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One problem with MySQL Cluster we are starting to see quite often is to do with the current generation of Xeon processors.  This post outlines the problem and how to avoid it.

With the Nehalem based Intel Xeons (and also in some older AMD CPUs) they add a technology called NUMA (Non-Uniform Memory Access).  This basically gives each CPU its own bank of memory instead of all CPUs accessing all the memory.  For many applications this means much faster memory access. You should be able to see if NUMA is on by looking for it in dmesg.

So why is this a bad thing?

MySQL Cluster data nodes typically require a large portion of the memory, this means very often that one CPU will need to access the memory from another other CPU.  This in general is quite slow, on a busy cluster we have seen this access take 100ms - 500ms!  MySQL Cluster is real-time and is not a happy bunny when there are things stopping it becoming real-time.  Therefore typically watchdog timeouts are very regular in NUMA based systems.

So, how can this be improved?

For starters NUMA is easy to turn off, simply add the kernel boot option numa=off.  We have also observed that later Linux kernels (around 2.6.30) have improved the scheduler for NUMA and appear to be friendlier to MySQL Cluster.  But I would personally recommend turning it off even with newer kernels.

What else can cause problems?

We do not yet have as much data on this, but it is also believed that dynamic CPU clocking can also cause similar issues.  If the data node is not busy the CPU is clocked down which then causes timing issues for cluster.  I would recommend setting the CPU to full performance settings where possible.

Edit: Mat Keep has confirmed that dynamic CPU clocking certainly causes performance issues in the comments.

Hyper-threading can also be a killer.  If you have a 4 core CPU with hyper-threading it shows as 8 cores, but since these are not full cores setting MaxNoOfExectionThreads=8 can cause a lot of contention.  In most cases you do not need to turn hyper-threading off but do not try to give the CPUs more workload than they can handle. 

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If you have tried Quick start guides: MySQL cluster in 10 minutes, you may have realized that it is really quick and easy. However, it leaves some typing to be done. Users of MySQL Sandbox have a horror of repetitive typing, and this got me thinking. "Could I integrate MySQL Sandbox and Cluster?" The answer was: "Sure." But then I started thinking of all the minor and major changes that I wanted to do to the Sandbox and have delayed for too long. What I need, is a radical refactoring. And then I remembered that it has been almost two years since I learned a new programming language and that perhaps I could expand my horizons and the Sandbox architecture at once.

Thus, thanks to an irresistible offer from O'reilly about ebooks, last week I bought both Learning Python, fourth edition and Programming Python, Third edition.
During the week end I produced my first tool: a Python script that installs and starts a small cluster, following the instructions given in the MySQL Cluster quick start guides. The script unpacks the cluster tarball, installs a server sandbox from it, then starts the cluster nodes and the MySQL server, and then it monitors the cluster until all the nodes are connected before finally testing the server.
Here is a sample run:

$ make_cluster.py ~/Downloads/mysql-cluster-gpl-7.1.4b-osx10.6-x86_64.tar.gz

++ tar -xzf ~/Downloads/mysql-cluster-gpl-7.1.4b-osx10.6-x86_64.tar.gz

++ low_level_make_sandbox --basedir=$HOME/python/mysql-cluster-gpl-7.1.4b-osx10.6-x86_64 --sandbox_directory=mcluster --install_version=5.1 --sandbox_port=5144 --no_ver_after_name --no_run --force --my_clause=log-error=msandbox.err --my_clause=ndbcluster 
    The MySQL Sandbox,  version 3.0.12
    (C) 2006-2010 Giuseppe Maxia
installing with the following parameters:
upper_directory                = $HOME/sandboxes
sandbox_directory              = mcluster
sandbox_port                   = 5144
check_port                     = 
no_check_port                  = 
datadir_from                   = script
install_version                = 5.1
basedir                        = $HOME/python/mysql-cluster-gpl-7.1.4b-osx10.6-x86_64
tmpdir                         = 
my_file                        = 
operating_system_user          = gmax
db_user                        = msandbox
db_password                    = msandbox
my_clause                      = log-error=msandbox.err ; ndbcluster
prompt_prefix                  = mysql
prompt_body                    =  [\h] {\u} (\d) > 
force                          = 1
no_ver_after_name              = 1
verbose                        = 
load_grants                    = 1
no_load_grants                 = 
no_run                         = 1
no_show                        = 
loading grants
.. sandbox server started
stopping server
Your sandbox server was installed in $HOME/sandboxes/mcluster

