MySQL Test Creator - wrapping up a Summer of Code experience

I talked about this matter already, but now it's time to wrap up.
The Summer of code is over, and the project I have mentored is finished, with a new tool as its outcome, the MySQL test creator.

The student who developed this tool, Charlie Cahoon, did a decent job. All in all, considering that it was his first serious developing experience, he got an excellent result. The maturity stage is still alpha, but he did the breakthrough work to get the development of this tool in the right track.

What do we have in hour hands? A tool that will speed up and make easy the writing of test scripts, during a normal session with the MySQL client. It means that you will fiddle with the database in your usual way, and the test creator will work in the background, writing a test script with its corresponding result file.
Its features include

• starting, stopping and resetting the background script creation;
• using loops;
• removing errors from the script;
• undoing the last command;
• showing the test script.

Let's see an example.

mysql> start;
+------------------------+
| TEST CREATOR           |
+------------------------+
| Testing has started... |
+------------------------+
1 row in set (0.00 sec)

mysql> create table t1 (id int);
Query OK, 0 rows affected (0.01 sec)

mysql> set @counter = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> start_loop myvar 100;
+-------------------------+
| TEST CREATOR            |
+-------------------------+
| Beginning loop creation |
+-------------------------+
1 row in set (0.00 sec)

mysql> set @counter = @counter + 1;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1 values (@counter);
Query OK, 1 row affected (0.00 sec)

mysql> stop_loop;
+--------------------------------+
| TEST CREATOR                   |
+--------------------------------+
| Executed 2 queries X 100 times |
+--------------------------------+
1 row in set (0.02 sec)

mysql> select count(*) from t1;
+----------+
| count(*) |
+----------+
|      100 |
+----------+
1 row in set (0.00 sec)

mysql> stop;
+---------------------+
| TEST CREATOR        |
+---------------------+
| Testing has stopped |
+---------------------+
1 row in set (0.00 sec)

mysql> view test;
+-----------------------------------+
| Test File                         |
+-----------------------------------+
| --disable_warnings                |
| DROP TABLE if exists t1;          |
| --enable_warnings                 |
| create table t1 (id int);         |
| set @counter = 0;                 |
| let $myvar = 100;                 |
| while ($myvar)                    |
| {                                 |
| set @counter = @counter + 1;      |
| insert into t1 values (@counter); |
| dec $myvar;                       |
| }                                 |
| select count(*) from t1;          |
+-----------------------------------+
13 rows in set (0.00 sec)

If you have ever tried to create a loop in mysqltest language, you know what a time saver this tool will be.
Another example. Getting rid of errors:

mysql> start;
+------------------------+
| TEST CREATOR           |
+------------------------+
| Testing has started... |
+------------------------+
1 row in set (0.00 sec)

mysql> select 1 as info;
+------+
| info |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql> select 2 as info;
+------+
| info |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

mysql> select this is wrong;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'wrong' at line 1
mysql> view test;
+-----------------------+
| Test File             |
+-----------------------+
| connection con55;     |
| select 1 as info;     |
| select 2 as info;     |
| --error 1064          |
| select this is wrong; |
+-----------------------+
5 rows in set (0.00 sec)

mysql> discard_last;
+-------------------------------+
| TEST CREATOR                  |
+-------------------------------+
| Last query has been discarded |
+-------------------------------+
1 row in set (0.00 sec)

mysql> view test;
+-------------------+
| Test File         |
+-------------------+
| connection con55; |
| select 1 as info; |
| select 2 as info; |
+-------------------+
3 rows in set (0.00 sec)

mysql> select 3 as info;
+------+
| info |
+------+
|    3 |
+------+
1 row in set (0.00 sec)

mysql> wrong;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'wrong' at line 1
mysql> discard_last;
+-------------------------------+
| TEST CREATOR                  |
+-------------------------------+
| Last query has been discarded |
+-------------------------------+
1 row in set (0.00 sec)

mysql> view test;
+-------------------+
| Test File         |
+-------------------+
| connection con55; |
| select 1 as info; |
| select 2 as info; |
| select 3 as info; |
+-------------------+
4 rows in set (0.00 sec)

mysql> stop;
+---------------------+
| TEST CREATOR        |
+---------------------+
| Testing has stopped |
+---------------------+
1 row in set (0.00 sec)

There are still a few glitches to take care of, but the results so far are really great!

