Oracle DB Development

SQL Access to the alert-log in 11g and an oddity

Quite a while ago I wrote about how to seup the alert log as an external table. Since then 11g has been introduced and is now widely used. It of couse changes the location and makes the alert log an xml file.

While it is possible to select from it using xml functions like Laurent Schneider does here, it is still a bit cumbersome.

Tanel Poder (@TanelPoder) found a nicer way by using X$DBGALERTEXT which does a really nice job of parsing the xml-file into a lot of different columns. A friend at work, Daniel Ekberg, let me know about it a while back. I just never got around to looking into it until today.

It is very nice but there is one slight issue with it. It is X$ and thereby only available to SYSDBA. That can of course be solved with a view and proper grants and synonyms. However, views on X$ can cause some issues during upgrades so such views should probably be dropped before upgrading.

While not documented, this is a neat way to gain access to a lot of information from the xml.log (alert-log).

OOW 2010 Develop Keynote

Yes, this post is a little out of order as it clearly didn't take place after the Thursday afternoon sessions. I missed it during the conference so I had to catch up on it later on the on demand site. I thought it was interesting enough to write up a few notes.

It was held by Tom Kyte and the subject was "What's new in database development". It'd be more correct to say Oracle development than database development as he covered just about any area that Oracle focuses on.

He started with APEX and spent a lot of time on it. The coverage APEX gets in general sessions and the number of really good APEX sessions speaks volumes about how strong APEX is becoming within the Oracle development technologies.

Tom shared a little background of how APEX was built by Mike Hitchwa when Mike set next to Tom and wrote the initial code for APEX. Anyone that has been impressed with the way bind variables are handled in APEX got their explanation for why. Tom has relentlessly been preaching about how to to it and the issues caused when not done well. So it all makes sense when you hear that it was Tom who wrote the initial code for bind variable handling in APEX.

Tom went on to say that they are seeing a lot of momentum behind APEX right now. The catch phrase he used to explain why it grows fast in popularity was "Easy architecture, easy to deploy, and easy to run".

Tom then spent some time talking about performance of APEX as a lot of people still thinks it is not able to handle enterprise level system demands.

The site apex.oracle.com that is used to run all the applications people create on Oracles hosted apex "test and demo" site has a surprisingly small computer running it. The specifications for it is:

• Poweredge 1950
• 2 Dual core Xeon 2.33 Ghz
• 32 GB Ram
• Cost : $4,300 (in 2007)
• Runs 11G database

Not a very big computer to serve a site that provides support to anone who wants to try APEX.

Tom shared som of the numbers for what apex.oracle.com is used for.

• They had 3.5 million views (pages loaded and processed) last week.
• Distinct users accessing during the week: 3028
• Total workspaces :9062
• Applications: 32776

I'd think most "enterprise" systems would have less demand than that.

Some of the biggest things on apex.oracle.com are:

• SQL Developer updates 800K hits /week
• Pro MED (Prodution system) 770K hits / week
• Asktom 250K-1000K hits / week
• APEX Appbuilder 238K hits / week
• JDeveloper updates 175K hits / week

Impressive to serve all of that from a small(ish) computer.

Tom then shared some key features from the 4.0 release.

Websheets

Designed for the enduser and designed for webbased content sharing. A solution that allows endusers to stop mailing exceldocuments around would be a good thing...

Dynamic Actions

Declarative client-side behavior. It is integrated in the framework. Uses JQuery.

This allows using common javascript function for handling advanced user interface improvements. From validations to drag and drop and more.

Team Development

Allows you to manage the application development process within APEX. This makes APEX able to be used by large development projects. It has built in end-user feedback. When a user has a problem they can tell you directly in the application and it feeds into the team development features.

Oracle APEX Listener

Built in Java.

It is a good alternative to mod_plsql and it is certified against WLS and Glassfish.

After that long piece on APEX, Tom went through som improvements for other technologies.

SQL Developer

The datamodeller is now free. It will now come with the product and will be supported with the database (just like SQL Developer itself).

It has real-time SQL monitoring. It will allow you to see what part of the execution plan Oracle is currently spending time in for a SQL. This exists in Enterprise Manager, but this gives the insight to many more as EM often is just used by the DBAs.

