MongoDB Experience: Replication 101

After successfully installing and testing mongoDB it’s very easy to create a replication environment.

$ mkdir -p data/{master,slave}
$ mongod --dbpath=`pwd`/data/master --master --port 28011 > master.log 2>&1 &
# Always check your log file
$ cat master.log
$ mongod --dbpath=`pwd`/data/slave --slave --source localhost:28011 --port 28022 > slave.log 2>&1 &
$ cat slave.log

The options are relatively descriptive and straightforward.

  • –dbpath – The directory for data (we set because we are running master/slave on same server)
  • –port – Likewise we are running multiple instances on same machine
  • –master – I’m the master
  • –slave – I’m a slave
  • –source – For slaves, tell them were the source (i.e. master is)

What I found under the covers was a difference from the single instance version. There is a series of ‘local’ files for the namespace, where in the single instance version there were ‘test’ files.

$ ls -ltR data
total 0
drwxr-xr-x  6 rbradfor  staff  204 Jun 10 10:24 slave
drwxr-xr-x  5 rbradfor  staff  170 Jun 10 10:22 master

data/slave:
total 163848
drwxr-xr-x  2 rbradfor  staff        68 Jun 10 10:24 _tmp
-rw-------  1 rbradfor  staff  67108864 Jun 10 10:24 local.0
-rw-------  1 rbradfor  staff  16777216 Jun 10 10:24 local.ns
-rwxr-xr-x  1 rbradfor  staff         6 Jun 10 10:24 mongod.lock

data/slave/_tmp:

data/master:
total 163848
-rw-------  1 rbradfor  staff  67108864 Jun 10 10:22 local.0
-rw-------  1 rbradfor  staff  16777216 Jun 10 10:22 local.ns
-rwxr-xr-x  1 rbradfor  staff         6 Jun 10 10:22 mongod.lock

A quick replication test.

$ mongo --port 28011
MongoDB shell version: 1.4.3
url: test
connecting to: 127.0.0.1:28011/test
type "help" for help
> db.foo.save({s:"Hello world"});
> db.foo.find();
{ "_id" : ObjectId("4c10f7904a30c35548b0af06"), "s" : "Hello world" }
> exit
bye

$ mongo --port 28022
MongoDB shell version: 1.4.3
url: test
connecting to: 127.0.0.1:28022/test
type "help" for help
> db.foo.find();
{ "_id" : ObjectId("4c10f7904a30c35548b0af06"), "s" : "Hello world" }
> exit

A look now at the underlying data shows a ‘test’ namespace which confirms the lazy instantiation approach. The ‘local’ namespace files are obviously a reflection of the –master/–slave operation.

$ ls -ltR data
total 0
drwxr-xr-x  9 rbradfor  staff  306 Jun 10 10:32 slave
drwxr-xr-x  8 rbradfor  staff  272 Jun 10 10:32 master

data/slave:
total 589832
-rw-------  1 rbradfor  staff  134217728 Jun 10 10:33 test.1
drwxr-xr-x  2 rbradfor  staff         68 Jun 10 10:32 _tmp
-rw-------  1 rbradfor  staff   67108864 Jun 10 10:32 test.0
-rw-------  1 rbradfor  staff   16777216 Jun 10 10:32 test.ns
-rw-------  1 rbradfor  staff   67108864 Jun 10 10:24 local.0
-rw-------  1 rbradfor  staff   16777216 Jun 10 10:24 local.ns
-rwxr-xr-x  1 rbradfor  staff          6 Jun 10 10:24 mongod.lock

data/master:
total 327688
drwxr-xr-x  2 rbradfor  staff        68 Jun 10 10:32 _tmp
-rw-------  1 rbradfor  staff  67108864 Jun 10 10:32 test.0
-rw-------  1 rbradfor  staff  16777216 Jun 10 10:32 test.ns
-rw-------  1 rbradfor  staff  67108864 Jun 10 10:22 local.0
-rw-------  1 rbradfor  staff  16777216 Jun 10 10:22 local.ns
-rwxr-xr-x  1 rbradfor  staff         6 Jun 10 10:22 mongod.lock

By default there appears to be no read-only default state for a slave. I was able to add new data to the slave.

$ mongo --port 28022
MongoDB shell version: 1.4.3
url: test
connecting to: 127.0.0.1:28022/test
type "help" for help
> db.foo.save({s:"Hello New York"});
> db.foo.find();
{ "_id" : ObjectId("4c10f7904a30c35548b0af06"), "s" : "Hello world" }
{ "_id" : ObjectId("4c10f864d8e80f1a1ad305cf"), "s" : "Hello New York" }
>

A closer look at this ‘local’ namespace and a check via the docs gives us details of the slave configuration.

$ mongo --port 28022
MongoDB shell version: 1.4.3
url: test
connecting to: 127.0.0.1:28022/test
type "help" for help
> show dbs;
admin
local
test
> use local;
switched to db local
> show collections;
oplog.$main
pair.sync
sources
system.indexes
> db.sources.find();
{ "_id" : ObjectId("4c10f5b633308f7c3d7afc45"), "host" : "localhost:28011", "source" : "main", "syncedTo" : { "t" : 1276180895000, "i" : 1 }, "localLogTs" : { "t" : 1276180898000, "i" : 1 } }

You can also with the mongo client connect directly to a collection via the command line.

$ mongo localhost:28022/local
MongoDB shell version: 1.4.3
url: localhost:28022/local
connecting to: localhost:28022/local
type "help" for help
> db.sources.find();
{ "_id" : ObjectId("4c10f5b633308f7c3d7afc45"), "host" : "localhost:28011", "source" : "main", "syncedTo" : { "t" : 1276180775000, "i" : 1 }, "localLogTs" : { "t" : 1276180778000, "i" : 1 } }
> exit
bye

The shell gives 3 convenience commands for showing replication state.

On the Slave

$ mongo --port 28022
> db.getReplicationInfo();
{
	"logSizeMB" : 50,
	"timeDiff" : 1444,
	"timeDiffHours" : 0.4,
	"tFirst" : "Thu Jun 10 2010 10:24:54 GMT-0400 (EDT)",
	"tLast" : "Thu Jun 10 2010 10:48:58 GMT-0400 (EDT)",
	"now" : "Thu Jun 10 2010 10:48:59 GMT-0400 (EDT)"
}
> db.printReplicationInfo();
configured oplog size:   50MB
log length start to end: 1444secs (0.4hrs)
oplog first event time:  Thu Jun 10 2010 10:24:54 GMT-0400 (EDT)
oplog last event time:   Thu Jun 10 2010 10:48:58 GMT-0400 (EDT)
now:                     Thu Jun 10 2010 10:49:07 GMT-0400 (EDT)
> db.printSlaveReplicationInfo();
source:   localhost:28011
syncedTo: Thu Jun 10 2010 10:49:25 GMT-0400 (EDT)
          = 1secs ago (0hrs)

On the master, the same commands are applicable, output basically the same.

