Oracle - 随笔分类 - FangwenYu

About - CONNECT_BY_FILTERING

摘要：About Oracle Hint - CONNECT_BY_FILTERING 阅读全文

posted @ 2013-11-19 21:09 FangwenYu 阅读(1169) 评论(0) 推荐(0)

"DISTINCT" make huge difference

摘要：DISTINCT 可能造成执行计划很大的改变。阅读全文

posted @ 2013-11-14 18:35 FangwenYu 阅读(377) 评论(0) 推荐(0)

Is "UNION ALL" Always Better Than "UNION"? Watch Out!

摘要：UNION or UNION ALL? 阅读全文

posted @ 2013-10-26 21:39 FangwenYu 阅读(561) 评论(0) 推荐(0)

了不起的 “filter(NULL IS NOT NULL)”

摘要：经常会在执行计划中看到很奇怪的"FILTER"操作，然后看对应的执行信息是"filter(NULL IS NOT NULL)". 其实这是优化器非常聪明的“短路”操作。比如下面的这个执行计划，（尤其是从统计信息中可以看到logical/physical reads都是0)(注：在Ask Tom: On Constraints, Metadata, and Truth (http://www.oracle.com/technetwork/issue-archive/2011/11-mar/o21asktom-312223.html) 有提到)Executi 阅读全文

posted @ 2013-09-06 16:41 FangwenYu 阅读(2822) 评论(0) 推荐(0)

对上一篇的补充

摘要：在 “http://www.cnblogs.com/fangwenyu/p/3260907.html” 中提到通过打了一个数据库的补丁来解决"row cache objects"的问题。但是结果很不幸，问题并没有解决！后来通过仔细观察，发现压力测试中随着 vuser的数量增加，DB服务器的usage一直在上升，但是一旦达到或接近100%的时候，发现这个时候就会出现row cache objects 的争用问题了。后来还是老老实实对有问题的SQL进行优化（虽然有些已经很难改动了），然后对一些sequence的cache size进行增加(这个在有个report中反映明显，因为阅读全文

posted @ 2013-09-06 13:52 FangwenYu 阅读(166) 评论(0) 推荐(0)

Latch: Row Cache Objects (One bug?)

摘要：About one Oracle wait event ~ latch:row cache objects. 阅读全文

posted @ 2013-08-15 21:28 FangwenYu 阅读(2275) 评论(0) 推荐(0)

Disable Oracle Automatic Jobs

摘要：By default, Oracle will run some maintance jobs every night. If you don't want to run those jobs, you can just disable them.Query the automatic jobs using the SQL statement below,select * from DBA_AUTOTASK_CLIENTYou would normally see the following 3 jobs:(1)auto optimizer stats collection(2)aut 阅读全文

posted @ 2013-08-10 17:52 FangwenYu 阅读(413) 评论(0) 推荐(0)

诡异的 "Error 45 initializing SQL*Plus - Internal error"

摘要：诡异的 "Error 45 initializing SQL*Plus - Internal error" 阅读全文

posted @ 2013-01-18 20:49 FangwenYu 阅读(6690) 评论(0) 推荐(0)

Buggy Buggy "NULL"

摘要：NULL值在predicate和constraint中的不同处理方式阅读全文

posted @ 2012-09-07 10:41 FangwenYu 阅读(232) 评论(0) 推荐(0)

rowid paging benefit from 11g new feature

摘要：rowid paging benefit from 11g new feature 阅读全文

posted @ 2012-09-03 21:16 FangwenYu 阅读(360) 评论(0) 推荐(0)

Creating Java Stored Procedure

摘要：A simple example to create java stored procedure in oracle 阅读全文