It can now find the SQL trace file and display the contents graphically in SQL Developer. This ought to make trace files much more accessible to developers.

It has support for AWR and ASH reports and has added developer specefic things that are not available in the other AWR/ASH aware tools.

A hierarchical profiler is now also included to allow you to see what functions calls which in a run of PL*SQL code.

SQL Developer now used PL/SCOPE data to show information about where variables are defined and used, This is something that has been added to the database and can alays be accessed with SQL, but it is more convenient to have it hooked into the development tool.

They have also added a DBA Navigator that allows DBAs to access most things they deal with in the database. Most objects (such as extents and tablespaces) can be seen and modified.

An interface for DBMS_SCHEDULER has been added. It is supposedly a much nicer way to configure jobs than to do it by have, which can be both tedious and complicated.

Another neat feature is that auto tracing has been improved to not only allow tracing of a statement, you can now trace two statements and see a comparison report of the tracing so you can compare them. Since this usually has been done with Toms "Runstats" package, I'd assume this feature has Toms fingers all over it.

ODP.Net

It is free and provides native access to the database. It has statement caching (on the client side) and will support TimesTen in 11.2.0.2.

I'm not a .Net person at all , but it sounds as if this provides a lot of benefits both in use and in performance. If you work with .Net, then you will want to take a look at all the things Oracle provides in this area.

Java

There is a Universal Connection Pool for all technologies using connection pools to use. This is supposed to reduce the overhead caused by having several connection pools.

For Secure Files there has apparently been a performance issue dealing with very large files, my understanding from Toms presentation is that it resulted in double buffering. Now there is Zero Copy which sounded as if it would remove all buffering and thereby improve the speed significantly.

Database Improvements

Tom focused on the optimizer and on developer related topics as this was a Develop keynote.

Tom showed how the optimizer could detect a three-way join that was not needed. It was a fairly complicated situation, but the optimizer can apparently completely skip accessing tables now if they are not needed for the end result.

PL*SQL

Edition based redefinition is available in a editions of 11G. Tom thinks this is the killer feature of 11G, and says that it may be the first time the killer feature is available in all editions and with no additional licensing requirements.

It allows live changing of code (PL and views). Live changing of data can already be done with online redefinition and online actions on indexes.

The process now is:

• Create new edition
• Test new edition of the code while users still use the old.
• Two options for rolling out
  • Let new sessions use the new one and allow old to keep using the old edition.
  • Switch everyone over to the new when the system is "idle". Takes just seconds.

That was the end of Toms presentation. He covered a lot of technologies, even some that are not mentioned above (like Ruby). WHat I think is interesting is what wasn't mentioned at all.

The fist one that comes to mind is JDeveloper. It has not become very popular with Java purists and it is not mentioned at all. There are some rumors of it being de-emphasized by Oracle as how you work with it seems to be very far from how most Java projects want to organize their builds and deployments.

Next interesting omission is the technology mostly integrated with JDeveloper. No mention at all on the Oracle Develop for their key Java development framework. ADF did not get any love at all and that is not true just for this presentations, there were very few mentions of it in any of the presentations I attended. True, I did not seek out ADF sessions, but virtually every single presentation on non APEX technologies found a way to talk about APEX, the oposite was true for ADF. Even when you felt that someone was building up to a plug for ADF, they never went there.

The lack of love for ADF and JDeveloper may mean that they are not considered critical to Oracles success anymore. I assume ADF was used to build the fusion applications which would mean that the tool and product is probably not going away, but could it mean that they are primarily being focused for large product development and not something that is good for custom development projects?

Personally it feels as if ADF is now essentially becoming a tool used when integrating with Oracle (fusion) Apps or Oracle SOA Suite. I'm not sure a custom development project would end up using ADF. Of course there will be exceptions to that, but they will probably be fewer and fewer.

It could also be that JDeveloper and ADF starts becoming less and less of something for the customers and more and more of an internal tool at Oracle. I'm sure they have very specialized versions and techniques used in development to help the development of the fusion applications.