$ mongo --port 28011
> db.getReplicationInfo();
{
	"logSizeMB" : 50,
	"timeDiff" : 1714,
	"timeDiffHours" : 0.48,
	"tFirst" : "Thu Jun 10 2010 10:22:01 GMT-0400 (EDT)",
	"tLast" : "Thu Jun 10 2010 10:50:35 GMT-0400 (EDT)",
	"now" : "Thu Jun 10 2010 10:50:40 GMT-0400 (EDT)"
}
> db.printReplicationInfo();
configured oplog size:   50MB
log length start to end: 1714secs (0.48hrs)
oplog first event time:  Thu Jun 10 2010 10:22:01 GMT-0400 (EDT)
oplog last event time:   Thu Jun 10 2010 10:50:35 GMT-0400 (EDT)
now:                     Thu Jun 10 2010 10:50:45 GMT-0400 (EDT)
> db.printSlaveReplicationInfo();
local.sources is empty; is this db a --slave?
>

From these commands there seems no obvious way to easily identify if an instance is a master or not.

References

DBA operations from shell
Replication
Master/Slave Replication

ImageMagick on Mac OS X

Wanting to do some image manipulation I realized my Linux scripts don’t run under Mac OS X, as ImageMagick is not installed via my MacPorts.

However installation failed:

$ sudo port install imagemagick
--->  Computing dependencies for ImageMagick
--->  Verifying checksum(s) for xorg-libX11
Error: Checksum (md5) mismatch for libX11-1.3.3.tar.bz2
Error: Checksum (sha1) mismatch for libX11-1.3.3.tar.bz2
Error: Checksum (rmd160) mismatch for libX11-1.3.3.tar.bz2
Error: Target org.macports.checksum returned: Unable to verify file checksums
Error: The following dependencies failed to build: xorg-libXext xorg-libX11 xorg-libXt xorg-libsm xorg-libice
Error: Status 1 encountered during processing.
Before reporting a bug, first run the command again with the -d flag to get complete output.

Figuring that some of my packages may require upgrade:

$ sudo port selfupdate
sudo port -d upgrade outdated

The problem is this all failed. Turning to the FAQ it seemed what I needed to do was remove and re-install the offending package receiving the checksum error via the following syntax.

$ sudo port clean --all 
$ sudo port install 

It seemed I had to do this for several packages manually however in the end removing and installing a number of packages addressed the problem and now ImageMagick is happily running on Mac OS X

bash-3.2$ sudo port clean --all xorg-libX11
--->  Cleaning xorg-libX11
bash-3.2$ sudo port install xorg-libX11
---->  Computing dependencies for ImageMagick
--->  Verifying checksum(s) for xorg-libX11
Error: Checksum (md5) mismatch for libX11-1.3.3.tar.bz2
Error: Checksum (sha1) mismatch for libX11-1.3.3.tar.bz2
Error: Checksum (rmd160) mismatch for libX11-1.3.3.tar.bz2
Error: Target org.macports.checksum returned: Unable to verify file checksums
Error: The following dependencies failed to build: xorg-libXext xorg-libX11 xorg-libXt xorg-libsm xorg-libice
Error: Status 1 encountered during processing.
Before reporting a bug, first run the command again with the -d flag to get complete output.
bash-3.2$ sudo port clean --all libX11
Error: Port libX11 not found
Before reporting a bug, first run the command again with the -d flag to get complete output.
bash-3.2$ sudo port clean --all xorg-libX11
--->  Cleaning xorg-libX11
bash-3.2$ sudo port install xorg-libX11

Free MySQL Event in Washington DC

As the program chair for the recently announced MySQL Track at the ODTUG Kaleidoscope conference located in Washington DC we are also looking into an associated free community event for MySQL locals in addition to a dedicated track for 4 days.

Please let us know your name and email via the form at http://ronaldbradford.com/ODTUG/free-event/ so we can provide more details in the coming week as we try to finalize logistics.

Registration will be necessary for attendance however for now we just want to know who is local so we can provide more details soon!

Updated. Full details of the free Monday night sundown sessions and reception can be found at MySQL track with free event at Kaleidoscope 2010

State of the Dolphin – Opening keynote

Edward Screven – Chief Corporate Architect of Oracle provided the opening keynote at the 2010 MySQL Users Conference.

Overall I was disappointed. The first half was more an Oracle Sales pitch, we had some product announcements, we had some 5.5 performance buzz. While a few numbers and features were indeed great to hear, there was a clear lack of information to the MySQL ecosystem including employees, alumni and various support services. I hope more is unveiled this week.

Some notes of the session.

  • Oracle’s Strategy covers storage, servers, virtual machines, operating system, database, middleware, applications
  • We build a complete technology stack that is “open” and “integrated” based on “open standards”
  • products talk via open standards with the intention for customers to not feel locked in to any technology
  • Examples include apache, java, linux, xen, eclipse, and innodb
  • Unbreakable linux has now over 4,500 customers

After the sales pitch we got down to more about MySQL.

What MySQL means to Oracle? We make the Oracle solution more complete as a stack for customers.

What is the investment in MySQL?

  • Make MySQL a better MySQL
  • Develop, promote and support MySQL
  • MySQL community edition

Integration with Oracle Enterprise Manager, Oracle Secure Backup and Oracle Audit Vault infrastructure. *This I expected and have blogged about, so I’m glad to see this commitment.

MySQL 5.5 is now in Alpha, some features are

  • InnoDB will be default engine
  • Semi sync replication
  • Replication heartbeat
  • Signal
  • Performance Schema

MySQL 5.5 is planned on being faster with Innodb Performance Improvements & MySQL Performance Improvements.
MySQL 5.5 sysbench claims, read 200% faster, write 364% faster.

MySQL Workbench 5.2 announcement

  • SQL Development
  • Database Administration
  • Data Modelling

MySQL Cluster 7.1 GA announcement

  • Improved Administration
  • Higher Performance
  • Carrier Grade Availability & Performance

MySQL Enterprise Backup announcement

  • Online backup for InnoDB only
  • Formally InnoDB hot backup with additional features including incremental backups

MySQL Enterprise Monitor 2.2 Beta announcment

In closing the statement was “MySQL lets Oracle be more complete at the database layer”. Is that good for the MySQL Community or better for the Oracle revenue model?

New linux desktop configuration

My purchase yesterday was a HP Pavilion p6340f Desktop PC with the following specs.

  • Intel Core 2 Quad Q8400 2.66GHz Processor
  • 4MB L2 Cache, 1333MHz FSB
  • 8GB PC3-8500 DDR3 SDRAM (4 x 2GB)
  • 1TB Serial ATA Hard Drive
  • Intel Graphics Media Accelerator X4500 with 32MB Integrated shared graphics memory
  • Lightscribe SuperMulti DVD±R/RW with Double Layer
  • 10/100/1000 Base-T Network interface
  • Wireless LAN 802.11 a/b/g/n

The purchase price $749+tax which was more then B&H at $699 but not being open Friday nights, B&H it’s your loss. There is also a P6320 model with AMD Phenom II X4 820 2.80GHz processor and NVIDIA GeForce 9100 Graphics for the same price, it was a tough decision.