++ mysql-cluster-gpl-7.1.4b-osx10.6-x86_64/bin/ndb_mgmd -f $HOME/sandboxes/mcluster/my_cluster/conf/config.ini --initial --configdir=$HOME/sandboxes/mcluster/my_cluster/conf/
2010-06-28 21:29:57 [MgmtSrvr] INFO     -- NDB Cluster Management Server. mysql-5.1.44 ndb-7.1.4b
2010-06-28 21:29:57 [MgmtSrvr] INFO     -- Reading cluster configuration from '$HOME/sandboxes/mcluster/my_cluster/conf/config.ini'

++ mysql-cluster-gpl-7.1.4b-osx10.6-x86_64/bin/ndbd -c localhost:1186
2010-06-28 21:29:57 [ndbd] INFO     -- Configuration fetched from 'localhost:1186', generation: 1

++ mysql-cluster-gpl-7.1.4b-osx10.6-x86_64/bin/ndbd -c localhost:1186
2010-06-28 21:29:57 [ndbd] INFO     -- Configuration fetched from 'localhost:1186', generation: 1

++ mysql-cluster-gpl-7.1.4b-osx10.6-x86_64/bin/ndb_mgm -e show
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=3 (not connected, accepting connect from localhost)
id=4 (not connected, accepting connect from localhost)

[ndb_mgmd(MGM)] 1 node(s)
id=1 @localhost  (mysql-5.1.44 ndb-7.1.4)

[mysqld(API)] 1 node(s)
id=50 (not connected, accepting connect from any host)


++ $HOME/sandboxes/mcluster/clear

++ $HOME/sandboxes/mcluster/start
... sandbox server started
Please wait. Giving the cluster time to catch up
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=3 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, starting, Nodegroup: 0, Master)
id=4 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, starting, Nodegroup: 0)

[ndb_mgmd(MGM)] 1 node(s)
id=1 @localhost  (mysql-5.1.44 ndb-7.1.4)

[mysqld(API)] 1 node(s)
id=50 (not connected, accepting connect from any host)


It may take up to 2 minutes to initialize ... ( 0 )
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=3 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, starting, Nodegroup: 0, Master)
id=4 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, starting, Nodegroup: 0)

[ndb_mgmd(MGM)] 1 node(s)
id=1 @localhost  (mysql-5.1.44 ndb-7.1.4)

[mysqld(API)] 1 node(s)
id=50 (not connected, accepting connect from any host)


It may take up to 2 minutes to initialize ... ( 5 )
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=3 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, starting, Nodegroup: 0, Master)
id=4 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, starting, Nodegroup: 0)

[ndb_mgmd(MGM)] 1 node(s)
id=1 @localhost  (mysql-5.1.44 ndb-7.1.4)

[mysqld(API)] 1 node(s)
id=50 (not connected, accepting connect from any host)

[...]

It may take up to 2 minutes to initialize ... ( 100 )
Connected to Management Server at: localhost:1186
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=3 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, Nodegroup: 0, Master)
id=4 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4, Nodegroup: 0)

[ndb_mgmd(MGM)] 1 node(s)
id=1 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4)

[mysqld(API)] 1 node(s)
id=50 @127.0.0.1  (mysql-5.1.44 ndb-7.1.4)


++ $HOME/sandboxes/mcluster/use -vvv -e "create table test.t1(i int not null primary key)engine=ndb"
--------------
create table test.t1(i int not null primary key)engine=ndb
--------------
Query OK, 0 rows affected (0.45 sec)

++ $HOME/sandboxes/mcluster/use -vvv -e "show create table test.t1\G"
--------------
show create table test.t1
--------------

*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `i` int(11) NOT NULL,
  PRIMARY KEY (`i`)
) ENGINE=ndbcluster DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

to shut down the cluster, type:
$HOME/python/mysql-cluster-gpl-7.1.4b-osx10.6-x86_64/bin/ndb_mgm -e shutdown