On the other hand, it could just be that this wasn't the time for releasing improvements to JDeveloper or ADF. I have trouble convincing myself of that though. The reason is that Oracle now owns Java and if there ever would have nee a reason to show JDeveloper and ADF in its full glory, now would have been the time. By not releasing improvements to what is considered problems with JDeveloper and ADF, they have probably given more momentum to the competing tools. They of course ha another tool in this space now, maybe NetBeans will be the future migration path of JDeveloper and when ADF finds a new home.

OOW 2010 Thursday Morning

The day starts with a presentation b6 Tom Kyte about "What else can you do with system and session data".

Tom starts with reviewing the history of tuning an Oracle database.

The prehistoric era (v5) required writeing debug code as that was the only way to get any information about what the code did.

The dark ages followed (v6) and now Oracle introduces:

• Counters/ratios
• bstat/estat
• SQL Trace
• The first few (7?) v$-views are introduced

In the rainessance era (v7) introduced a few more things:

• The wait event instrumentation was introduced
• Move from counters to timers
• Statspack

The modern era (v10) introduced the tools we prefer today

• DB-Time tuning
• Multiple scoping levels (AWR)
• Always on, non-intrusive
• Bult into the infrastructure - instrumentation, ASH, AWR, ADDM, EM

DBA_HIST_* views is where the historic data is located.

Tom contunued with discussing the metrics and the timemodel and how to join that to get data about them. However, all his presentations are available for everyone and you're better off reading them on his site than getting a summary of it here.

As usual, Tom places his presentations and other things under files on asktom.

The next presentation was Apex debugging and tracing with Doug Gault from Sumneva.

Debug mode is truned off on the app level by default. It neds to be enabled there before it can be used.

Debug data is now written to a table, and not dumped on the webpage as before. It is viewed by clicking view debug in the developer bar in the APEX interface.

Use conditional display to output things only in debugmode (using v('DEBUG') ).

Things that happens on a page after it has been rendered will not be captured. This is things like javascript running on this client.

APEX_DEBUG_MESSAGE is currently undocumented, but the code shows how to use it.

Debugging can be turned on/off on the page programmatically.

Logging from you own code allows you to see what parts of a package call it is that takes the time.

Doug then shows a few different ways to collect and report on the debugdata for a report.

I recommend looking at the presentation for ideas on how to use it and what can be done. Unfortunately this presentation does not seem to be available on the sumneva website at this point. If you are interested in it, send an email to them asking if they are willing to share it on their presenation page. You'd of course want to check their site first to make sure it isn't uploaded between the time I write this and the time you read it.

 

The case for CASE

I've just uploaded my latest article. This time it is a look at the SQL keyword CASE. It's power is often not fully appreciated. It is much more flexible and powerful than you may expect from just taking a quick glance in the official documentation.

The article is located here.

Please post comments and questions here.

Supported version of skip locked?

As Pawel showed in his post some details about how the row scn technology works in specific situations isn't as well documented as you'd wish.

I asked Oracle development to clarify the questions I had and the answer back was both interesting and useful. Every kind of update and lock on a row will make the rowscn for the row/block NULL until the updating/locking transaction completes. That is, any kind of lock and update can be identified when retrieving data.

More interesting is that this can be used to implement "skip locked" which is a feature oracle AQ uses, but it is not supported for use by end users. For a table where rowdependencies is defined, this can now be implemented with "where ora_rowscn is NOT NULL". I don't know exactly how and when I'll use it, but it is good to have this tool when the situation arises. I'm sure it'll come in handy soon enough as discussions about the skip locked feature seems to occur almost on a monthly basis.

I'm on a long vacation so I cannot test this until I come home again. I had some time over this mornings, so I figured it would be a good time to show that the blog isn't completely dead, it's just not too active when I have to choose between talking with friends and family I haven't seen in a couple of years and researching Oracle technologies.

SQL Challenge I - Solution

Both Gary and Philip postd working versions. Gary's didn't work for me when I had the same letter more than one time in the string. Philips did work and the need to deal with each letter as if it is unique can of course be questioned. The intent was for a solution that could handle that and as Philip showed adjusting that is as easy as to just add a distinct.