How to hijack a Linux + MySQL server

I hope I got your attention with the title. The politically correct term should be "how to redirect MySQL traffic on Linux", but you probably wouldn't have noticed.
The scenario is this. You want to switch servers without need for the clients to change connection parameters.
Why would you want to do this? Some reasons:

• You want to test a new server version, which you installed to listen to port 13306, and you want to do it without modifying the applications parameters;
• You ant to use MySQL Proxy on port 4040 to log the traffic for a while without restarting the server, in order to debug an inexplicable problem;

Whatever the reason, you can do it.

Here is how you can proceed on Linux.

Set a iptables rule to redirect port 3306 to port 13306 or to port 4040:

sudo iptables -t nat -I PREROUTING \
-s ! 127.0.0.1 -p tcp \
--dport 3306 -j \
REDIRECT --to-ports 13306

Caveat: This will only work if your clients are connecting from a separate machine. On the same server, this rule spares the local IP address 127.0.0.1.

To undo the redirection, repeat the above command with -D instead of -I.

Working for MySQL is COOL!

A new style for MySQL jobs page.
Haven't you heard? MySQL is hiring!


If the adventurous type doesn't appeal to you, you can opt for the quiet home sweet home version, with the beach sweet beach variation. That's what happened during the recent Summer of Code. I know it's a different story, but when I saw the picture of the career climber in the desert I couldn't resist associating it with Sakila typing away in the beach.

Heading to FrOSCon

I mentioned this event a few weeks ago, but it's worth a reminder.

The Free and Open Source Software Conference is held in Sankt Augustin, a cheerful place near Bonn.


Some reasons to attend:

• the organizers are friendly and efficient
• the program is exciting
• the food is good,
• it's full of open source enthusiasts
• I am meeting with a bunch of friends and colleagues

Do you need more? Ah, yes, my session :)
I will present a topic for database administrators, Monitoring and logging a database server.
But there is also Lenz Grimmer with a talk about Opening the doors and windows of the Cathedral, and Susanne Ebrecht, who will bravely cover the PostgreSQL vs. MySQL, or Venus vs. Mars debate.

See you there!

Another step forward for MySQL Proxy

After a few months of documentation uncertainty, MySQL Proxy has finally hit the official manual. The delay between the release and the manual is not a sign of neglect. The documentation engineer had to catch up while the author kept releasing revision after revision (we are now at revision 156. When the Proxy was announced, it was at revision 9). The Proxy is growing, and so is the interest about this feature. A few days ago, an Oracle user was asking for a Proxy-like feature!

And the surprises are not over. More is coming. Stay tuned.

Go Proxy! Go Jan!

How MySQL 5.1 is going to change your life

Are you getting ready for MySQL 5.1? You should. I know that it's taken a long way from alpha to beta, but now it is really close to GA. Really. There is no way it's going to stay beta forever. Very soon someone in the high management will realize that all the outstanding bugs were fixed, and MySQL 5.1 is ready for prime time.
And then, you will have to get used to it. Meaning that there a lot of stuff that is so attractive, that you will want to explore the manual in search of guidance.
Let me give you a preview of what's there for you.

Partitioning

Better start reading some theory on this stuff. If you have performance problems with huge loads of data, this is really what you should be doing. Partitioning is a chunk of pure performance hooked to a database. It's not in any way related to relational theory, and you don't need to redesign your database, but surely you need to rethink it in terms of partitioning.
Rush to read the manual and Robin Schumacher introductory article. If you really want to get the most about partitioning, though, you should check The Art of SQL (Note: I am not affiliated with the author or the publisher. This advice is out of my goodness only)

Row based replication

This is heavy stuff. For demanding application. If you have been dreaming of a more robust replication mechanism for MySQL, here it is.
Row based replication will send to the slave the data, rather than the statement to reproduce it. All edge cases where normal replication leave you in doubt are now handled efficiently by row-based replication. And if you want to get the best of the two worlds, you can still choose the mixed format. Check it out.

Log tables on demand

Get ready for a new experience. Logs whenever you need them, without scheduling a server reboot.
The new logs can materialize in your server in several shapes. You can have them as files, the same as you have seen them in previous versions, or you can have them as CVS tables (which you can convert to MyISAM or to something else), or you can have both at once, tables and files.
And your logs are dynamic. You can tell the server to start and stop logging, to change the log file name, to log on tables and files or only on one of them, you'll have more options than some video games.
And your life will change when you realize that you will need to plan for backups that include the logs. Yes. This is the downside. Get used to it.

Event scheduler

Someone said that the event scheduler is the coolest new feature in MySQL 5.1. Perhaps it was my reaction as well when I saw it for the first time. I can't tell you if it's the best one, but surely it will change your way of working. Say goodbye to OS dependent schedulers. Your database will take care of its own jobs. Setting up events is ridiculously easy. Once you try, you will be hooked forever.