It works! Ans this is a good start to make me feel confident with Python, which I will use to develop MySQL Sandbox version 4. This cluster snippet will probably be made from scratch once the new architecture is in place. For now, it was enough to get the feeling of the language.
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Scared of MySQL Cluster? Don't be. You may want to try the quick start guides that are available in the Cluster downloads page. These guides are a step-by-step instructions set to create a simple cluster in one host. Following the instructions, you will be able to shape up all the cluster components in 10 minutes or less. This will be far from production ready, of course, but it shows that cluster is not rocket science, and anyone can get started with it with a minimal time investment.

I tried the Linux instructions on my Mac, and it worked without need for any changes. Things may be different when you deploy a real set of servers on separate hosts, but it's a good start.
If I compare this guide with my first experience with MySQL Cluster in 2004, usability and stability have increased enormously.
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The MySQL Cluster daemon for MySQL Cluster (ndbd and ndb_mgmd) doesn't by themselves yet let them run as a service (apparently ndb_mgmd does, but I haven't seen it documented anywhere on how to do that). But there are ways to fix this, using some simple Windows tools and some registry hacking.

What you need to find is the Windows Resource Kit from some version of Windows that includes instsrv.exe and srvany.exe. It is not too picky with the actual version of Windows you run it seems, I used the Windows NT 32-bit versions of these on a 64-bit Windows 7 box, and it works just fine.

These two programs are simple and are easy to use:

• instsrv allows you to install a service, it's real simple, just run the program and it will show the options (and these are few).
• srvany allows you to run any odd program, that is not intended run as a service, do do this anyway.

Now, Google a bit and download these two puppies and open a DOS Window and change directory to where you installed these guys. Now we are realy to install three services (1 for the mgm and two datanodes), so they will run the srvany program:
F:>ResKit> instsrv mgm1 F:\ResKit\srvany.exe
F:>ResKit> instsrv ndbd1 F:\ResKit\srvany.exe
F:>ResKit> instsrv ndbd2 F:\ResKit\srvany.exe

These three services are rather boring now, they do not do anything, really. To fix this, open the registry editor (regedit) and open:
HKEY_LOCAL_MACHINE\System\CurrentControlset\services\mgm1
Now, we need to define what srvany.exe should run. In the key above, create a new key called Parameters. In this key then, create two values:

• Application - The full path to the program srvany should run.
• AppParameters - The parameters to pass to the program srvany will run.

In my case, I set these to, for the mgm service:
Application: F:\MySQL714\bin\ndb_mgmd.exe
AppParams: --config-file=F:\MySQL714\mgm1\config.ini --configdir=F:\MySQL714\mgm1

I think you see where I'm going with this, but just to be sure, this is what I set for the ndbd1 service:
Application: F:\MySQL714\bin\ndbd.exe
AppParams: --ndb_connectstring=nodeid=2;host=localhost:1186

And that's it, folks! Well, one more thing I guess, we want to install the MySQL Server as a serive also, but this knows how to install itself as a service and can also run nicely as a service, so this is easy:
F:\ResKit>F:\MySQL714\bin\mysqld --install MySQL714 --defaults-file=F:\MySQL714\my.ini

Make sure that the ini-file for the MySQL server is configured to access the cluster we just set up, and to have the ndbcluster engine enabled (for some reason, the latter is not enabled by default). Do this by editing the my.ini file used by the server (and referenced above) and add the following two lines to the [mysqld] section:
ndb-connectstring=host=localhost:1186
ndbcluster

Now we have created and configured a bunch of services for a MySQL Cluster setup, and to try it out, lets start them using the NET command line program (the SC command may also be used):
F:\ResKit> net start mgm1
F:\ResKit> net start ndbd1
F:\ResKit> net start ndbd2
F:\ResKit> net start MySQL714

Have fun! And just a word of caution: Although this works just fine for testing, note that shutdown of the ndbd and mgm services isnt really graceful here, so this is just for fun and testing. Also, ndbd and ndb_mgmd will sure be possible to run as a Windows service in their own right, in some future version of MySQL Cluster.