My version is based on not using analytical functions of which I thought connect by was a part. Looking at it in another way, I wanted something that could be adopted to other databases.

My starting version of the solution would be:

   with v    as (select 'ABC' v from dual)
   ,base as (select substr(v.v,1,1) nv, 1 nn from v
             union all
             select substr(v.v,2,1) nv, 2 nn  from v
             union all
             select substr(v.v,3,1) nv, 3 nn  from v)
  select a.nv||b.nv||c.nv
    from base a, base b, base c
   where a.nn not in(b.nn, c.nn)
     and b.nn not in (c.nn)

What's not to like? I get to use one with construct that takes the output from another with construct as it's input.
The "base" with gives us a result table that has one letter from the input string on each row. I'm then joining that with itself three times (as I have three letter in the string) to get a cartesian product that holds all cominations. It has the valid combinations (where all three letters are used) and invalid ones (where some letters are used more than one time). The last thing is to remove the invalid combinations. I do this by checking if the number I assign to each value (nn) occurs more than one time in the result. For AAA we would have nn for table alias A, B, and C be 1. I only have to check if each value occurs later on in the column list as if it was equal to an earlier one, the test for that earlier one would detect that the same was used.

So it works… Interesting and satisfying at the same time. However, the union is not too lovable. How can we avoid it? Well, the easy way would of course be to use the connect by trick, but as I intended to not use it I'll have to cheat and use anoter unrelated table (view).

   with v    as (select 'ABC' v from dual)
      ,base as (select substr( v.v,rownum,1) nv
                      ,rownum nn from v, all_objects
                 where rownum <= length(v.v))

    select a.nv||b.nv||c.nv

     from base a

         ,base b

         ,base c

    where a.nn not in (b.nn, c.nn)

     and b.nn not in (c.nn) 

I'm usig all_objects which should have more rows than the length of a string you want all combinations. It works, but I still prefer the connect by version if I were to use it. This way it does satisfy the limitation I put up for this.

So while this works, it is not as dynamic as one could want it to be. You need a different SQL if you have a four letter string. It ieasy to change this for that, but it is still annoying to have to have many different ones. An alternative would be to write PL*SQL to generate the SQL and then execute it. While that may be nicer, I wanted a solution that was a single statement.

I did find a way to do it. I'm sure it can be done easier and nicer. Maybe analytic functions would make the SQL faster and easier to understand. However, This way combines XML, with clauses, and dynamic in-line queries. For fancy use of the Oracle database, it's almost optimal… How practical it would be to use this very often and with long strings would have to be tested before getting it into a production scenario.

   with v as (select 'ABC' v from dual)
      ,base as (select substr(v.v,rownum,1) nv
                      ,rownum nn
                  from v
                      ,all_objects
                 where rownum <= length(v.v))       ,sel  as (select 'select ' ||                        substr(max(sys_connect_by_path('a'||
                       nn||'.nv', '||')),3)||' data' a
                  from base
               connect by prior nn = nn - 1
                 start with nn = 1)
     ,frm  as (select 'from ' ||
                      substr(max(sys_connect_by_path(
                      'base a'||nn, ',')),2) a
                 from base
              connect by prior nn = nn - 1
                start with nn = 1)
     ,whr2  as (select 'a'||(nn-1)||'.nn not in('||
                       substr(max(sys_connect_by_path(
                       'a'||nn||'.nn', ', ')),2) ||
                       ')' cond
                      ,max(rownum) rn
                  from base
                      ,v
                 where nn > 1
               connect by prior nn = nn + 1
                 start with nn = length( v.v)
                 group by nn
                 order by nn)
     ,whr  as (select 'where ' || substr(max(
                      sys_connect_by_path(cond, ' and '))
                      ,5) a
                 from whr2
                     ,v
                where not rn = length(v.v)
              connect by prior rn = rn + 1
                start with rn = length( v.v) - 1)
  select extractvalue(t.column_value,'/DATA')
    from sel a
        ,frm b
        ,whr c
        ,xmltable(
          'for $root in $vals
           return $root/ROWSET/ROW/DATA'
           passing xmltype(dbms_xmlgen.getxml(
          'with v    as (select ''ABC'' v
                           from dual)
               ,base as (select substr(v.v,rownum,1) nv
                               ,rownum nn
                           from v
                               ,all_objects
                          where rownum <= length(v.v))'                              ||a.a||' '                              ||b.a||' '                              ||c.a)) as "vals") t; 

The formatting is a bit forced here as I need it to fit in the line size google allows on this blog. I will not explain in detail what I have tried to achieve in this SQL. If you would want me to talk about what I'm doing in a post, leave a comment and I'll try to write it up in a post soon.