XML functions

To tell you the truth, this is my least favorite feature in 5.1, because for theoretical reasons I am not fond of XML, but I have to admit that it's going to be damn useful, and I will have to get acquainted to it. It will save time and allow for flexible integration schemes with applications that only talk XML.

What else? MySQL 5.1 will change your life, sure. To see the other reasons for my prediction, check the list of wonders for the upcoming version.

Boost your SQL with Proxy loops

By now, everybody knows that I am quite fond of MySQL Proxy and with reason. Using a Proxy you can add features without need of delving into the intricacies of MySQL server code. One of the features that you can create with the Proxy, once you are familiar with its basic architecture (if you still aren't, you may check Getting started with MySQL Proxy) is a loop. So many times I catch myself doing things like $ for N in `seq 1 10` ; do mysql -e "CREATE TABLE t$N (id int)"; done or something like that. Why, oh why there is no FOR command in MySQL syntax?

Some time ago, I created a working solution using stored routines, but it is less than perfect. It requires installation, and the routines are limited to one database, thus requiring an unnecessary amount of detail to make it work.

Proxy loops with a counter.

Enter the Proxy, and the solution is surprisingly slim.
What you need to do is start the proxy with the loop module from MySQL Forge. Then, from your client you can do loops:

mysql> set @x =0;
Query OK, 0 rows affected (0.02 sec)

mysql> for 1 10 select @x := @x + 1 as x;
+------+
| x    |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
|    6 |
|    7 |
|    8 |
|    9 |
|   10 |
+------+
10 rows in set (0.42 sec)

This is the simplest syntax. It requires a command (FOR) a start counter (1) a stop counter (10) and a query (select @x := @x + 1 as x).
The Proxy does the rest, sending the query as many times you required, and collecting the results in practical tabular form. You can actually refer to a counter in the query itself.

mysql> for 1 5 create table t$N (id int);
+--------+--------+---------------+
| inj_id | result | affected rows |
+--------+--------+---------------+
| 1      | 0      | 0             |
| 2      | 0      | 0             |
| 3      | 0      | 0             |
| 4      | 0      | 0             |
| 5      | 0      | 0             |
+--------+--------+---------------+
5 rows in set (0.02 sec)

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t1             |
| t2             |
| t3             |
| t4             |
| t5             |
+----------------+
5 rows in set (0.00 sec)

The $N variables refers to the current counter. The Proxy script will do the change before sending the query to the server. The result is shown in a dataset. A '0' (zero) means no error. When an actual error occurs, the loop is stopped, and the results up to that point are reported.

mysql> drop table t1;
Query OK, 0 rows affected (0.00 sec)

mysql> for 1 5 create table t$N (id int);
+--------+--------+---------------+
| inj_id | result | affected rows |
+--------+--------+---------------+
| 1      | 0      | 0             |
| 2      | -1     | 0             |
+--------+--------+---------------+
2 rows in set (0.01 sec)

mysql> show errors;
+-------+------+---------------------------+
| Level | Code | Message                   |
+-------+------+---------------------------+
| Error | 1050 | Table 't2' already exists |
+-------+------+---------------------------+
1 row in set (0.00 sec)

I removed one table (so the first command in the loop succeds) and when the second query is executed, an error is reported. The loop is immediately interrupted and the result is relayed to the client.

Proxy loops with a list.

Counters are useful, but they are not always what you need. Sometimes, you need to loop though a list. The above mentioned module supports a second syntax, using a list of comma separated items instead of a counter.

FOR user_var (items, in, a, list) your query

Easy to use. Really. Want to create three tables with the same structure but different names? Presto!

mysql> FOR mytable (the_first, the_second, the_third, something_else) CREATE TABLE $mytable (id int);
+--------+--------+---------------+
| inj_id | result | affected rows |
+--------+--------+---------------+
| 1      | 0      | 0             |
| 2      | 0      | 0             |
| 3      | 0      | 0             |
| 4      | 0      | 0             |
+--------+--------+---------------+
4 rows in set (0.05 sec)

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| something_else |
| the_first      |
| the_second     |
| the_third      |
+----------------+
4 rows in set (0.00 sec)

Even if you don't declare a counter, nonetheless you can use one in your query, if needed. Suppose you want to create the tables in such a way that the first one has a CHAR(1) column, the second one a CHAR(2), and so on.
It's a lame example, but you can do it, using the now familiar $N variable.

