Back in May 2006, I have started my blog using the Blogger platform and one month later moved it to my own website using Wordpress. Couple month later, I joined Pythian and, since then, the vast majority of my blogging activities has been on the Pythian Group Blog.

The Pythian blog has grown significantly since then and many more excellent authors started blogging there. While the Pythian blog was mostly focused on Oracle database just a couple years ago, it’s has got very broad coverage now and is including MySQL, SQL Server and Oracle databases as well as Oracle Application Server, Oracle eBusiness Suite and other enterprise software. While I think this is a great opportunity to entend your area of interests, it might be just too much for some as few people already complained and unsubscribed to avoid being overwhelmed with information. That was painful to hear!

First of all, I should say that there is a way to subscribe only to a selected category or a single author — just add /feed/ at the end of pretty much any page. For example, all my blog posts can be seen using URL http://www.pythian.com/blogs/author/alex and RSS feed URL would be http://www.pythian.com/blogs/author/alex/feed/. Likewise, the Oracle category RSS feed is http://www.pythian.com/blogs/category/oracle/feed/. (more…)

Recently, I had an opportunity to tune latch contention for cache buffers chain (CBC) latches. The problem was high CPU-usage combined with poor application performance. A quick review of the statspack report for 15 minutes showed a latch-free wait as the top event, consuming approximately 3600 seconds in an 8-CPU server. CPU usage was quite high, which is a typical symptom of latch contention, due to the spinning involved. v$session_wait showed that hundreds of sessions were waiting for latch free event.

SQL> @waits10g

   SID PID     EVENT         P1_P2_P3_TEXT
------ ------- ------------  --------------------------------------
   294  17189  latch free    address 15873156640-number 127-tries 0
   628  17187  latch free    address 15873156640-number 127-tries 0
....
   343  17191  latch free    address 15873156640-number 127-tries 0
   599  17199  latch: cache  address 17748373096-number 122-tries 0
               buffers chains
   337  17214  latch: cache  address 17748373096-number 122-tries 0
               buffers chains
.....
   695  17228  latch: cache  address 17748373096-number 122-tries 0
               buffers chains
....
   276  15153  latch: cache  address 19878655176-number 122-tries 1
               buffers chains

I will use a two-pronged approach to find the root cause scientifically. First, I’ll find the SQL suffering from latch contention and objects associated with the access plan for that SQL. Next,I will find the buffers involved in latch contention, and map that back to objects. Finally, I will match these two techniques to pinpoint the root cause.

Before I go any further, let’s do a quick summary of the internals of latch operations.

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Welcome to the 107th edition of the Log Buffer. My name is Keith Murphy and I am a MySQL database administrator for the Pythian Group. In addition, I am the editor of MySQL Magazine. This is my second go for the Log Buffer, so I must be doing something right!

This week for the open source world brings OSCON in Portland Oregon. There are plenty of MySQL people present and there have been more posting this week from these realms than normal. Also, Lewis Cunningham, among others, posted news that EnterpriseDB released the results of their open source survey at OSCON. The 451 CAOS Theory published their thoughts on the survey.

Of interest to all DBAs is John Duncan’s post about what is called the “five minute rule”. This was introduced in 1987 by Jim Grey. And finally, before we dive into the specific server news, here is a post on Facebook’s project to build a distributed database similar to Google’s BigTable.

MySQL News:

Friday saw the release of the summer issue of MySQL Magazine. The highlights of the issue include the first annual MySQL Usage Survey. The magazine is available here. Peter, over at Percona, shows some initial benchmarks for the latest version (0.9.8) of Sphinx. If you aren’t familier with Sphinx, it is a full text search engine that easily integrates with MySQL.

Probably the biggest news this week was the announcement by Brian Aker of “Drizzle”. It is what amounts to a slimmed down version of MySQL server. These comments are from his initial post “Stored Procedures, Views, Triggers, Query Cache, and Prepared Statements are gone for now.” Interesting. My co-worker, Sheeri K. Cabral, posted a video of Brian Aker talking about the Drizzle project at this week’s OSCON. Monty Widenius writes a good summary how Drizzle can/might integrate with the MySQL “ecosphere” at large. It was very good to hear Monty say that Sun management is encouraging this project. There has been some other interesting posts about this as well including Arjen’s thoughts, and Paul McCullagh’s. Brian Moon gives a very thoughtful view on how Drizzle could potentially fit in at dealnews. While I could probably fill up the entire Log Buffer with links to post about Drizzle, I better leave it at that.