In short, I'm generating different pieces of the SQL statement needed in the with clauses and them I'm using that to create the XML document with all these cominations ina single XML document. I'm then using some XML function and XMLTable with an XML Query to get it back out form one row (one XML doc) to multiple rows to get it back to relational data.

The threaad that started me thinking about this was this thread. There are some permutations things there that solves this with pure analytics. But why do this the easy way when you can make it more complicated. Laurent's solution is probably the only one that scales well with longer strings.

I hope you enjoyed this and hopefully even learned something. I know I did, both that Cartesian products can be used in ways I hadn't really thought of and that I need to learn more about analytical functions.

I also learned more about XML function and how to move data in and out of these dynamic in-line queries.

Dynamic in-line queries

I don't know of a better name for this feature. I think this name descibes the function well, even if it may sound overly ambitious. This whole post will be based on a post by Laurent Schneider where he uses XML features to do a select count(*) from different tables and return the result in one result table. It is like a auto generated number of selects that are unioned together.

You can find Laurent's post here. It's a wonderful piece of SQL to do something most of us would probably not have thought of using a single SQL statement for.

The version Laurent uses is:

   select table_name
        ,to_number(extractvalue(xmltype(
            dbms_xmlgen.getxml(
              'select count(*) c from '||table_name))
                  ,'/ROWSET/ROW/C')) count
    from user_tables;

Let's first review what happens in this query. The inner most function is a call to dbms.getxml with a query that will return one row and one value. This sql stateement is created on the fly based on the table name the outer select retrieves from user_tables. The function will of course turn the query result into XML text. The xmltype that wraps the function will convert the XML text into an XML object so XPATH functions can be used. The extractvalue function pulls out the node ROWSET/ROW/C where the two first are given as that is how getxml will return the data. C is the name of the column or in this case the alias assigned in the select statement as the resulting "column" from the count(*) function. The last thing that happens is that the extracted value is converted to a number and it is then returned to the outer select as the result from this function.

The query returns a result set like:

TABLE_NAME                      COUNT

Creating a feed with ORA-00600 errors

Instead of having to look at your different alert logs for ORA-00600 errors frequently, why not have them come to you? This post will, as promised, show the Perl code needed to publish a feed with ORA-00600 errors. This is building on the previous two posts that shows how to create an external table for the alert log and how to pull out all information for an ORA-00600 so each fetch retrieves one the data you're interested in.

The feed I'm using is a RSS 2.0 format. All feeds are fairly closely related so you can change it or provide different ones if you want to. You'll have to look up the different formats and then make the changes you want to this code.

The script I have here is a simplified version that removes all the usual dynamic nature and flexibility with parameters I usually have. This is done for brevity and to focus the script on the task at hand - delivering the ORA-00600 errors to your newsreader soon after they occur.

The script is not pretty and it could be written much nicer with use of modules such as XML::RSS. Unfortunately that module has a chain of dependencies that I didn't want to satisfy, so I'm creating the tags the old fashioned hard coded way. If you are to do a lot feeds with Perl, you will want to get that module installed.