mysql> FOR mytable (the_first, the_second, the_third, something_else) CREATE TABLE $mytable (name char($N ) );
+--------+--------+---------------+
| inj_id | result | affected rows |
+--------+--------+---------------+
| 1      | 0      | 0             |
| 2      | 0      | 0             |
| 3      | 0      | 0             |
| 4      | 0      | 0             |
+--------+--------+---------------+
4 rows in set (0.05 sec)

mysql> desc the_first;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| name  | char(1) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

mysql> desc the_second;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| name  | char(2) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

As usual, enjoy, and give it a try!

mysqldump unusual error

A friend of mine called me today, asking for advice on a baffling error.
He has just finished upgrading a database server from 4.1.20 to 5.0.45but, when attempting a backup to all databases with mysqldump, he gets a discomforting message:

mysqldump: Got error: 1044:
Access denied for user 'root'@'localhost' to database 'information_schema'
when using LOCK TABLES

Of course, the error is doubly strange.

• First, because mysqldump is not supposed to attempt dumping the information schema. I know for sure, since I had to write a special script to dump the I_S when I really needed to export its data.
• Second, because there was actually a bug affecting this behavior, but it was fixed over one year ago.

Looking at the bug report, though, I saw that someone was complaining about this bug again recently.
I don't believe without action, so I rapidly installed a 5.0.45 and I tried to repeat the offending behavior. No luck. Everything worked as expected.
Then it dawned on me that perhaps he was not using the right mysqldump. I asked my friend to report the version of the dump, and indeed, it was a version that comes with MySQL 4.1.
Apparently, an old version of the client tools were still stuck in the OS execution path, before the directory where the new ones were installed.
A couple of minutes later, having cleaned the installation, all went well.
Lesson learned: before crying "bug", try "--version"!

Summer of Code pleasures

As a professional tester, I have a dream about a tool that will let me use my favorite SQL manager, and at the same time create tests ready to be plugged to the regression test suite.
I have been dreaming and planning about it, and finally the magic tool is shaping up.
I am mentoring a Summer of Code project, assigned to Charlie Cahoon. After a long preparatory work and much planning, the MySQL test creator is finally out!
Initially, it was planned as a separated tool, a replacement for the MySQL command line. The idea is that you write queries and eye the results, while the tool in background is writing a polished test script. That would have been a good tool, multi platform, easy to use, but limited to the command line.
Then the MySQL Proxy came along, and we decided to use it as a backend. Thus the tool, instead of being written in C++, it ended up in Lua. Kudos to Charlie for learning the language very quickly and for coding it.
The tool is not ready yet. It has just the basic features, but it has now reached the stage when it can actually produce a simple test script+result pair.
For example, This is what I would type to check that the CREATE, INSERT, and SELECT statements are supported (not exhaustive test, of course!)

mysql> start;  # This is a macro from the magic tool
Query OK, 0 rows affected (0.00 sec)

mysql> drop table if exists t1;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> create table t1 (id int, c char(10));
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t1 values (1,'a'), (2,'b');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from t1;
+------+------+
| id   | c    |
+------+------+
|    1 | a    |
|    2 | b    |
+------+------+
2 rows in set (0.01 sec)

mysql> stop; # another macro. The tool stops recording now
Query OK, 0 rows affected (0.01 sec)

mysql> exit

What I see on the screen is not what I need to get in a test script. If I had found a bug here and I wanted to submit it, I would have to do some cut-and-pasting and clean-up. Instead, the mysql-test-creator is doing that for me.

$ cat creator.test
--disable_warnings
DROP TABLES if exists t1;
--enable_warnings
create table t1 (id int, c char(10));
insert into t1 values (1), (2);
insert into t1 values (1,'a'), (2,'b');
select * from t1;

$ cat creator.result
DROP TABLES if exists t1;
create table t1 (id int, c char(10));
insert into t1 values (1,'a'), (2,'b');
select * from t1;
id c
1 a
2 b

Isn't it sweet?
Bravo Charlie!

More is coming. The tool will support multiple sessions at once, with the creation of a unified test script from several sessions. Stay tuned!

Tell the world about your first time impression - Usability Reports

MySQL, like most software companies, has a complex organization to deal with the creation and improvement of its products.
There is a well oiled machinery that evaluates the needs and decides where to invest resources to create new products or to expand or change existing ones.
Ultimately, what affects the decision is the users satisfaction.
However, funnily as it may sound, the best organized activity in our company is bugs processing i.e. the one dealing with users dissatisfaction.
I would like to see more positive input from the users, and thus I put together the guidelines for a Usability Report.
What is is?
In short, it is the account of a user first impression with a product or a feature. If you decide today to start testing, say, the Falcon engine, you could write a usability report to convey your experience to MySQL.
The usability report should be divided into sections, to make it easier for you to write and easy to read for the ones evaluating community feedback and taking decisions.

