Before/After Trigger efficiency
Something changes continuously... and trigger efficiency too :). Please compare Oracle statement about triggers (see "Note" about trigger efficiency) Oracle 9i, Oracle 10g and Oracle 11g. I`ve tested...
View ArticleASH buffer size
An undocumented feature is shown in modern Oracle version alert log For example: Active Session History (ASH) performed an emergency flush. This may mean that ASH is undersized. If emergency flushes...
View Article"PL/SQL lock timer" wait event is not written into ASH...
Recently I investigated some database lock issue by digging into ASH data. I accidentally found that while session is in 'ACTIVE' state and 'WAITING' on "PL/SQL lock timer", no rows is added into ASH....
View ArticleSQLPLUS ARRAYSIZE and LOB
SQLPLUS ARRAYSIZE drops to 1 if your query select list contains LOB column(s). Extended SQL Trace file contains following rows for such queries (on my 11.2.0.3 Linux box) FETCH...
View ArticleFOR UPDATE SKIP LOCKED
One new thing I`ve learned from recent PL/SQL Challenge quiz is about how SELECT FOR UPDATE SKIP LOCKED works. It does not really lock rows on EXEC phase of query execution (open cursor), when...
View ArticleMaterialize subquery on Active DataGuard
Due to some bug Oracle can fail to materialize subquery from with ... as clause on Active DataGuard with error ORA-00604: error occurred at recursive SQL level 2 ORA-16000: database open for read-only...
View ArticleDo not use instance_id attribute of dbms_scheduler
You must not use dbms_scheduler.set_attribute('YOUR_JOB', 'instance_id', ); for your production system. If DBA makes some maintenance on your job`s RAC node, the job will just not run during that. So,...
View ArticleUnderscore (hidden) parameters in Multitenant database
It is pretty usual when your application needs some underscore (hidden) parameter to be set. But what can happen in new Multitenant database. [oracle@ora12c ~]$ sqlplus / as sysdba...
View ArticleWhy you don't want to parse clob using instr/substr functions
A very strange issue we have hit recently with a report which completion time could suddenly rise two or three times and then drop to some normal half an hour. The report is a pretty complex query...
View ArticleIncluding files in SQL*Plus script
Do you know that @ (at sign) can also work as an include directive? Suppose you have a script for getting your session statistics from v$mystat. But you need a particular list of statistics....
View ArticleHow much redo data does you query generate (not about delayed block cleanup)
I want to show a tiny effect of materializing factored subquery, which can lead to huge redo generation. It is also a good time to taste new feature of defining PL/SQL function in the WITH clause. But...
View ArticleHow many times is pl/sql function called
Recently, a query caught my eye with some strange overuse of resources (LIO in that case). As usual, there were several calls of pretty complex pl/sql user-defined functions. Also an analytic function...
View ArticleSwallowing exceptions
Have you heard about Oracle can hide some exceptions raised from user code? One well-known situation is described here. But there is one more case I've just found. Try this code: create or replace...
View ArticleMERGE statement can fail with ORA-00001: unique constraint violated
How can MERGE statement fail with ORA-00001: unique constraint violated if all other things have been done right? I mean both source and target tables have primary key constraints and all columns from...
View ArticleFlashback to Guaranteed Restore Points with Flashback Logging Disabled does...
As it appeared, flashback to Guaranteed Restore Points with Flashback Logging Disabled does not require redo logs. Indeed, restore point is made during database is mounted, and it does not need any...
View ArticleSQL Monitoring Report History does contain predicate information
It can be extracted pretty easily using the following queries: insert into plan_table (statement_id, plan_id, timestamp, remarks, operation, options, object_node, object_name, object_alias, id,...
View ArticleHow to load big text file into CLOB via SQL*Plus
From time to time a need to load a long text file with XML or even long PL/SQL script arises. And the only tool available is SQL*Plus. As it appeared, it is very simply, if "include script" feature is...
View ArticleNot for APEX guru: Select All/Deselect All in APEX 5
Recently I realized that I need to implement Select All/Deselect All feature for some dynamically generated checklist. Google search overwhelmed me with a vast number of inconvenient and unclear...
View ArticleWrong result when hierarchical query uses rownum filter and subquery filter...
Here is a test case to reproduce the issue. It uses well-known EMP and DEPT tables. If you need a script to create and populate it, see sql-script at the end of this article. Additionally, loopback...
View ArticleSQLPATH environment variable length limit
I heavily use lots of sql scripts spread across several folders. Recently I started some reorganization of that directories to meet new needs of SQLcl (I'm testing it now in order to put it in my tool...
View ArticleBind variable peeking. Part 2.
As Jonathan Lewis wrote: "bind variable peeking is always done, even if histograms are not generated", so be prepared, your plan can be changed without any warning. Let me show the following example:...
View ArticleAPPEND hint placement
It is pretty surprising, that APPEND hint can be placed not only after INSERT keyword but also after SELECT keyword of a subquery. Check these execution plans: SQL> create table tab1 as select *...
View ArticleAn ORA-07445 troubleshooting case
When somebody adopts fresh Oracle releases, she or he will certainly hit some fresh bug, which no one has registered or described before. And there is no choice except trying to dig deeply into...
View ArticleAPEX at Always Free Oracle Cloud Tier with Social Sign-on
There are plenty of articles on the Internet, which describe how to make APEX social. I tried this one for my APEX at an Always Free ATP Database. Of course, I used my domain name to access my APEX...
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