!/usr/bin/perl
require v5.6;
use strict;
use CGI qw(:standard :html3 :netscape);
use CGI::Carp;
use DBI;
use DBD::Oracle qw(:ora_session_modes);

my ($ORACLE_HOME, $DBH);

if ( $ENV{TWO_TASK} ) { undef $ENV{TWO_TASK}; }

$ENV{"ORACLE_HOME"}='/path/to/oracle/install/dir';

my $statusRec;

print 'Content-Type: text/xml' . "\n\n";

print '<?xml version="1.0"?>' . "\n";

print '<rss version="2.0">' . "\n";

print '  <channel>' . "\n";

print '    <title>Oracle ORA-00600</title>' . "\n";

print '    <description>ORA 600 errors</description>' . "\n";

print '    <language>en-us</language>' . "\n";

print '    <copyright>Copyright 2007</copyright>' . "\n";

print '    <managingEditor>email@domain</managingEditor>' . "\n";

print '    <webMaster>email@domain</webMaster>' . "\n";

print '    <generator>script name</generator>';

# Create db connection

$DBH = DBI->connect("DBI:Oracle:host=zzz;SID=zzz;port=nnnn", "alertlog", "alertlog",

    { RaiseError => 1, AutoCommit => 0 })

    || die "Could not connect\n\tError: $DBI::errstr";

my $STH = $DBH->prepare("with alert as

               (select rownum rn

                      ,text_line

                  from alert_log)

            select a.text_line date_msg

                  ,b.text_line file_msg

                  ,c.text_line err_msg

              from alert a inner join alert b

                on a.rn = b.rn - 1

                           inner join alert c

                on b.rn = c.rn - 1

             where c.text_line like '%ORA-00600%'");

$STH->execute() || die "Couldn't execute statement: $STH->errstr";

while($statusRec = $STH->fetchrow_hashref())

{

  print "     <item>\n";

  print "       <title>ORA-600 Occured</title>\n";

  print "       <description>An ORA-00600 has been detected.\n";

  print "<p>\n";

  print " \n";

  print "The following information was logged about the event:\n</p><p>";

  print $statusRec->{"DATE_MSG"}   . "</p>\n<p>";

  print $statusRec->{"FILE_MSG"} . "</p>\n<p>";

  print $statusRec->{"ERR_MSG"}  . "</p>\n" . "</description>\n";

  print "       <author>your name</author>\n";

  print "     </item>\n";

}

$STH->finish();

$DBH->disconnect();

print "  </channel>\n";

print "</rss>";

That is all it takes. This is obviously a CGI script that would run in your web server. If you have one with CGI capabilities configured, you'd place the script there and call it with an url like "http://your.domain/cgi-bin/script_name.cgi". Ask your web admin if you don' know where and how to place this script. If you have your own web server and don't know how to do this, leave a comment and I'll try to give you a few quick hints about how to get it working.

I'm afraid the code above will be truncated by google's new blog interface. The code will still be there so just cut and paste it into your favorite code editor and you'll have all the needed code.

You will probably want to change these lines to something different:

$ENV{"ORACLE_HOME"}='/path/to/oracle/install/dir';

$DBH = DBI->connect("DBI:Oracle:host=...snip...,

...and the following nodes...

copyright

managingEditor

webMaster

generator

author

The first one should point to where you have Oracle installed and the second will be your connection string. If you don't know the port ask your DBA or try the default of 1521. It is the port you have your listener configured to listen on.

There is no guarantee that the code works as is. Every environment is different and the code is clearly not environment proof. If you have problems with it, check your error log for the web server and leave a message if you want my input on what the problem might be.

Enough alert log stuff? Probably. Sorry if you feel I've overdone it and got stuck on this subject for too long. Next post will not even mention the alert log.

If you have APEX or want to wait for 11G where it will be a supported option, you will want to use APEX and pure SQL for this rather than Perl. A good intro to how to do it can be found on asktom.oracle.com. It is written by Sean Dillon and looks well written and easy to follow, it can be found here. I've not tried it myself, but it sounds straight forward and anything from the people behind asktom and APEX at Oracle is usually both easy to understand and easy to implement (relative to the subject's complexity).

Querying the alert log for ORA-00600

Time to expand on the last post. As promised this will be about how to get the ORA-00600 information out of an external table for the alert log. We will use the same user and setup as we had in that post.

Lets first review how an ORA-00600 is represented in the alert log.

   Tue Feb  1 02:09:44 2005
   Errors in file /path/to/trace/file:
   ORA-00600: internal error code, arguments: [1100],
     [0x388F0D990], [0x382253888], [], [], [], [], []

The actual arguments does not matter, I took them from a forum post to just have an example. What we care about for what we're doing here is that the format is one line with a date, one line with a reference to a trace file, and one line specifying the error code (ORA-00600) and the needed arguments (for Oracle support).