/Karlsson
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This post explains how to disable Arbitration when using MySQL Cluster. It gives a case where this could be useful.

First, a piece of advice: you do not want to run MySQL Cluster with arbitration disabled. But if you must, e.g. because of an oversight in your implementation, you can.
Arbitration is very important in MySQL Cluster. It makes sure you don't end up with a Split Brain situation: 2 halves working independently, continuing changing data, making it impossible for them to work together later on.

However, Arbitration comes with a price: you need an extra machine. "Sure, what's the big deal?". It's not that easy when you lack the money, or more problematic, when you lack the real-estate in your rack.

Everyone running MySQL Cluster should know that you should not run the ndb_mgmd on the same machines on which the data node processes, ndbd or ndbmtd, are running. The Management Nodes need to be on a separate machine so it can act as an Arbitrator.

Here's an example why: If you have two hosts A and B and both are running a management and data node process. Host A's ndb_mgmd is currently the Arbitrator. Now unplug host A *BANG*: one data node and the arbitrator down. The other data node on Host B notices this, and tries to figure out if it can continue. So it checks if it can reach the Arbitrator: but it's gone as well! So, the data node on host B goes faithfully down. This all happens in a few seconds, there is no time to elect a new Arbitrator. "Cluster's dead, Jim".

What if you can't get a 3rd machine? There's an option for that.. Data nodes can before configured setting Arbitration to WaitExternal. This means you will have to develop your own arbitration application or script. How cool is that? Well, it might be cool, but it's a pain in the butt.

[ndbd default]
Arbitration = WaitExternal
ArbitrationTimeout = 3

What happens with our 2 host setup with above changes: When Host A, which has the Arbitrator, goes down, the data node on Host B will wait for 3 seconds, i.e. ArbitrationTimeout. It will block all incoming transactions, refusing changes. An application, the External Arbitrator, running on Host B (actually on all hosts running MySQL Cluster proceses) has 3 seconds to figure out whether Host B can continue running it's ndbd process(es), or not. In this case, it should find out that Host A is down and that Host B should continue keeping the data available.

"Ah, easy! Problem solved!", you might joyfully exclaim. No, it isn't. It's more complicated than that. What happens when Host A doesn't go down, but both hosts can't see each other due to a network issue between them? Both External Arbitrators would figure out that they need to continue: you end up again with a split brain. So you still need someway to handle that.

At this point, I would like to say: "Goodluck!". Every situation is going to be different. Everyone will have his own External Arbitrator requirements or ways to check if a host or blade chassis is up or not. It's a great option, and it puts you more in control of your MySQL Cluster, but it adds a lot of complexity.

So, my advice: revise and correct your MySQL Cluster setup when you think you need to disable Arbitration.

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Last week I was struggling to find an easy way to simulate a troubled Data Node (ndbd process) using MySQL Cluster. It's as simple as pancackes: using the kill command!

To freeze a process you just need to kill the process using the SIGSTOP signal. To let the processes continue, use SIGCONT. Here's an example shell script showing how you would use these two signals on a data node:

 # 2010-05-03 08:11:46 [ndbd] INFO     -- Angel pid: 542 ndb pid: 543
 NDBDPID=`grep 'Angel pid' ndb_3_out.log | tail -n1 | awk '{ print $11 }'`
 kill -STOP $NDBDPID
 sleep 10
 kill -CONT $NDBDPID

I'm using the out-log because the file ndb_3.pid contains only the PID of the Angle process. The sleep command is something variable which you can set as low or as high as you want.

In the above example the script sleeps long enough for data node to fail with an Arbitration Error. If you would set options HeartbeatIntervalDbDb and TimeBetweenWatchDogCheck to a lower value than the default, you would only be able to sleep for a few seconds. The result:

 [MgmtSrvr] WARNING  -- Node 2: Node 3 missed heartbeat 2
 [MgmtSrvr] WARNING  -- Node 2: Node 3 missed heartbeat 3
 [MgmtSrvr] ALERT    -- Node 1: Node 3 Disconnected
 [MgmtSrvr] ALERT    -- Node 1: Node 3 Disconnected
 [MgmtSrvr] WARNING  -- Node 2: Node 3 missed heartbeat 4
 [MgmtSrvr] ALERT    -- Node 2: Node 3 declared dead due to missed heartbeat
 [MgmtSrvr] INFO     -- Node 2: Communication to Node 3 closed
 [MgmtSrvr] ALERT    -- Node 2: Network partitioning - arbitration required
 [MgmtSrvr] INFO     -- Node 2: President restarts arbitration thread [state=7]
 [MgmtSrvr] ALERT    -- Node 2: Arbitration won - positive reply from node 1
 [MgmtSrvr] ALERT    -- Node 2: Node 3 Disconnected
 [MgmtSrvr] INFO     -- Node 2: Started arbitrator node 1 [ticket=019b00025cc8aad8]
 [MgmtSrvr] ALERT    -- Node 3: Forced node shutdown completed. 
  Caused by error 2305:  'Node lost connection to other nodes and can not
  form a unpartitioned cluster, please investigate if there are error(s)
  on other node(s)(Arbitration error). Temporary error, restart node'.

How is this useful? Well, for simulating a data node which is having problems while having load for example. Maybe you would like to see what happens if you tune the WatchDog or Hearbeat parameters. Or maybe you want to give a demonstration to your management without going through hassel of overloading a disk or CPU or pulling network cables (e.g. for prove of concept).

In any case, I think it's a cool use of the kill-command. One I didn't know of.

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For those who've seen my presentation on MySQL HA, you already know that I often use a multimaster setup with a meta OCF resource that groups my favoured MySQL instance with the service ip , using a meta resource means that pacemaker monitors mysql, but it doesn't actually manage it. It's an approach that works for us.

One of the other approaches I will be looking at soon is the freshly released OCF resource that Florian announced last week.

Back in the days our approach meant we didn't have to use clone resources, which you might remember being pretty buggy in the v2 era, not wanting to use clons resources isn't really a valid reason anymore these days . I've also frequently mentioned the combination of using DRBD and MultiMaster replication, using this set of OCF resource makes that a lot more easy ..

Now all I need to do is find me some time to validate this setup.

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You are using MySQL Cluster and crazy enough to digest NDB API? Sick of SQL? Here's a treat: a function to make C/C++ strings ready for inserting into a VARCHAR field. The special thing about them is that the length is prefixed in the first 2 bytes.

void make_ndb_varchar(char *buffer, char *str)
{
  int len = strlen(str);
  int hlen = (len > 255) ? 2 : 1;
  buffer[0] = len & 0xff;
  if( len > 255 )
    buffer[1] = (len / 256);
  strcpy(buffer+hlen, str);
}

Yes, you can use memcpy. Whatever floats your boat.

Lets use this function for a table t1, defined as follows (note: latin1!):

CREATE TABLE t1 (
  id INT UNSIGNED NOT NULL,
  vc VARCHAR(128),
  vclong VARCHAR(1280),
  PRIMARY KEY (id)
  ) ENGINE=NDB DEFAULT CHARSET=latin1

Here is part of the code, simplified for this post:

char vc[128+1]; // Size of 'vc', +1 for length info
 char vclong[1280+2]; // Size of 'vclong', +2 for length info
 ..
 make_ndb_varchar(vc, "NDB API kicks ass");
 operation->setValue("vc", vc);
 ..

The above example uses latin1. You could use Unicode, but that would probably mean converting from one encoding to the other using iconv. That's another story.

This post complements Johan Andersson's blog entry. Thanks to my colleagues Mats and Roger who helped me with a silly problem today regarding this function.

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Most software people are aware of the ACID acronym coined by Jim Gray. With the growth of the web and open source, the scaling and complexity constraints imposed on DBMS implementations supporting ACID are more visible, and new (or at least new terms for known) compromises and tradeoffs are being discussed widely. The better known NoSQL systems are giving insight by example into particular choices of tradeoffs.

Working at MySQL, I have often been surprised at the variety of potential alternatives when implementing a DBMS, and the number of applications which don't need the full set of ACID letters in the strictest form. The original MySQL storage engine, MyISAM is one of the first and most successful examples of an 'ACID remix'. The people drawn to DBMS development work often have a perfectionist streak, which can cause them to tend to prefer 'nothing' over 'imperfect'. MyISAM was and still is a flag-bearer for 'good enough'. Perhaps we should be less modest and call it 'more than good enough'.