I’m not trilled with the HP part having not enjoyed experiences with HP servers and Compaq desktops, however time will tell.

Upgrading my Google G1 dev phone to Android 1.6

To update your Google G1 phone (mine is an Android developer unlocked phone) to Android 1.6 (Donut), I did the following.

  • Download and unpack the Android SDK for Mac OS X from http://developer.android.com/sdk/index.html
  • Download the Android 1.6 Radio and System Images from http://developer.htc.com/adp.html
  • Reboot phone with USB connected
  • Update the Device Radio Firmware
    • Confirm devices with $ adb devices This step drove me crazy because it would list no devices. It ended up being a faulty (and new) USB cable. When your phone is connected to USB, it will give you a notification, and usb icon on phone top menu.
    • Copy Radio image
    • Reboot in recovery mode and follow instructions
  • Download the fastboot for Mac OS X at http://developer.htc.com/adp.html
  • Flash the System Image Package to the Device as per instructions

The instructions say to reboot, but in my case it rebooted automatically after the fastboot update.

The problem after reboot was I was unable to sign in to google servers the first time. At G1 Dev Phone won’t connect to Google servers with valid SIM card I added the necessary AT&T/Cingular APN via details at http://modmyi.com/wiki/index.php/Carrier_APN_Settings.

I could then go Settings | Data synchronization and continue the Google registration process.

Getting started with Cassandra

With the motivation from today’s public news on Twitter’s move from MySQL to Cassandra, my own skills desire following in-depth discussions at last November’s Open SQL Camp to consider Cassandra and yesterday’s discussion with a new client on persistent key-value store products, today I download installed and configured for the first time. Not that today’s news was unexpected, if you follow the Twitter Engineering Open Source projects you would have seen Cassandra as well as other products being used or evaluated by Twitter.

So I went from nothing to a working Cassandra node in under 5 minutes. This is what I did.

  1. While I knew this was an Apache project, a Google Search yields for me the 3rd link for the The Apache Cassandra Project at http://incubator.apache.org/cassandra/. Congrats for Cassandra now a top level Apache Project. This url will update soon.
  2. Download Cassandra. Hard to miss with a big green button on home page. Current version is 0.5
  3. I read Getting Started, which is the 3rd top level link on menu after Home and Download. Step 1 is picking a version which I’ve already done, Step 2 is Running a single node.
  4. The Getting Started indicated a problem on Mac OS X for the required minimum Java version. I was installing on Mac OS X 10.5 and CentOS 5.4. I’ve experienced this Java 6 default path issue before. Set my JAVA_HOME and PATH accordingly (after I updated the wiki with correct value)
  5. I extracted the tar file, changed to the directory and took at look at the README.txt file. Yes, I always check this first with any software and relevant because it includes valuable instructions on creating the default data and log directories.
  6. Start with bin/cassandra -f. No problems!
  7. I then followed the instructions from the link in Step 2 with the CassandraCli. This tests and confirms the installation is operational.

Ok, a working environment. I’ve now installed on a second machine and tested however I now need to configure the cluster, and the documentation is not as straightforward. Time to try out Google again.

On a side note, this is one reason why I love Open Source. I followed the instructions online and found a mistake in the Mac OS X path, I simply registered and corrected providing the benefit of my experience for the next reader(s).

You may also like to view future posts including.

What's your MySQL version?

I’ve heard that the mechanic’s wife always has a car that needs repair or tuneup, the painter’s wife always had walls of peeling paint, you get the picture. What about MySQL DBA’s and their own databases? While I have many versions of MySQL for testing including for example the latest 5.1.44 which I was using for my previous post, what is running on my production server? Let’s see:

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.1.25-rc |
+-----------+

That’s really old. And yes, to prove my point that we can be our own worst enemy, the previous version before 5.1.25 was 5.1.6. Yes, .6 which worked just fine, and never crashed once for my 20+ websites. While I have downloaded onto my production server several versions ready for upgrade including versions 5.1.30, 5.1,38, and 5.4.1 I’ve never actually gone through the upgrade process.

Migrating MySQL latin1 to utf8 – Character Set Options

Continuing on from preparation in our MySQL latin1 to utf8 migration let us first understand where MySQL uses character sets. MySQL defines the character set at 4 different levels for the structure of data.

  • Instance
  • Schema
  • Table
  • Column

In MySQL 5.1, the default character set is latin1. If not specified, this is what you will get. For example.

mysql> create table test1(c1 varchar(10) not null);
mysql> show create table test1G
Create Table: CREATE TABLE `test1` (
  `c1` varchar(10) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1

If you want all tables in your instance to always be a default of utf8, you can changed the server variable character_set_server. This can be set dynamically.

mysql> set global character_set_server=utf8;
mysql> set session character_set_server=utf8;
mysql> create table test2(c1 varchar(10) not null);
mysql> show create table test2G
Create Table: CREATE TABLE `test2` (
  `c1` varchar(10) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8

If you change this dynamically be sure to include the option in your my.cnf to ensure this option is persisted for a mysqld restart.

You can define the default character set for all new tables in a given schema. You specify this when you create the schema.

mysql> set global character_set_server=latin1;
mysql> set session character_set_server=latin1;
mysql> create schema test_ucs2 default character set ucs2;
mysql> use test_ucs2;
mysql> create table test3(c1 varchar(10) not null);
mysql> show create table test3G
Create Table: CREATE TABLE `test3` (
  `c1` varchar(10) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=ucs2

Even though we have a schema default, you can always specify the default character set for a given table which overrides any defaults.

mysql> use test_ucs2;
mysql> create table test4_utf8 (c varchar(10) not null) default charset utf8;
mysql> show create table test4_utf8G
Create Table: CREATE TABLE `test4_utf8` (
  `c` varchar(10) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8

And finally, if you really wanted to be specific you can define the character set on a per column level.

mysql> create table test4_utf8_latin1 (c varchar(10) not null, c2 varchar(20) charset latin1) default charset utf8;
mysql> show create table test4_utf8_latin1G
*************************** 1. row ***************************
       Table: test4_utf8_latin1
Create Table: CREATE TABLE `test4_utf8_latin1` (
  `c` varchar(10) NOT NULL,
  `c2` varchar(20) CHARACTER SET latin1 DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8

With great flexibility comes great responsibility. You should have a defined standard for your application that is simple and easy to understand. I am not a proponent of using utf8 for everything, the primary reason why is memory. As part of my consulting I spend a lot of time with clients that have limited resources, e.g. database servers with 2GB or 4GB of RAM. MySQL stores utf8 efficiently on disk, but when this data is stored in memory for internal usage, it automatically uses 3 bytes, when on disk it may only be 1 byte. You can test this by creating a MEMORY table with latin1 and utf8 examples and comparing the difference in size. Is this a serious problem? Well that depends on many factors such as the number of database connections, persistent or not persistent connections, the size of the results etc. While it’s difficult in MySQL to instrument the memory precisely on a per connection basis, prudence should be a consideration for any physical resources, especially RAM.

Now that we understand what’s possible, how can we change our existing latin1 tables in our preparation example?

