{"id":695,"date":"2012-03-27T23:54:50","date_gmt":"2012-03-27T15:54:50","guid":{"rendered":"https:\/\/yangtingkun.net\/?p=695"},"modified":"2018-07-10T00:16:30","modified_gmt":"2018-07-09T16:16:30","slug":"%e6%b6%88%e9%99%a411-2%e4%b8%8a%e7%9a%84db-file-parallel-read","status":"publish","type":"post","link":"https:\/\/yangtingkun.net\/?p=695","title":{"rendered":"\u6d88\u966411.2\u4e0a\u7684db file parallel read"},"content":{"rendered":"<p>\u5ba2\u6237\u572811.2.0.3\u73af\u5883\u4e2d\u8fdb\u884c\u538b\u529b\u6d4b\u8bd5\uff0c\u53d1\u73b0\u51fa\u73b0\u5927\u91cf\u7684db file parallel read\u7b49\u5f85\u4e8b\u4ef6\u3002<br \/>\n\u8fd9\u4e2a\u7b49\u5f85\u662f11g\u4ee5\u540e\u624d\u51fa\u73b0\u7684\uff0c\u800c\u572811g\u4ee5\u524d\uff0c\u4e00\u822c\u8fd9\u4e2a\u7b49\u5f85\u4e8b\u4ef6\u53d1\u751f\u5728\u6570\u636e\u6587\u4ef6\u7684\u6062\u590d\u8fc7\u7a0b\u4e2d\u3002\u800c11g\u65b0\u589e\u4e86prefetch\u7684\u7279\u6027\uff0c\u4e5f\u53ef\u80fd\u5bfc\u81f4\u8fd9\u4e2a\u7b49\u5f85\u4e8b\u4ef6\u7684\u4ea7\u751f\u3002<br \/>\n\u5f53\u8fd0\u884c\u538b\u529b\u6d4b\u8bd5\u65f6\uff0c\u540e\u53f0\u7684\u7b49\u5f85\u4e8b\u4ef6\u5982\u4e0b\uff1a<\/p>\n<pre lang=\"SQL\">SQL&gt; select event, count(*) from v$session where username = user group by event order by 2;\r\nEVENT                                                              COUNT(*)\r\n---------------------------------------------------------------- ----------\r\nSQL*Net message from client                                               1\r\nSQL*Net message to client                                                 1\r\ndb file sequential read                                                  24\r\ndb file scattered read                                                   33\r\ndb file parallel read                                                    42<\/pre>\n<p>\u53ef\u4ee5\u770b\u5230\u7528\u6237\u8fdb\u7a0b\u7ecf\u5386\u6bd4\u8f83\u4e25\u91cd\u7684IO\u7b49\u5f85\uff0c\u800c\u6b64\u65f6\u7684db file parallel read\uff0c\u5e76\u4e0d\u4f1a\u5e26\u6765\u6027\u80fd\u63d0\u5347\u3002<br \/>\n\u53ef\u4ee5\u901a\u8fc7\u6dfb\u52a0\u9690\u542b\u53c2\u6570\u7684\u65b9\u6cd5\u6765\u5c4f\u853dprefetch\u529f\u80fd\uff0c\u4ece\u800c\u907f\u514ddb file parallel read\u7b49\u5f85\u4e8b\u4ef6\u7684\u4ea7\u751f\uff1a<\/p>\n<pre lang=\"SQL\">_db_block_prefetch_limit=0\r\n_db_block_prefetch_quota=0\r\n_db_file_noncontig_mblock_read_count=0<\/pre>\n<p>\u53c2\u6570\u6587\u4ef6\u6dfb\u52a0\u8fd9\u4e09\u4e2a\u9690\u542b\u53c2\u6570\u540e\uff0c\u91cd\u542f\u6570\u636e\u5e93\uff0c\u518d\u6b21\u8fd0\u884c\u538b\u529b\u6d4b\u8bd5\uff0c\u53d1\u73b0db file parallel read\u7b49\u5f85\u4e8b\u4ef6\u5df2\u7ecf\u6d88\u5931\uff1a<\/p>\n<pre lang=\"SQL\">SQL&gt; select event, count(*) from v$session where username = user group by event order by 2;\r\nEVENT                                                              COUNT(*)\r\n---------------------------------------------------------------- ----------\r\nSQL*Net message to client                                                 1\r\ndb file scattered read                                                   30\r\ndb file sequential read                                                  70<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u5ba2\u6237\u572811.2.0.3\u73af\u5883\u4e2d\u8fdb\u884c\u538b\u529b\u6d4b\u8bd5\uff0c\u53d1\u73b0\u51fa\u73b0\u5927\u91cf\u7684db file parallel read\u7b49\u5f85\u4e8b\u4ef6\u3002 \u8fd9\u4e2a\u7b49\u5f85\u662f11g\u4ee5\u540e\u624d\u51fa\u73b0\u7684\uff0c\u800c\u572811g\u4ee5\u524d\uff0c\u4e00\u822c\u8fd9\u4e2a\u7b49\u5f85\u4e8b\u4ef6\u53d1\u751f\u5728\u6570\u636e\u6587\u4ef6\u7684\u6062\u590d\u8fc7\u7a0b\u4e2d\u3002\u800c11g\u65b0\u589e\u4e86prefetch\u7684\u7279\u6027\uff0c\u4e5f\u53ef\u80fd\u5bfc\u81f4\u8fd9\u4e2a\u7b49\u5f85\u4e8b\u4ef6\u7684\u4ea7\u751f\u3002 \u5f53\u8fd0\u884c\u538b\u529b\u6d4b\u8bd5\u65f6\uff0c\u540e\u53f0\u7684\u7b49\u5f85\u4e8b\u4ef6\u5982\u4e0b\uff1a SQL&gt; select event, count(*) from v$session where username = user group by event order by 2; EVENT COUNT(*) &#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;&#8212;- &#8212;&#8212;&#8212;- SQL*Net message from client 1 SQL*Net message to client 1 db file sequential read &hellip; <a href=\"https:\/\/yangtingkun.net\/?p=695\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[3],"tags":[576,195,574,575,577,573],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2yiY3-bd","_links":{"self":[{"href":"https:\/\/yangtingkun.net\/index.php?rest_route=\/wp\/v2\/posts\/695"}],"collection":[{"href":"https:\/\/yangtingkun.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/yangtingkun.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/yangtingkun.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/yangtingkun.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=695"}],"version-history":[{"count":2,"href":"https:\/\/yangtingkun.net\/index.php?rest_route=\/wp\/v2\/posts\/695\/revisions"}],"predecessor-version":[{"id":1511,"href":"https:\/\/yangtingkun.net\/index.php?rest_route=\/wp\/v2\/posts\/695\/revisions\/1511"}],"wp:attachment":[{"href":"https:\/\/yangtingkun.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=695"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/yangtingkun.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=695"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/yangtingkun.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=695"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}