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1, 2, 3, 4, 5, 6, 9, or 10. It ain’t no Feist song, but she got it right. Notice that she mentions no 7 or 8 in it. Well, that is also true for version support in release 1.21 of DBD::Oracle.

With some of the new functionality that was introduced in DBD::Oracle 1.21, you can no longer use the Oracle 7 and most early 8 clients to build DBD::Oracle.

I hope this little table will help you choose which version of DBD::Oracle is right for you.

As there are dozens and dozens of different versions of Oracle’s clients, I did not bother to list any of them, just the major release versions of Oracle that are out there.

Note that one can still connect to any Oracle version with the older DBD::Oracle versions. The only problem you will have is that some of the newer OCI and Oracle features available in later DBD::Oracle releases will not be available to you.

So to make a short story a little longer:

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There seems to be a bug in DBD::Oracle’s execute_array when working with 11g.

If you tell DBD::Oracle to autocommit, it seems that in 11g this commit will not take place when an error occurs during the processing of one of the tuples that you passed into execute_array. So given this table:

CREATE TABLE test_array (
	    row_1 INTEGER NOT NULL,
	    row_2 INTEGER NOT NULL,
	    row_3 INTEGER NOT NULL)

the following code will result in no records being added to the db.

# create a database handle
my $dbh = DBI->connect('dbi:Oracle:','xxx@xxx','xx',{
	RaiseError			=> 1,
	PrintError			=> 0,
	ShowErrorStatement		=> 1,
	AutoCommit			=> 1

}) || die "Unable to establish connection with Oracle server: $DBI::errstr";

my $rv;
my @var1         = (1,1,1,1,1,1,1,1,1,1);
my @var2         = (2,2,2,2,'s',2,2,2,2,2);
my @var3         = (3,3,3,3,3,3,3,3,3,3);

my $tuple_status = [];
my $dumped ;
my $rows = [];

$sth->execute_array(
        {ArrayTupleStatus => $tuple_status},
          \@var1,
          \@var2,
          \@var2,
   );

The workaround is to set AutoCommit => 0 and then use $dbh-->commit() after the statement.

So far, the jury is out whether this is a bug only in 11g, but as this code works correctly in 9 and 10 (it adds the 9 rows), it seems likely. I have noted the bug here: http://forums.oracle.com/forums/thread.jspa?messageID=2663832#2663832.

Greetings from Wisconsin! Welcome to the 106th edition of the Log Buffer. Mr. Edwards is on a brief holiday and kindly asked me to fill in for him. So join me as we take a tour of some of this week’s database blogging activity.

I’d like to start by sharing the story of MySQL engineer Andrii Nikitin’s young son, Ivan. The short story is that Ivan is in need of a bone marrow transplant and that would also require travelling outside of their native Ukraine for the procedure. The family is asking for donations to cover the cost of the operation and trip, so please consider donating via the previous link.

Now, moving on to the database topics, we begin with my own area of (relative) expertise, Oracle. The big news this week is the July 2008 CPU, or Critical Patch Update, which Oracle releases quarterly. The Integrity blog has a nice summary of what’s included in this latest patchset. I’m sure plenty of you will be heading to Oracle OpenWorld 2008 as well, and OTN’s Justin Kestelyn announced a community preview page with some sneak peeks of what to expect (spoiler: beer!).

In a quick round-up of Oracle 11g topics, Amit Bansal at AskDBA.org has a nice guide for installing Oracle 11g on Solaris 10. Meanwhile, Oracle performance guru (and fellow Wisconsin native) Greg Rahn makes a great case for using incremental global statistics on partitioned tables. I see that Tim Hall has taken a break from reviewing summer blockbusters to write up a nice article on AWR baseline enhancements in Oracle 11gR1, and Alex Nuijten at AMIS has a nice presentation on using Oracle 11g’s virtual columns to clean up your data model.
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Building High-Performance Drivers for Oracle Database 11g: OCI Tips and Tricks (PDF). I had the opportunity to have an early look at this white paper by Luxi Chidamdaram.

The paper goes over what needs to be done to use OCI effectively, especially in a web environment. The step-by-step approach taken in this document is very readable and the well explained code snippets make it a very good reference — great for comparing your code to the “proper” way to do it.

The novice OCI programmer will find the initial sections of great benefit, as it takes a lot of mystery out of OCI programming. For the more advanced OCI-head, the document is full of good examples of how to manage connections, sessions, and pooling–with an examination of what type of pooling is needed in a given situation.

One highlight for me was the section on database events, which are covered very effectively with some practical examples.