We could try a simple ALTER TABLE command.

mysql> alter table test_latin1 default charset utf8;
mysql> show create table test_latin1G
Create Table: CREATE TABLE `test_latin1` (
  `c` varchar(100) CHARACTER SET latin1 NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8

This does not work, because we are only changing the default storage engine of the table. The underlying columns remain the same. If we were to add a new column, it would default to utf8. We can however achieve what we expected with the CONVERT option.

mysql> alter table test_latin1 convert to character set utf8;
mysql> show create table test_latin1G
Create Table: CREATE TABLE `test_latin1` (
  `c` varchar(100) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8

We look at our data, and it looks great? Are we done with our conversion?

mysql> select * from test_latin1;
+---------------+
| c             |
+---------------+
| a             |
| abc           |
| ☺           |
| abc ☺☹☻ |
+---------------+

The answer is no. While it may look like the data is correct, MySQL also manages character sets for the communication channel. In this case, we are still communicating in latin1. To ensure moving forward in the future we must always communicate in utf8 to ensure we correctly pass utf8 to the database. We can test this with the mysql client, and as you will see our data is still corrupt.

mysql> set names utf8;
mysql> select * from test_latin1;
+------------------------+
| c                      |
+------------------------+
| a                      |
| abc                    |
| ☺                 |
| abc ☺☹☻ |
+------------------------+

mysql> show session variables like 'character%';
+--------------------------+----------------------------------------------------------------+
| Variable_name            | Value                                                          |
+--------------------------+----------------------------------------------------------------+
| character_set_client     | utf8                                                           |
| character_set_connection | utf8                                                           |
| character_set_database   | latin1                                                         |
| character_set_filesystem | binary                                                         |
| character_set_results    | utf8                                                           |
| character_set_server     | latin1                                                         |
| character_set_system     | utf8                                                           |
+--------------------------+----------------------------------------------------------------+

While you can see how we could migrate the schema definition, this does not complete our migration. In my next post, I will discuss the various different ways to correctly perform a data migration between latin1 and utf8.

Checked your MySQL recovery process recently?

I sound like a broken record with every client when I talk to about the resilience of their production environments. It’s very simple in theory, however in practice many organizations fail.

Ask yourself these checklist questions for your MySQL backup and recovery process?

  1. Do you have MySQL backups in place?
  2. Do you backup ALL your MySQL data?
  3. Do you have consistent MySQL backups?
  4. Do you have backups that include both static snapshot and point in time transactions?
  5. Do you review your backup logs EVERY SINGLE day or have tested backup monitoring in place?
  6. Do you perform a test recovery of your static backup?
  7. Do you perform a test recovery to point in time?
  8. Do you time your backup and recovery process and review over time?
  9. Do you have off-site copies of your backups?
  10. Do you backup your primary binary logs?

In the past month I’ve discovered clients that have an online only business (i.e. Their MySQL data is their only tangible asset), they perform daily backups but they don’t have binary logging enabled. I’ve also discovered an example of backup logs not being checked, and an underlying mysqldump error was resulting in an incomplete backup, yet the backup script apparently completed successfully.

Disaster is inevitable.

If you don’t score 8 or better in the above checklist in your business, you are at higher risk. If you are a owner/founder/executive this should keep you awake at night if your not sure of your business viability. If your organization needs help, please contact me for assistance.

  • Can you recover from a small or large disaster?
  • Do you have confidence in your DR plan?
  • Do you know how long your DR plan will take.
  • What does your online business look like or operate during your DR time?

Migrating MySQL latin1 to utf8 – Preparation

This article is Part 1 of a series of articles regarding MySQL character set conversion.
Be sure to also check out character set options and the process for more information.

Before undertaking such migration the first step is a lesson in understanding more about how latin1 and utf8 work and interact in MySQL. latin1 in a common and historical character set used in MySQL. utf8 (first available in MySQL Version 4.1) is an encoding supporting multiple bytes and is the system default in MySQL 5.0

  • latin1 is a single byte character set.
  • utf8 is a 1-3 byte character set depending on the size of the character. NOTE: MySQL utf8 does not support the RFC 3629 4 byte sequences. (Updated: MySQL 5.5 now supports full Unicode support with the ” utf8m4″charset))

MySQL variables

MySQL has a number of different system variables to consider, the following is the default representation in MySQL 5.1

mysql> show global variables like '%char%';
+--------------------------+----------------------------------------------------------------+
| Variable_name            | Value                                                          |
+--------------------------+----------------------------------------------------------------+
| character_set_client     | latin1                                                         |
| character_set_connection | latin1                                                         |
| character_set_database   | latin1                                                         |
| character_set_filesystem | binary                                                         |
| character_set_results    | latin1                                                         |
| character_set_server     | latin1                                                         |
| character_set_system     | utf8                                                           |
+--------------------------+----------------------------------------------------------------+

MySQL enables you to specify the character set for data at the Instance,Schema,Table and Column level. This is important because this complexity, especially between the Table and Columns can catch you out.

It is also important to ensure that not only is data stored in the appropriate format, the communication between client and server also needs to support the character set you wish to use.

latin1 example

We start by creating a simple table, inserting some data, and reviewing the data.

mysql> create table test_latin1(c varchar(100) not null) default charset latin1;
mysql> insert into test_latin1(c) values ('a'),('abc'),('☺'),('abc ☺☹☻');

mysql> select c,length(c),char_length(c),charset(c),hex(c) from test_latin1;
+---------------+-----------+----------------+------------+----------------------------+
| c             | length(c) | char_length(c) | charset(c) | hex(c)                     |
+---------------+-----------+----------------+------------+----------------------------+
| a             |         1 |              1 | latin1     | 61                         |
| abc           |         3 |              3 | latin1     | 616263                     |
| ☺             |         3 |              3 | latin1     | E298BA                     |
| abc ☺☹☻       |        13 |             13 | latin1     | 61626320E298BAE298B9E298BB |
+---------------+-----------+----------------+------------+----------------------------+
4 rows in set (0.00 sec)

We use the LENGTH() and CHAR_LENGTH() functions to confirm the known length of the string and the true number of characters.

In the above examples, the smiley characters can be reproduced in a web page with the following.

☺☹☻

utf8 example

In a separate session (because we re-use these later) we repeat for utf8.

mysql> set  names utf8;
mysql> show session variables like '%char%';
+--------------------------+----------------------------------------------------------------+
| Variable_name            | Value                                                          |
+--------------------------+----------------------------------------------------------------+
| character_set_client     | utf8                                                           |
| character_set_connection | utf8                                                           |
| character_set_database   | latin1                                                         |
| character_set_filesystem | binary                                                         |
| character_set_results    | utf8                                                           |
| character_set_server     | latin1                                                         |
| character_set_system     | utf8                                                           |
+--------------------------+----------------------------------------------------------------+

mysql> create table test_utf8(c varchar(100) not null) default charset utf8;
mysql> insert into test_utf8(c) values ('a'),('abc'),('☺'),('abc ☺☹☻');

mysql> select c,length(c),char_length(c),charset(c), hex(c) from test_utf8;
+---------------+-----------+----------------+------------+----------------------------+
| c             | length(c) | char_length(c) | charset(c) | hex(c)                     |
+---------------+-----------+----------------+------------+----------------------------+
| a             |         1 |              1 | utf8       | 61                         |
| abc           |         3 |              3 | utf8       | 616263                     |
| ☺            |         3 |              1 | utf8       | E298BA                     |
| abc ☺☹☻       |        13 |              7 | utf8       | 61626320E298BAE298B9E298BB |
+---------------+-----------+----------------+------------+----------------------------+
4 rows in set (0.00 sec)

As you can see, the key difference here is the CHAR_LENGTH() of the utf8 strings differ.

