Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 3 ■ FILES 85 _qerixAllocate+4155 _qknRwsAllocateTree+281 _qknRwsAllocateTree+252 _qknRwsAllocateTree+252 _qknRwsAllocateTree+252 _qknDoRwsAllocate+9 ... Here we see a couple of important pieces of information. First, we find the SQL statement that was executing when the internal error was raised, which is very useful for tracking down what application(s) was affected. Also, since we see the SQL here, we can possibly start investigating possible work-arounds—trying different ways to code the SQL to see if we can quickly work around the issue while working the bug. Furthermore, we can cut and paste the offending SQL into SQL*Plus and see if we have a nicely reproducible test case for Oracle Support (these are the best kinds of test cases, of course). The other important pieces of information are the error code (typically 600, 3113, or 7445) and other arguments associated with the error code. Using these, along with some of the stack trace information that shows the set of Oracle internal subroutines that were called in order, we might be able to find an existing bug (and work-arounds, patches, and so on). For example, we might use the search string ora-00600 12410 ksesic0 qerixAllocate qknRwsAllocateTree Using MetaLink’s advanced search (using all of the words, search the bug database), we immediately find the bug 3800614, “ORA-600 [12410] ON SIMPLE QUERY WITH ANALYTIC FUNCTION”. If we go to http://metalink.oracle.com and search using that text, we will discover this bug, see that it is fixed in the next release, and note that patches are available—all of that information is available to us. I find many times, the error I receive is an error that has happened before and there are in fact fixes or work-arounds for it. Trace File Wrap-Up You now know the two types of general trace files, where they are located, and how to find them. Hopefully, you’ll use trace files mostly for tuning and increasing the performance of your application, rather than for filing iTARs. As a last note, Oracle Support does have access to many undocumented “events” that are very useful for dumping out tons of diagnostic information whenever the database hits any error. For example, if you believe you are getting an ORA-01555 when you absolutely feel you should not be, Oracle Support can guide you through the process of setting such diagnostic events in order to help you track down precisely why that error is getting raised, by creating a trace file every time that error is encountered. Alert File The alert file (also known as the alert log) is the diary of the database. It is a simple text file written to from the day the database is “born” (created) to the end of time (until you erase it). In this file, you will find a chronological history of your database—the log switches; the internal errors that might be raised; when tablespaces were created, taken offline, put back online;
86 CHAPTER 3 ■ FILES and so on. It is an incredibly useful file for seeing the history of a database. I like to let mine grow fairly large before “rolling” (archiving) them. The more information the better, I believe, for this file. I will not describe everything that goes into an alert log—that is a fairly broad topic. I encourage you to take a look at yours, however, and see the wealth of information that is in there. Instead, in this section we’ll take a look at a specific example of how to mine information from this alert log, in this case to create an uptime report. I recently used the alert log file for the http://asktom.oracle.com website and to generate an uptime report for my database. Instead of poking through the file and figuring that out manually (the shutdown and startup times are in there), I decided to take advantage of the database and SQL to automate this, thus creating a technique for creating a dynamic uptime report straight from the alert log. Using an EXTERNAL TABLE (which is covered in much more detail Chapter 10), we can actually query our alert log and see what is in there. I discovered that a pair of records was produced in my alert log every time I started the database: Thu May 6 14:24:42 2004 Starting ORACLE instance (normal) That is, a timestamp record, in that constant fixed width format, coupled with the message Starting ORACLE instance. I also noticed that before these records there would either be an ALTER DATABASE CLOSE message (during a clean shutdown) or a shutdown abort message, or “nothing”—no message, indicating a system crash. But any message would have some timestamp associated with it as well. So, as long as the system didn’t “crash,” some meaningful timestamp would be recorded in the alert log (and in the event of a system crash, some timestamp would be recorded shortly before the crash, as the alert log is written to quite frequently). I noticed that I could easily generate an uptime report if I • Collected all of the records like Starting ORACLE instance % • Collected all of the records that matched the date format (that were in fact dates) • Associated with each Starting ORACLE instance record the prior two records (which would be dates) The following code creates an external table to make it possible to query the alert log. (Note: replace /background/dump/dest/ with your actual background dump destination and use your alert log name in the CREATE TABLE statement.) ops$tkyte@ORA10G> create or replace directory data_dir as '/background/dump/dest/' 2 / Directory created. ops$tkyte@ORA10G> CREATE TABLE alert_log 2 ( 3 text_line varchar2(255) 4 ) 5 ORGANIZATION EXTERNAL
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Expert Oracle Database Architecture
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Contents Foreword . . . . . . . . .
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■CONTENTS v Block Buffer Cache .
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■CONTENTS vii ■CHAPTER 9 Redo a
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Foreword “THINK.” In 1914, Thom
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About the Technical Reviewers ■JO
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Introduction The inspiration for th
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Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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