In short, this white paper is a must-read for both the OCI master and the novice, with some great pointers on how to use what is already in OCI and what is new in 11.

The latest quarterly update came out this morning. There are oh-my-god smoking guns this time, but several medium-important patches:

CVE-2008-2607: Vulnerability in DBMS_AQELM (Advanced queueing package for e-mail and HTTP notifications)
CVE-2008-2613: Vulnerability in DBMS_SCHEDULER, requiring access to a local user in the oinstall group for exploitation
CVE-2007-1359: Remotely-exploitable vulnerability in Oracle App Server. This is an issue in the ModSecurity application firewall that was originally reported in March 2007 that allows some security checks to be bypassed given a specially-formatted string. The original advisory is here.
CVE-2008-2589: PL/SQL injection flaw in Oracle Portal. Details were posted to the full disclosure list in conjunction with the patch
CVE-2008-2594 and CVE-2008-2609: These look like two more injection flaws in Portal.

If you’re running Oracle Collaboration Suite, note that the patch blows away the login and logout pages (oops!). MetaLink note 445172.1 has info on how to restore the pages post-patch.

Is your database in archive log mode?

Is your database in flashback mode?

Have you defaulted your archive location to the flash recovery area?

Is your ORACLE_SID lowercase?

Do you use SQL BackTrack?

If your answer is yes to all these questions then beware!

There is a bug in SQL BackTrack (at least in version 6.8) that prevents your backing up of the archive logs from the flash recovery area. This will result in the inability to recover from any online backups that you have taken if you somehow lose those archive logs.

You do not receive any obvious errors when doing the backup but, if you are observant, you may spot the fact that the backup report does not show that it backed up any archive logs. To really check whether you are suffering from this problem then you need to check the $DTBASE/obacktrack/log/datatools.log. This is the log that gets written whenever any SQL BackTrack command is run. You will see an error such as

17:29:16.61 obacktrack[839826](2835/oramisc.cpp): Unable to open directory: '/home/oracle/data/test/test/archivelog'

You will know if you have been caught by this bug when you try to restore and you get messages that look something like this.

BMCBKO4802051E: The following Oracle error occurred during
BMCBKO4802051E: SQL-BackTrack processing : 'ORA-01195: online backup of file 1 needs more recovery to be consistent'
BMCBKO4802051E: The following Oracle error occurred during
BMCBKO4802051E: SQL-BackTrack processing : 'ORA-01110: data file 1: '/home/oracle/data/test/system01.dbf''
BMCBKO4805906E: Unable to perform recovery.

The problem arises when Oracle creates a directory in the flash recovery area that correspond to the database name. This directory is in uppercase. So, in my case, my ORACLE_SID is test and the init.ora parameter db_recovery_file_dest='/home/oracle/data/test'.

Oracle creates the directory
/home/oracle/data/test/TEST.

However when SQL BackTrack sees that the archive location is defaulted to the flash recovery area it tries to look in the directory
/home/oracle/data/test/test.

This fails … silently!

There are 2 workarounds to this issue that I have tested.

1. Create a symbolic(soft) link to point to the real directory using ln -s
2. Explicitly set the archive location using the init.ora parameter log_archive_dest_n

The workaround suggested by BMC (the supplier of SQL BackTrack) is to change the database name to uppercase. This will work too, but I haven’t tested it.

This week, database blogs seemed to talk about conforming to stereotypes as well as breaking them.

Fulfilling the stereotype of Microsoft software being unsecure, Microsoft released a very important SQL Server update that Aaron Bertrand notes patches “four elevation of privilege vulnerabilities.” That’s right, not one, not two, but four!!! At least there is a patch now……go forth and patch! Usually it is MySQL that throws ambiguous warnings or errors which are not an accurate representation of the actual error, but Bertrand also notes that there is A Little Management Studio Oops.

Contrary to stereotype, Microsoft is giving away content with NO DRM! Kalen Delaney asks, Did You Know the History of SQL Server? and shares a link to a chapter from a book on SQL Server 2000 in the Inside SQL Server series.

The PSS SQL Escalation Services team has fought many times about SQL Server I/O Bottleneck, I don’t have one, YES YOU DO! The team gives some reminders about how to interpet averages properly.

Allen White asks about Tools for the Reluctant DBA — that is, a programmer or administrator so good at databases that they were promoted to DBA, but may not actually want the job. Check out the comments and add your own.

Tibor Karaszi shares his stored procedure to find physical index details. Now you can use one stored procedure does what a stored procedure plus 3-4 tables ordinarily does.

But wait! There are some more updates!

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