• product identification
  
• Expectations
• Clarity of documentation
• Ease of use
• Real world usage
• Bugs
• Missing pieces
• Level of satisfaction
• (optional) Test units

You can see an example in the Forge. It's a report that I wrote in August 2006, a month or so before joining MySQL. You can use my first experience with logs on demand as an example of how to write a report.
Want to have your voice heard? Visit MySQL Forge, and submit your first Usability Report.

Getting started with MySQL Proxy

Did you notice that there is a new component among MySQL products? No? Perhaps you have been on vacation, then.
MySQL Proxy is an exciting tool for anyone willing to get new features now without waiting for new server major releases.
Using the Proxy you can filter queries, create new commands, create customized logs, play with the operating system from any database client, and much more.
Interested? Read Getting started with MySQL Proxy

Finding Falcon hidden bugs - with a little help from my shell

There is a song that keeps popping on my mind when I test something difficult. Usually, when I can't get the result I am seeking with normal operations, and I have to resort to some trick, I hear Joe Cocker singing With a little help from my friends. My best friends when I test are bash, vim, and perl.
Today, I was testing Falcon on my Intel based MacBook. The last Falcon release does not compile on Macs, but it has been recently patched, and today with my delight it built smoothly.
Having got the binaries, I ran the test suite, because that's the fastest way of finding out if something is broken. Soon enough, something nasty popped up. Test "falcon_bug_29040" failed with timeout. Thus, I switched to full bug finding mode, and ran the test again.
Odd. When run alone, it succeeds.
I restart the test suite. Again, it fails, but it is executed after some 40 different tests. Apparently, there is a conflict. Either a previous test is not cleaning up after itself, or there is yet another bug to be filed.
Then the task is: how do I know which of the previous tests make it fail?
The solution is to run the tests before "falcon_bug_28040" one at the time, with the suspect one immediately after. When I get a failure, I know who the culprit is.
With a little help from my shell, the task is easy:

for T in t/falcon_bug_2[234567]*.test ; \
  do \ 
    TEST=`basename $T .test` ; \
    echo $T $TEST ; 
    ./mtr --skip-ndb --skip-im $TEST falcon_bug_28040 ; \
done

The tests before the one under examination are all falcon_bug_XXXXX, where XXXX ranges from 22089 to 27997. So I ask the shell to single out the tests in that range. For each one, I get the base name (without extension), and I pass it to the test runner. Total time to find the culprit: three minutes.
It took me much more to submit the bug report and to write this account of the facts!

Speaking at FrOSCon - Monitoring and logging techniques

If you happen to be in Northern Germany at the end of August, I recommend a visit to Sankt Augustin, a charming city near Bonn.
Apart from the friendly atmosphere and excellent beverages, Sankt Augustin hosts the second edition of FrOSCon, the Free and Open Source Software Conference, organized by a group of very dynamic and efficient enthusiasts.



I will present a topic for database administrators, Monitoring and logging a database server.

And of course I will meet a bunch of friends there. Someone I know very well, like Lenz Grimmer, who will speak about Opening the doors of the Cathedral, and Zak Greant, whose session about the age of literate machines sadly I won't attend because it coincides with mine.
And then there are those who I know only by email, and I will gladly meet in person, like Susanne Ebrecht, who will bravely cover the PostgreSQL vs. MySQL, or Venus vs. Mars debate.
The list is long, and the conference lasts only two days, so I will try to make the best of it.
See you there!

Bug processing disclosure - The busy bees of MySQL AB

Ever wondered what happens after you submit a bug report to MySQL?
Puzzled at the cryptic messages that tell you about your report going from verified to in process?
Who on earth are those Valeriy, Sinisa, Victoria, Miguel, Sveta, Tonci who comment on your report?
Wonder no more.

MySQL bug processing explained disclose in tiny detail who are the busy bees in MySQL hive and how do they get from the pollen of your bug report to the honey of a bug fix.

Building MySQL Proxy on Mac OS X

Version 0.5.0 of MySQL Proxy was released a week ago, and in the meantime there have been 25 revisions.
If you want to try the latest version in your box, you can get the sources from the svn repository and build it yourself.

svn co http://svn.mysql.com/svnpublic/mysql-proxy/ mysql-proxy

Then, you can build and install this way.