Mixing latin1 with utf8

If we now look at the latin1 data in the utf8 session we see that while the underlying data via LENGTH(),CHAR_LENGTH() and HEX() remains unchanged (because this is the database representation of the data), the actual output presentation is garbled due to the mismatch in the client communication.

mysql> select c,length(c),char_length(c),charset(c), hex(c) from test_latin1;
+------------------------+-----------+----------------+------------+----------------------------+
| c                      | length(c) | char_length(c) | charset(c) | hex(c)                     |
+------------------------+-----------+----------------+------------+----------------------------+
| a                      |         1 |              1 | latin1     | 61                         |
| abc                    |         3 |              3 | latin1     | 616263                     |
| ☺                    |         3 |              3 | latin1     | E298BA                     |
| abc ☺☹☻          |        13 |             13 | latin1     | 61626320E298BAE298B9E298BB |
+------------------------+-----------+----------------+------------+----------------------------+
4 rows in set (0.00 sec)

If we look at the utf8 data in latin1, we see a different garbled representation.

mysql> select c,length(c),char_length(c),charset(c),hex(c) from test_utf8;
+---------+-----------+----------------+------------+----------------------------+
| c       | length(c) | char_length(c) | charset(c) | hex(c)                     |
+---------+-----------+----------------+------------+----------------------------+
| a       |         1 |              1 | utf8       | 61                         |
| abc     |         3 |              3 | utf8       | 616263                     |
| ?       |         3 |              1 | utf8       | E298BA                     |
| abc ??? |        13 |              7 | utf8       | 61626320E298BAE298B9E298BB |
+---------+-----------+----------------+------------+----------------------------+
4 rows in set (0.00 sec)

Conclusion

Armed now with a basic understanding we are ready to consider what approaches we may undertake to migrate this example table, and how we may be able to verify our data.

References

Character Set Support
Connection Character Sets and Collations

Beyond MySQL GA: patches, storage engines, forks, and pre-releases – FOSDEM 2010

Kristian Nielsen presented “Beyond MySQL GA: patches, storage engines, forks, and pre-releases”.
This included a history of current products:

Google Patches (5.0 & 5.1) included improvements in :

  • statistics/monitoring
  • lock contention
  • binlog
  • malloc()
  • filesorts
  • innodb I/O and wait statistics
  • SHOW …STATISTICS statements
  • smp scalability
  • I/O scalability
  • semisync replication
  • many more

Percona Patches (5.0) focus on

  • statistics/monitoring
  • performance/scalability
  • buffer pool content/mutexes
  • microslow patch

These have been ported to 5.1 and mainly integrated into XtraDB.

EBay Patches (5.0) have included:

  • variable length memory storage engine
  • pool of threads
  • Virtual columns

XtraDB storage engine (5.1) includes

  • Percona patches
  • Google patches
  • Innodb patches
  • Has XtraBackup for backup

Other engines/patches discussed included:

  • PBXT storage engine – community contribution
  • FederatedX – replacement to Federated
  • Sphinx storage engine
  • Pinba storage engine – Collects PHP statistics
  • Others OQGraph/Spider
  • Galera – Synchronous replication
  • Drizzle

Alternative packaging options for MySQL 5.0 and MySQL 5.1 including Our Delta, Percona and MariaDB.

FOSDEM 2010 MySQL Developer Room Schedule
FOSDEM 2010 Website
Brussels, Belgium
February 7, 2010

10x Performance Improvements in MySQL – A Case Study

The slides for my presentation at FOSDEM 2010 are now available online at slideshare. In this presentation I describe a successful client implementation with the result of 10x performance improvements. My presentation covers monitoring, reviewing and analyzing SQL, the art of indexes, improving SQL, storage engines and caching.

The end result was a page load improvement from 700+ms load time to a a consistent 60ms.

Be sure to know your my.cnf [sections]

The MySQL configuration file, e.g. /etc/my.cnf has a number of different section headings including [mysql], [mysqld], [mysqld_safe]. It is important that you ensure you put the right variables into the right section. For example, the following my.cnf configuration file will not operate as the user probably expects.

[mysqld]
...
log-bin=mysql-bin
server-id=1
query_cache_size = 100M
query_cache_type = 1

...

[mysqld_safe]
...
key_buffer_size=600M
skip-innodb
...

In this example, this configuration does not give you a MyISAM key buffer of 600M, it’s actually the default of 8M.

mysql> show global variables like 'key_buffer_size';
+-----------------+---------+
| Variable_name   | Value   |
+-----------------+---------+
| key_buffer_size | 8388600 |
+-----------------+---------+

Be sure to add the right options to the [mysqld] section.

What I didn’t know until yesterday was that some programs read from multiple groups. From the 5.1.2. Server Command Options MySQL reference manual page. In helping the describe the problem for the benefit of readers I actually learned something new myself.


mysqld reads options from the [mysqld] and [server] groups. mysqld_safe reads options from the [mysqld], [server], [mysqld_safe], and [safe_mysqld] groups. mysql.server reads options from the [mysqld] and [mysql.server] groups.

I have for example always put log-error in both the [mysqld_safe] and [mysql]d sections because both of these write different errors. Seems that is unnecessary.

Problem of the day, DESC gives error.

I hit this interesting problem last night on 5.0.51a.

mysql> use information_schema;
mysql> desc routines;
ERROR 1 (HY000): Can't create/write to file '/home/tmp/#sql_fea_1.MYD' (Errcode: 24)
mysql> show create table routinesG
*************************** 1. row ***************************
       Table: ROUTINES
Create Table: CREATE TEMPORARY TABLE `ROUTINES` (
  `SPECIFIC_NAME` varchar(64) NOT NULL default '',
  `ROUTINE_CATALOG` varchar(512) default NULL,
  `ROUTINE_SCHEMA` varchar(64) NOT NULL default '',
  `ROUTINE_NAME` varchar(64) NOT NULL default '',
  `ROUTINE_TYPE` varchar(9) NOT NULL default '',
  `DTD_IDENTIFIER` varchar(64) default NULL,
  `ROUTINE_BODY` varchar(8) NOT NULL default '',
  `ROUTINE_DEFINITION` longtext,
  `EXTERNAL_NAME` varchar(64) default NULL,
  `EXTERNAL_LANGUAGE` varchar(64) default NULL,
  `PARAMETER_STYLE` varchar(8) NOT NULL default '',
  `IS_DETERMINISTIC` varchar(3) NOT NULL default '',
  `SQL_DATA_ACCESS` varchar(64) NOT NULL default '',
  `SQL_PATH` varchar(64) default NULL,
  `SECURITY_TYPE` varchar(7) NOT NULL default '',
  `CREATED` datetime NOT NULL default '0000-00-00 00:00:00',
  `LAST_ALTERED` datetime NOT NULL default '0000-00-00 00:00:00',
  `SQL_MODE` longtext NOT NULL,
  `ROUTINE_COMMENT` varchar(64) NOT NULL default '',
  `DEFINER` varchar(77) NOT NULL default ''
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

I tried in on my MySQL 5.1 server without incident. In a few minutes of thinking about it, I was unable to determine the problem. Anybody care to guess?

