b.why2 &#8220;waits&#8221;,<br \/>\n4\u00a0 b.other_wait &#8220;caused waits&#8221;<br \/>\n5\u00a0 from\u00a0 x$kcbwh a,x$kcbsw b<br \/>\n6\u00a0\u00a0 where a.indx = b.indx<br \/>\n7\u00a0 and b.other_wait &gt; 0<br \/>\n8\u00a0 order by b.other_wait;<\/p>\n<p>module\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 calls\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 waits\u00a0\u00a0\u00a0\u00a0\u00a0 caused_waits<br \/>\n&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;- &#8212;-<br \/>\nkdswh02: kdsgrp\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 53440\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2<\/p>\n<p>kdswh01: kdstgr\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 4402\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2<\/p>\n<p><u>Common Operations Causing buffer busy waits<\/u><u> <\/u><\/p>\n<p>Module: Definition<\/p>\n<p>Kdsgrp: Performs get row piece. Typically, row pieces are affected only in case of chained and migrated rows. Row chaining has to be analyzed and fixed.<\/p>\n<p>Kdstgr: Performs full table scan get row. Rows are accessed by a full table scan. Check the number of FULL table scans<\/p>\n<p>Kdiixs: Perform index range scan<\/p>\n<p><u><\/u><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Difference in single instance and RAC instance: In a single database instance environment, there will be only one set of [&hellip;]<\/p>\n","protected":false},"author":115,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center 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