./autogen.sh && ./configure && make && make install

That works beautifully on my Linux desktop.

So far, the good news. The bad ones is that on my Mac OS X laptop, things are not so smooth.
First, aclocal complained about missing macros. Jan was online, and he helped me fix the problem with an environment variable.
Then ./configure could not find the right Lua settings. More options.
Again, ./configure could not find libevent.
In the end, I managed to build the coveted proxy with the following instructions, which I saved in a shell script, because I am going to need it quite often.
Here it is, in case someone gets stuck on the same problem.

export ACLOCAL_FLAGS="-I /sw/share/aclocal/"
./autogen.sh && ./configure LUA_CFLAGS="" \
   LUA_LDFLAGS= LUA_LIBS="-llua" \
   CPPFLAGS="-I/opt/local/include/" \
   LDFLAGS="-L/opt/local/lib/"  && make && make install

Update 2007-07-02: Version 0.5.1 was released today. Now that's a fast development cycle!

MySQL as universal server

With all the discussion going on about MySQL Proxy, we may forget that there are alternatives.
Today in the MySQL Dev Zone there is an article about a different proxy. It's more than that, actually. It is a Perl Module implementing the MySQL client/server protocol.
With this tool, you can emulate some of MySQL Proxy features, and you can do something more. For example, you can use Federated tables with non-MySQL database servers. The article features an example where a table from SQLite and a table from PostgreSQL are queried as if they were normal MySQL tables.

Your first macros with MySQL Proxy

You may have noticed the excitement about MySQL Proxy. But perhaps you failed to realize what you can do with it.
Here's a simple tutorial that will guide you through your first Proxy experience. You will be able to use macros with the standard mysql client.

Assuming that you are working on the box where your MySQL server is, do the following:

1. Download and unpack MySQL Proxy
2. download the query rewriting tutorial and save it as rewrite.lua
3. start the proxy
   /path/to/sbin/mysql-proxy --proxy-lua-script=rewrite.lua --proxy-profiling
4. from another terminal, fire the mysql client
   mysql -u USERNAME -pPASSWORD -h 127.0.0.1 -P 4040

Now you can use your client as usual, with a few additions. The rewrite.lua script implements three macros (cd, ls, who, corresponding respectively to USE, SHOW FULL TABLES, and SHOW PROCESSLIST).

mysql> cd test;
Query OK, 0 rows affected (0.00 sec)

mysql> select schema();
+----------+
| schema() |
+----------+
| test     |
+----------+
1 row in set (0.00 sec)

mysql> cd mysql;
Query OK, 0 rows affected (0.00 sec)

mysql> select schema();
+----------+
| schema() |
+----------+
| mysql    |
+----------+
1 row in set (0.00 sec)

Look at that! We send a macro (cd test) to the server. The proxy catches it, and turns it into "use test". The server executes it, unaware of the manipulation in between. Let's try the others:

mysql> ls mysql;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| func                      |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| host                      |
| proc                      |
| procs_priv                |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
17 rows in set (0.00 sec)

mysql> who;
+----+-------------+-----------------+-------+---------+------+-------+------------------+
| Id | User        | Host            | db    | Command | Time | State | Info             |
+----+-------------+-----------------+-------+---------+------+-------+------------------+
|  4 | datacharmer | localhost       | bugs  | Sleep   | 1522 |       | NULL             |
| 11 | gmax        | localhost:50630 | mysql | Query   |    0 | NULL  | SHOW PROCESSLIST |
+----+-------------+-----------------+-------+---------+------+-------+------------------+
2 rows in set (0.00 sec)

And now we add our own macro to the list. Stop the proxy. Edit rewrite.lua, and just before the line saying

elseif command == "who" then

add these three lines, implementing a info macro, which corresponds to "SELECT USER(), NOW()":

                elseif command == "info" then
                       proxy.queries:append(1, string.char(proxy.COM_QUERY) .. "SELECT USER(), NOW()" )
                       return proxy.PROXY_SEND_QUERY

Restart the proxy, and try your new macro:

mysql> info;
+----------------+---------------------+
| USER()         | NOW()               |
+----------------+---------------------+
| gmax@localhost | 2007-06-27 10:24:00 |
+----------------+---------------------+
1 row in set (0.00 sec)

Isn't it cool? And that's just the beginning.

MySQL Proxy - An excellent excuse to learn a new language

If you are as curious as I am about technology, you would have been intrigued when the MySQL proxy entered the radar. So I followed this promising jewel from its first inception as source only (and for internal distribution) until its release with a full series of binaries.