What do MySQL staff think of the acquisition?

It finally dawned on me while reflecting on the year past this Sunday that the missing voice since the announcement of the Oracle acquisition of Sun Microsystems (and therefore MySQL) has been the MySQL employees.

When I worked as an employee for MySQL Inc, the acquisition by Sun Microsystems in 2008 lead to several requirements about the acquisition.

  • You were not allowed to talk about the acquisition publically.
  • You were not allowed to communicate with any Sun (i.e. the acquirer) resources.

In other words it was “business as usual” which is really an oxymoron, because business will never be exactly as it was before the announcement. The ongoing delay in pending acquisition by Oracle Corporation is really hurting everybody with getting on with doing their jobs, being happy with their work, and making a difference in open source and in the lives of all the benefit from using MySQL.

I’m sure many that have words to say are disappointed, worried or even fearful of their own future careers. Comments are always welcome via Mr Anonymous using 10 minute email.

Couldn't load plugin named 'innodb'

As part of reviewing storage engines for my work on the upcoming Expert PHP and MySQL book, I finally had an excuse to try out the InnoDB Plugin for MySQL which is now conveniently included with MySQL 5.1 since 5.1.38.

Following the MySQL 5.1 Reference Manual instructions at 13.6. The InnoDB Storage Engine I included the bare minimum as documented to my my.cnf.

[mysqld]
ignore-builtin-innodb
plugin-load=innodb=ha_innodb_plugin.so ;innodb_trx=ha_innodb_plugin.so ;innodb_locks=ha_innodb_plugin.so ;innodb_cmp=ha_innodb_plugin.so ;innodb_cmp_reset=ha_innodb_plugin.so ;innodb_cmpmem=ha_innodb_plugin.so ;innodb_cmpmem_reset=ha_innodb_plugin.so

However to my misfortune the following error occured.

091212 17:45:14 [ERROR] Can't open shared library '/home/rbradfor/mysql/mysql-5.1.41-linux-x86_64-glibc23/lib/plugin/ha_innodb_plugin.so ' (errno: 22 cannot open shared object file: No such file or directory)
091212 17:45:14 [ERROR] Couldn't load plugin named 'innodb' with soname 'ha_innodb_plugin.so '.

I double checked the files were indeed included in the binary release before undertaking a google search, to reveal the official Innodb Plugin Manual page but still not much to go on with the information ” Can’t open shared library library_name — Diagnose the cause from the following message details.”

Back to re-reading the error message, as referenced, I observed there is a trailing space ‘ ‘ ater the plugin name. Observing that I had indeed had this the my.cnf, the result of joining the lines from the MySQL manual which were broken down for presentation means (as noted).

Removed the space, and viola it works.

mysql> show plugins;
+---------------------+----------+--------------------+---------------------+---------+
| Name                | Status   | Type               | Library             | License |
+---------------------+----------+--------------------+---------------------+---------+
| binlog              | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| partition           | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| ARCHIVE             | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| BLACKHOLE           | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| CSV                 | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| FEDERATED           | DISABLED | STORAGE ENGINE     | NULL                | GPL     |
| MEMORY              | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| MyISAM              | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| MRG_MYISAM          | ACTIVE   | STORAGE ENGINE     | NULL                | GPL     |
| InnoDB              | ACTIVE   | STORAGE ENGINE     | ha_innodb_plugin.so | GPL     |
| INNODB_TRX          | ACTIVE   | INFORMATION SCHEMA | ha_innodb_plugin.so | GPL     |
| INNODB_LOCKS        | ACTIVE   | INFORMATION SCHEMA | ha_innodb_plugin.so | GPL     |
| INNODB_CMP          | ACTIVE   | INFORMATION SCHEMA | ha_innodb_plugin.so | GPL     |
| INNODB_CMP_RESET    | ACTIVE   | INFORMATION SCHEMA | ha_innodb_plugin.so | GPL     |
| INNODB_CMPMEM       | ACTIVE   | INFORMATION SCHEMA | ha_innodb_plugin.so | GPL     |
| INNODB_CMPMEM_RESET | ACTIVE   | INFORMATION SCHEMA | ha_innodb_plugin.so | GPL     |
+---------------------+----------+--------------------+---------------------+---------+

I would question that this level of pedantic checking is unnecessary. A simple trim on semi-colon ‘;’ separated values could be an easy fix.

Is your database schema in sync?

If you have more then a single MySQL database for your production environment, e.g. a development and test environment, or a MySQL replication topology, ensuring your schema’s are in sync can be task that requires some time if not managed correctly.

There is a tool I do use for MySQL environments called Schema Sync – a MySQL Schema Versioning and Migration Utility. There are many reasons why schema’s get out of sync. Developers may not ensure their changes are reflected in any software to be deployed, and when not tested you could end up with broken functionality. A DBA might try some different index strategies on a slave, but not the master, and never implement or revert.

While some people want the quick and hidden just sync version akin to Rails, I really like this product as it produces proper patch and revert SQL scripts. As a DBA I really want to know what’s going to be applied to my schema, I want to be able to review it before it’s just magically applied. The revert process is also ideal, in time critical situations when you may need to rollback a change, either it’s taking to long to deploy.

This is definitely a tool to use over time, especially if you have multiple developers, DBA’s and more then one MySQL environment that should be the same.

Monitoring MySQL with MONyog

It just works. In absence of any MySQL monitoring for your site, I have found no solution that gets you operational as quickly and easily. MONyog can be deployed in 60 seconds, and configured in another 60 seconds. Within 5 minutes you can have visual monitoring of your MySQL environment.

MONyog is an agentless process, which is an advantage for easy install, but does not provide for monitoring redundancy in the capture of information due to agentless nature. It’s a static standalone executable which is great if you need something to work out of the box. You can easily configure multiple servers in a replication topology, or different servers in your environment. You get the ability to monitor all the usual information, with a dashboard and detailed graphs. While MONyog does provide customizations of rules for the graphs and presentation order, that’s about it. You can’t at this time for example change the colors, what’s on graphs except for what MONyog monitors or the security of certain options in the GUI to different users, however I hope they offer these suggestions in future releases.

MONyog includes some nice features that are overlooked in other products. You have the ability to monitor the MySQL error log (if configured appropriately) which is a common complaint of end users. You can also see the process list, and when configured you can also perform query gathering and analysis.