Thus, we'll need to find the row with the ORA-00600 and match it up with the two previous rows. To do this we'll return to my favorite SQL key word, the with clause. It lets us get all rows, get a generated unique id per row, and know that the rows we look at will be identical as we're now using the same source. In theory, we could end up with the rows in different order if we joined the actual table with itself. Oracle does not guarantee the order you retrieve data in unless you order it, end we have nothing to order on here.

    with alert as (select rownum rn
                       ,text_line
                   from alert_log)
 select a.text_line date_msg
       ,b.text_line file_msg
       ,c.text_line err_msg
   from alert a inner join alert b
     on a.rn = b.rn - 1
                inner join alert c
     on b.rn = c.rn - 1
  where c.text_line like '%ORA-00600%';

This gives us the alert log message in three columns. We can now process it any way we want. It could be used to create a report or generate an email with your ORA-00600 messages.

However, the actual ORA-00600 shows that we made a mistake when we created the table. It cuts off the text_line after a comma. That is not what we want, we want all data up to the end of the line. So we need to change the definition of the table to make sure we get all of that.

   conn alertlog/alertlog
   drop table alert_log;
   create table alert_log
     (text_line varchar2(255))
     organization external
     (type oracle_loader
     default directory bdump
     access parameters(
     fields terminated by x'10')
     location ('alert_ORCL.log'));

That's better, the default delimiter of comma has been replaced with linefeed (ASCII 10) for UNIX platforms. Replace it with what you need. As long as it is a charcter that will never occur in a text line in your alert log, this will work fine.

Now that we have a select that gets all data for an ORA-00600 in each row it returns, it is easy to operate on that data. This model can of course be used to list other pieces of data from the alert log. One such use could be to report how long time it takes between log switches. That is left as an exercise for the reader.

My next post will show how to use this to create a RSS feed for your ORA-00600. That allows you to within minutes know when you have had an ORA-00600 occur and you get it delivered as a separate feed to your news/blog reader.

SQL Access to the alert log

I'm going to discuss how to get SQL access to your alert log in this entry. I will then build on that to make it even more useful in future posts.

Browsing the alert log can be convenient if you're already on the server. However, it is often not possible or at least not overly convenient. You may find that as the developer DBA you do not have access to the production server, or you have to log in to many different servers to check all your alert logs. Since SQL is the main tool for DBAs and one of the most critical for developers of database driven applications, it would make sense to access the key log for database operations and issues via the same interface and be able to use your SQL tool of choice.

The way to be able to access the alert log with SQL is to define an external table for it. So I'll use this need to write a little about how to create an external table for text file. It's pretty easy and can often be very useful.

create directory bdump as '/path/to/bdump';
create user alertlog identified by alertlog;
alter user alertlog quota unlimited on users;
grant create session, resource to alertlog;
grant read,write on directory bdump to alertlog;

The directory path needs to be what you have "background_dump_dest" set to. You can look the current value up in v$parameter. To be able to do this with one script across databases, you'll want to make this more dynamic with pl*sql such that the directory is retrieved from the database and used to build a dynamic DDL statement.

Now that we have a user with access to our bdump directory, we'll create our alert_log table.

create table alert_log
 (text_line varchar2(255))
 organization external
 (type oracle_loader
  default directory bdump
  location ('alert_ORCL.log'));

This is a minimal create external table statement. There are many more options to use, but we'll leave those alone in this blog post.

The create table statement is pretty straight forward, here's what it will do:

• Creates a table with data that is located external to the database
• Take all data in each line into the column text_line
• Use the normal oracle_loader (SQL*Loader) driver to access the data
• It uses the bdump directory object to specify where the alert log file is located.
• Get data from the file alert_ORCL.log.

That is all it takes. We can now access this table with SQL and use our normal techniques for filtering and aggregating information.

To look at the snapshot too old messages we generated in a previous blog post, we'd use this statement:

select text_line
 from alert_log
where text_line like '%ORA-01555%';

TEXT_LINE