The recent announcement has made it official. MySQL Proxy is a full fledged supported product, and it's ready to use.
You just have to get the binaries and use it.
If you feel like experimenting (and there is no reason to get the proxy if you aren't) you can have a look at the sample lua scripts available on the Forge and play with them. You may notice that there is one snippet that I created. If you are thinking of calling me for lua lessons, think again. When I wrote that example, my entire production with lua amounted to three scripts, and the total length of my lua experience could be measured in hours.
Having used at least a dozen languages (including the usual suspects Pascal, C, C++, and Perl, but also things like Sather), a new scripting language does not scare me. I believe that I am going to see more of this lua, and I believe that lots of MySQL users are going to become proficient lua speakers in the near future.
Good job, Jan!

Users, give the proxy a try. And if you can't figure out what to do with it, stay tuned. I have a couple of article on this subject, and not only about this proxy, coming soon.

Test suites for the masses

Overview

Test suites are hard, but your business needs to have one.
They are hard because modern applications are complex.
Technology can help you. There are tools that can simplify the task of creating a thorough test suite.

Does your main business have a regression test?

The likely answers to the above questions are:

• Yes. - Good chap. Keep up the good work. You may stop reading, but just out of curiosity, read on.
  
• No. I don't need one. - You may stop reading. Most likely your business is already doomed. :)
• No. I don't have time (don't know how) to make one. - Keep reading. There is something for you.

What's a regression test? Is a useful watchdog that tells you if your software is working the way it was intended to.
If you don't have one, you have no quick and reliable way of telling if your application is safe.
If you think that you don't need a regression test suite, either you have found the formula of making perfect software, or your optimism is way off mark.

Tests are hard

If you have a test suite, you know that it requires hard work, dedication, cunning ways of thinking, technical abilities.
If your business includes a MySQL database, you may consider using its specific test framework, which introduces yet another level of difficulty.
MySQL testing framework is designed to allow testing any database scheme (stand alone, replicated, clusters) with just one box, at the price of some language addition that you would need to learn.
Writing your own regression test that covers your application means replaying the data structure and the queries, to make sure that, if you alter the working environment, your application continues working as required.

The most likely scenario occurs when you need to upgrade. Your current server has a bug that was just fixed in a more recent one. You would like to upgrade, but before doing that you would like to be sure that the new environment is capable of running your queries without side effects.
A regression test would solve the problem. You set up a temporary server, install the upgraded software and run the test suite. If you don't get errors, you may confidently upgrade. It depends on how thorough is your test, of course. The more you cover, the more you can trust it.
If you don't have a regression test and you need to upgrade, you are in trouble. If there are inconsistencies between your application and the new version, you will find out when a user complains about a failure. Which is not the most desirable course of action.

Understanding the problem

Why making a test suite for an application is so hard? Mostly because you don't usually have a list of all queries running against your server. Even if you planned a modular application and all your database calls are grouped in one easy accessible part of your code, that won't solve your problem. Modern applications don't use static queries. Most queries are created on the fly by your application server, twisting a template and adding parameters from users input.
And even if your templates are really well planned, so that they leave nothing to imagination, you will have trouble figuring out what happens when many requests access your database concurrently.
Smarter applications can log all database requests and leave a trail that you can use to create your test. But more complex systems count more than one application, and taking trace of all their queries is a real headache.

Making tests easier

Fortunately, there is a central place where all queries go. Your server.
Unfortunately, the server does not create a test case for you. It just records all calls in the general log, and it that is not suitable for further consumption.
Here comes the technology I mentioned earlier. You can make a test script out of your general log.

1. activate the general log;
2. Download the test maker;
3. Inspect the general log and identify the likely period when the most important queries occur;
4. tell the test maker to read the above traffic (which you can identify by line number or by timestamp)
5. edit the resulting test and see if covers your needs.
   

The test maker is a collection of two tools. One that can get a snapshot of your data (like mysqldump, but with a LIMIT clause, so that you can take only a sample of your data) and the test maker itself, which reads the general log and creates a script. You can tune this tool with several options.