MONyog is a well priced commercial product with a free trial download without registration requirements which gives no barrier to access and evaluate. As a solution and ease of deployment, there is no excuse not to evaluate this product. If you have no monitoring, you can now quickly and easily. I find a number of clients that simply have no monitoring. There really is no excuse as it’s critical information you need to have and record for a successful business.

You can get it from www.webyog.com.

MySQL Permissions – Restarting MySQL

I am working with a client that is using managed hosting on dedicated servers. This has presented new challenges in obtaining the right permissions to undertake MySQL tasks but not have either ‘root’ or ‘mysql’ access and not have to involve a third party everytime.

Adding the following to the /etc/sudoers file enabled the ability to restart MySQL.

User_Alias	DBA = rbradfor, user2, etc
Host_Alias 	DB_SERVERS = server1.example.com, server2.example.com, etc
Cmnd_Alias	MYSQL = /etc/init.d/mysqld, /usr/sbin/tcpdump

DBA DB_SERVERS = MYSQL

As you can see I also got tcpdump, which I find valuable to monitor via mk-query-digest.

Next, permissions for log files.

Monitoring MySQL resource limits

I have for the first time seen a client implement MySQL Resource Limits. I got the following error tying to connect to the database.

$ mysql -udba -p
ERROR 1226 (42000): User 'dba' has exceeded the 'max_user_connections' resource (current value: 10)

I see from the documentation the ability to see the limits in the mysql.user table. I see this is included in the SHOW GRANTS output.

SHOW GRANTS for 'dba'@'%';
+--------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for dba@%                                                                                                                         |
+--------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'dba'@'%' IDENTIFIED BY PASSWORD '*CAABA4CFB7E71E51477E0658FC2D2BBA1267E669' WITH MAX_USER_CONNECTIONS 10 |
+--------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

The documentation includes details that you can flush the resource limits, however I have found no way to monitor the current usage.

I welcome any feedback from the MySQL Community.

Monitoring MySQL Product Options

I’ve had plenty of comments on specific products to Monitoring MySQL Options before providing the completed list. Here are the results from my survey to give everybody a more complete list.

Nagios 25 xxxxxxxxxxxxxxxxxxxxxxxxx
MONyog 8 xxxxxxxx
Cacti 4 xxxx
Munin 3 xxx
MySQL Enterprise Monitor/Merlin 3 xxx
Hyperic 2 xx
KontrolBase 2 xx
Zabbix 2 xx
Big Brother 1 x
iGlass 1 x
MyDBA 1 x
MySQL AR 1 x
pacemaker 1 x
Panopta 1 x
Opsview 1 x
Monit 1 x
Tivoli 1 x

NOTE: Some answers included multiple products, these are all counted separately in the above figures.

There are a few products that are not listed at Monitoring MySQL in this list.

If you want to list what you use, please continue to use the MySQL Alert Monitoring Survey. Thanks to all those that replied.

Monitoring MySQL options

My recent poll What alert monitoring do you use? showed 25% of the 58 respondents to bravely state they had no MySQL monitoring. I see 1 in 3, ~33% in my consulting so this is consistent.


There is no excuse to not have some MySQL Monitoring on your production system. At the worse case, you should be logging important MySQL information for later analysis. I use my own Logging and Analyzing scripts on every client for an immediate assessment regardless of what’s available. I combine that with my modified statpack to give me immediate text based analysis, broken down by hour chunks for quick reference. These help me in troubleshooting, but they are not a complete solution.

The most popular options I see and are also reflected in the results are:

There is a good list, including some products I did not know. My goal is to get this information included in the Monitoring-MySQL information site.

I have some additional information on Cacti and MONyog, and I’ll be sharing this information in upcoming posts.

Unknown locale for statpack & maatkit

I had trouble today on a client site using my MySQL power tools Maatkit and Statpack.

$ ~/scripts/statpack.py --files=mysql.status.091015.080001.txt,mysql.status.091015.090001.txt
Traceback (most recent call last):
  File "/home/rbradfor/scripts/statpack.py", line 563, in ?
    main()
  File "/home/rbradfor/scripts/statpack.py", line 527, in main
    locale.setlocale(locale.LC_NUMERIC, '')
  File "/usr/lib64/python2.4/locale.py", line 381, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting
$ cat /var/log/slow-query.log | ./mk-query-digest
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
	LANGUAGE = (unset),
	LC_ALL = (unset),
	LANG = "e_US"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

I tracked a difference in the LANG environment variable with what is on another production server. Changing it addressed the problem, however I suspect a more underlying OS related problem that I did not have time to address.

$ env
...
LANG=e_US
...
$ export LANG=en_US.UTF-8

I didn’t track the source of e_US, en_US also worked.

Take a look at mk-query-digest

Q: What SQL is running on your MySQL database server now?
A: The bane of pain for MySQL DBA’s when there is no official MySQL instrumentation that is dynamic and fine grained sufficiently to solve this problem at the SQL interface.

While hybrid solutions exist, the lack of dynamic and real-time are the issues. There is however great work being done by Baron and others on Maatkit mk-query-digest and packet sniffing the MySQL TCP packets.

$ sudo tcpdump -i eth0 port 3306 -s 65535  -x -n -q -tttt | ./mk-query-digest --type tcpdump
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
# Caught SIGINT.
5444 packets captured
8254 packets received by filter
2809 packets dropped by kernel
# 2.1s user time, 40ms system time, 22.23M rss, 57.60M vsz
# Overall: 1.58k total, 38 unique, 262.67 QPS, 2.34x concurrency _________
#                    total     min     max     avg     95%  stddev  median
# Exec time            14s    41us      2s     9ms    23ms    72ms   236us
# Time range        2009-10-05 08:17:44.377926 to 2009-10-05 08:17:50.052460
# bytes            271.31k       8   8.79k  176.28  621.67  412.51   44.60
# Rows affe            248       0       3    0.16    0.99    0.38       0
# Warning c              0       0       0       0       0       0       0
#   3% (58)   No_index_used

# Query 1: 118.67 QPS, 1.23x concurrency, ID 0x16219655761820A2 at byte 2167682
#              pct   total     min     max     avg     95%  stddev  median
# Count         45     712
# Exec time     52      7s    41us      1s    10ms    23ms    80ms   138us
# Hosts                 11 10.251.199... (132), 10.251.103... (129)... 9 more
# Time range 2009-10-05 08:17:44.377926 to 2009-10-05 08:17:50.051177
# bytes          2   6.43k       8      17    9.25   16.81    3.15    7.70
# Errors                 1    none
# Rows affe      1       4       0       1    0.01       0    0.07       0
# Warning c      0       0       0       0       0       0       0       0
#   0% (1)    No_index_used
# Query_time distribution
#   1us
#  10us  ################################################
# 100us  ################################################################
#   1ms  #####
#  10ms  #############
# 100ms  #
#    1s  #
#  10s+
# EXPLAIN
select 1G

....

# Rank Query ID           Response time    Calls   R/Call     Item
# ==== ================== ================ ======= ========== ====
#    1 0x16219655761820A2     7.3861 54.9%     712   0.010374 SELECT
#    2 0x930DE584EC815E11     1.6664 12.4%      35   0.047611 SELECT X
#    3 0x68B1E4E47977667A     1.4265 10.6%      71   0.020092 SELECT Y Z
...