One seldom discussed benefit of MySQL's storage engine architecture is that pressure to make 'The One True Storage Engine' is reduced. DBMS products with one fixed database engine need to optimise for all supported use cases. This is a great engineering challenge, but increases design effort, requirements for configuration and auto-tuning, constraints on any design change or reoptimisation etc. With MySQL, there are multiple existing storage engines, each with a (sub)set of target use-cases in mind. A single MySQL server can maintain and access tables in different storage engines, each tuned as closely as possible to the use-case for the data, without adding complexity to unrelated engines. Engines can be wildly optimised for a narrow use case as there are plausible alternative engines available for other use cases.

I understand that one aim of the Drizzle project is to extend the modularity of the MySQL Server on multiple axes, allowing diversity to flourish. As a one-time Java coder, who enjoyed the pleasures of design-by-interface, I can see the attraction. While the effort is guided by an actual need for modularity and real examples of alternative plugins, it can be a great force multiplier. There is always the risk of modularity for its own sake - a branch of Architecture Astronautics. Sure symptoms, which I may have suffered from in the past, include the class names FactoryFactory..., PolicyPolicy, or [Anything]Broker).

Another good vibe from Drizzle is the microkernel concept, although would say that there's some terminological abuse occurring here! Perhaps it could more reasonably be said that MySQL has a TeraKernel and Drizzle has a MegaKernel? In any case the motivations are good. Decoupling the huge chunks of functionality glued together inside MySQLD is great for long term software integrity, understanding dependencies, finding (and introducing) bugs, and might make it easier to start adding functionality again. Replication seems especially ripe ground for alternative plugins. User authentication is another often requested 'chunk'. It will take longer to crystalise interfaces for more deeply embedded areas like the query Optimizer/Executor, but if these interfaces are arising from a real need then that can drive the API design.

One aspect of storage engine modularity that is not often mentioned is that some MySQL storage engines also moonlight with other products. The Berkeley database (BDB) is probably the oldest and most promiscuous, embedded in DNS daemons, LDAP servers and all sorts of other places. Ndb is unusual in that it can be used from separate MySQLD and other NdbApi processes at the same time. InnoDB has also recently added an embedded variant. This trend will accelerate, especially when some of the distributed NoSQL systems start supporting 'pluggable local storage' APIs. I imagine that a NoSQL local storage engine API could be somewhat simpler to implement than the MySQL SE API, at least to start with!

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Shortly after I posted my last summary of MySQL releases, our son Mats was born and I went on a 2.5-week vacation. Our developers did not rest in the meanwhile and I'd like to give you a quick update of what's new since then:

MySQL Connector/Net 6.3.0

• Visual Studio 2010 RC support
• Nested transaction scope support

MySQL Workbench 5.2.16 Beta 6

• Fixed 67 bugs
• Saving your profile/connection passwords in OSX keychain, gnome-keyring or in an encrypted password-vault-file.
• New rapid development features for generating complete SQL Select/DML statements or names for selected objects in Query Editor to either the query area or clipboard.
• The ability to set a preference for the placement  (left or right side) of the sidebar in the Query Editor (Currently on Windows only, coming to Mac and Linux soon).
• Further optimization and stabilization of the administrator components

MySQL Server 5.1.44

• This release now includes InnoDB Plugin version 1.0.6, wich is considered to be of Release Candidate (RC) quality.
• Lots of bug fixes - see the ChangeLog for details.

MySQL Server 5.5.2 Milestone 2

• Also includes the updated InnoDB Plugin 1.0.6 and several fixes - see the ChangeLog for details. For an overview of new features in the 5.5 code base, check out the "What's new in 5.5" page in the reference manual.

Please note that the MySQL downloads section has been split into two parts. As usual, you will find downloads of both GA and development versions of all MySQL products and releases on the MySQL DevZone. In addition to that, we've now added a pointer to the downloads of officially released (GA) versions to the main web site on http://www.mysql.com/downloads/.

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