 Log Analyzer and test maker,  version 1.0.2 [2007-06-10]
 (C) 2007 Giuseppe Maxia, MySQL AB
 Syntax: ./testing_tools/test_maker.pl [options] log_file test_file
 --add_disable_warnings|w        Add disable warnings before DROP commands. (default: 0))
 --from_timestamp|t = name       Starts analyzing from given timestamp. (default: undefined))
 --to_timestamp|T = name         Stops analyzing at given timestamp. (default: undefined))
 --from_line|l = number          Starts analyzing at given line. (default: first))
 --to_line|L = number            Stops analyzing at given line. (default: last))
 --from_statement|s = name       Starts analyzing at given statement. (default: first))
 --to_statement|S = name         Stops analyzing at given statement. (default: last))
 --dbs = name                    Comma separate list of databases to parse. (default: all))
 --users = name                  Comma separate list of users to parse. (default: all))
 --connections = name            Comma separate list of connection IDs to parse. (default: all))
 --verbose                       Adds more info to the test . (default: 0 ))
 --help                          Display this help . (default: 0 ))

As you can see from the options, you can filter the log by several combinations of connection ID, users list, timestamps, line numbers.
The resulting script is suitable for the MySQL test framework.

Advantages

The test maker is not a panacea, but it helps reducing your test suite development time. Running this tool you will get a passable starting test, which you can then refine to make it closer to your needs.
The main advantage is that you can have a set of instructions that were run against your production server, and you can replay against a testing server when you need to upgrade.
If some features of MySQL 5.1 look appealing and you plan to upgrade, then a test suite is the best way of making sure that the switch will be painless.

More than that, once you have a test suite, consider joining the Community Testing and Benchmarking Program, a project to share test suites from the Community, so that your test case becomes part of MySQL AB suite. Thus, you won't be alone with your upgrade problems. If there are any regression failures, they will be addressed before the next version is released, for the mutual benefit of company and users.

Known issues

There are problems, of course.
The general log is not turned on by default. To switch it on, you need to restart the server, and to switch it off you will do that again (until you upgrade to MySQL 5.1, which has logs on demand).
Moreover, the general log can become huge, so you need additional maintenance, to avoid filling the whole disk with logs.
Furthermore, the general log will record everything sent to the server, even wrong queries. While this is desirable for a test case, because testing failures is as important as testing compliance, you will need to adjust manually the test script, adding "--error" directives.
Again, the test maker records only the test script, but not the result, which you will need to create using the testing framework.
All in all, having a tool writing a big chunk of the test script is much better than doing it all manually. So even if this is not a complete solution, it's a hell of a good start.
Comments welcome.

Use 5.1 partitions in production - Today!

MySQL 5.1, the next major version, has a bunch of juicy features that many people would like to use in production, if only it were already GA. Partitioning for example, is one of those features that all users want to get their hands on. It is about performance. Partitioning can reduce response times dramatically, if applied correctly. I don't need to convince you of this. You can read one of the several articles about the technicalities of partitions (there is one piece about the performance of partitioned archive tables in this very blog).

The only problem is that MySQL 5.1 is still in beta. The number of outstanding bugs is shrinking by the day, and the number of reported bugs is receding, but nonetheless, it's not a GA release, and therefore the conscientious DBA is (justly) reluctant at the idea of using it in production.
Those partitions, though, are really tempting. Perhaps we can play some trick to use them, while keeping our data safe.
There are ways where you could use MySQL 5.1 in production, especially partitions, without endangering your valuable data. The easiest one is with replication.

MySQL replication is a cheap, reliable, fast way of synchronizing data among servers and balancing the query load, if you are willing to split your application logic so that you write on one server (the master) and read from another one, or several ones (the slave).

One nice feature of MySQL replication is that it can work across versions, as long as the most recent one is used in the slave. So you can set your real production server as the master, running MySQL 5.0, the legitimate GA release, while the slave will run MySQL 5.1.



The steps to achieve this feat are simple:

• make sure that your master is using a binary log and has a unique server ID;
  
• create a user with REPLICATION SLAVE privileges;
• on the slave, install MySQL 5.1, with a different server ID, but don't start the replication yet;
• dump the data from master to slave, using the mysqldump options --master-data=1 and --single-transaction;
• On the slave, Alter the structure of the tables that you want to partition;
  
• start the slave.
  

Now you can instruct your application to send expensive queries to the slave, instead of the master. Now your most demanding SELECT statements can take advantage of partitioning, while your data is safely held in the GA master.

Think of the advantages:

• You will speed up some of your expensive queries. (Beware. It is not always easy. You need to check your table design, but in the end, it works spectacularly);
• If you find a bug in 5.1, you can help the development without risking the integrity of your data, which is still safe inside the master.
  

If you still have doubts, I'll let you in a little secret. At MySQL, at least two production databases have been running on 5.1 for one year already. We trust it, even though we can't officially tell you to do the same. But I can recommend you the little replication trick that will let you use the new features with no risks.