In this real-time example, the SELECT 1 a Connector/J keep alive in version 3.1.4 using iBATIS is the major SQL statement used. (yes MM I know about /* ping*/, have suggested to client). I was however with additional sample times able to identify a new query and confirm a full table scan by lack of good index. Monitoring had highlighted an increase in SQL statements and table scans, but you need tools such as this to identify the problem SQL in a well tuned system.

There is a lot of information to digest with this output, to confirm and determine the relative benefit of each number, the histogram etc, but the identification of SQL in real-time and the good work of overall summaries and comments for EXPLAIN and SHOW CREATE TABLE for example shows this tool has been designed by MySQL DBA’s for MySQL DBA’s.

Sheeri just wrote about Dynamic General and Slow Query Log Before MySQL 5.1 which apart from the File I/O overhead is an idea I’d not considered before. What may be a good idea, is to pass this information into a named pipe and then let another process do whatever. Drizzle solves this problem with query logging information being able to be shipped off to Gearman.

Simplicity

Simplicity – Always strive for a simpler solution.

This is a principle I have held and have used for many years in my technology based profession.

It’s very surprising that many organizations when addressing a problem forget to look at what is indeed right infront of them. The same is said about solving a technology problem. When I first heard about Agile Methodology practices in eXtreme Programming (XP) in 1999, I was quick to adopt this approach, because for no other words, it simplified the software development approach. It used a common sense, was practical and provided a test driven approach to improving quality which is key to successful software.

I was reading To Change Effectively, Change Just One Thing where Peter Bregman states “Just simplify it. Reduce it to its essence.” and ” The brilliance is rarely in the model, it’s in the implementation.” I’d encourage you to read the full article which has several valuable reference points.

The KISS – Keep it simple, stupid principle is something you should practice daily. Not just in your job, but in your life.

Looking just at the data

There are many areas you need to review when addressing MySQL performance such as current database load, executed SQL statements, connections, configuration parameters, memory usage, disk to memory ratio, hardware performance & bottlenecks just to name a few.

If you were to just look at the data that is held in the database, what would you consider?
Here are my tips, when looking just at the data.

  1. What is the current database size?
  2. What is the growth of data over time, say daily, weekly?
  3. Which are the 2 largest tables now?
  4. What 2 tables are growing the fastest?
  5. What tables have greatest churn, specifically DELETE’s?
  6. How often do you optimize your tables?
  7. What is your archiving/purging strategy? Do you even have one?
  8. Review data types? I average 25% reduction in footprints, just by choosing optimal data types, generally with zero code changes.
  9. What further data simplification can occur to reduce size, eg. INT for IP’s, enums, removing repeating text etc?
  10. What normalization of data can occur?
  11. What storage engines are in use?
  12. What data is write once data?
  13. Can data be stored in other forms, e.g. outside a relational database?

Even without looking at the SQL statements or the MySQL configuration you can generally deduce a lot of information about the application by just looking at the data.

What alert monitoring do you use?

More importantly, how often to you confirm access to your server and database with that alert monitoring?

With a client yesterday the primary database server while still usable and serving connections for a while, but was not accessible via SSH to investigate performance issues. It eventually became non responsive and required a physical reboot. With alert monitoring for system availability only recorded every 5 minutes this was simply too long a delay.

This lead to a discussion with more questions then answers including.

  • How often should you ping your server(s), both internally and externally?
  • How often do you connect physically to your server for confirmation, e.g. a ssh keyed authentication test?
  • How often do you perform a physical database connection test?
  • How often do you do an end to end test, including http request to database query test?

As with all of these, you also want to time these operations for any deviations.

I’ve created a very simple MySQL Alert Monitoring survey. I would appreciate your input.

NoSQL options

The NoSQL event in New York had a number of presentations on non relational technologies including of Hadoop, MongoDB and CouchDB.

Coming historically from a relational background of 20 years with Ingres, Oracle and MySQL I have been moving my focus towards non relational data store. The most obvious and well used today is memcached, a non persistent distributed key/value pair store. There are a number of persistent key/value stores in the marketplace, Tokyo Cabinet, Project Voldemort and Redis to name a few.

My list of data store products helps to identify the complex name space of varying products that now exist. A trend is towards schema less solutions, the ability to better manage dynamically typed/formatted information and the Agile Methodology release approach is simply non achievable in a statically type relational database table/column structure. The impact of constant ALTER TABLE commands in a MySQL database makes your production system unusable.

In a highly distribute online and increasing offline operation, fault tolerance and data synchronization and eventual consistency are required features in complex topologies such as multi-master.

I advise and promote a technology agnostic solution when possible. With the use of an API this is actually achievable, however in order to use a variety of backend data store products, one must consider the design patterns for optimal management. Two factors to support a highly distributed data set are no joins and minimal transactional semantics. The Facebook API is a great example, where there are no joins for their MySQL Relational backend. The movement back to a logical and non-normalized schema, or move towards a totally schemaless solution do require great though in the architectural concepts of your application.

Ultimately feature requirements will dictate the relative strengths and weaknesses of products. Full text search is a good example. CouchDB provides native support via Lucene. Another feature I like of couchDB is its append only data mode. This makes durability easy, and auto-recovery after crash a non issue, another feature a transactional relational database can not achieve.

With a 2 day no:sql(east) conference this month, there is definitely greater interest in this space.

Unexplained function output

I was asked today to confirm the operation of INET_ATON() and INET_NTOA() functions for converting IP4 strings to numeric representations. My tests on the machine I was just connected to at the very instant reported the following results.

mysql> SELECT VERSION();
+-----------------+
| VERSION()       |
+-----------------+
| 5.1.31-1ubuntu2 |
+-----------------+
1 row in set (0.00 sec)

mysql> SELECT INET_ATON('74.165.97.204') AS ipn;
+------------+
| ipn        |
+------------+
| 1252352460 |
+------------+
1 row in set (0.00 sec)

mysql> SELECT INET_NTOA(1252352460) as ipa;
+---------------+
| ipa           |
+---------------+
| 74.165.97.204 |
+---------------+
1 row in set (0.01 sec)

The results on the client via ODBC using MySQL 5.0.45 was?

ipn
1252352460

ipa
37342E3136352E39372E323034

What is causing this? It was immediately suspicious the pattern of 2E (the only letter), which translates from Hex to decimal to ‘.’ and 37 becomes 7 and 34 becomes 4, so the string is in hexidecimal and then with the UNHEX() function you get the right answer?

mysql> select unhex('37342E3136352E39372E323034');
+-------------------------------------+
| unhex('37342E3136352E39372E323034') |
+-------------------------------------+
| 74.165.97.204                       |
+-------------------------------------+

Could it be the ODBC drivers? Investigation showed them current as 5.01.05.00

Searching the MySQL Bugs database didn’t reveal anything noticable, nor on the forums.

My best suggestion was to post on the MySQL ODBC forums but I welcome any feedback from my readers.