Wednesday, June 22, 2011

Less known facts about MySQL user grants

Reading MySQL security: inconsistencies I remembered a few related experiments that I did several years ago when I was studying for the MySQL certification. The first fact that came to mind is about the clause "WITH GRANT OPTION", which can only be given on the full set of options, not on a single grant. For example
GRANT INSERT,DELETE,UPDATE on world.* to myuser identified by 'mypass';
GRANT SELECT on world.* to myuser identified by 'mypass' WITH GRANT OPTION;
show grants for myuser\G
*************************** 1. row ***************************
Grants for myuser@%: GRANT USAGE ON *.* TO 'myuser'@'%' IDENTIFIED BY PASSWORD '*6C8989366EAF75BB670AD8EA7A7FC1176A95CEF4'
*************************** 2. row ***************************
Grants for myuser@%: GRANT SELECT, INSERT, UPDATE, DELETE ON `world`.* TO 'myuser'@'%' WITH GRANT OPTION
If you are surprised about the "WITH GRANT OPTION" clause applying to all grants instead of only applying to the SELECT, you forgot to consider how the grants are stored. All the grants for a given user (and a user is the combination of a name and a provenience) are stored in a single record in the mysql.user table. The GRANT OPTION is a column in that record. It is either set or not. You can't assign this option for only one attribute in the same record. It's either all the flagged grants or nothing. If you want to assign the "with grant option" on a single column, you must change either the provenience or the name of the user (thus opening another record). But also this addition may not be enough to reach your goal, as you can see in the next section. The other fact that came to mind about the "WITH GRANT OPTION" clause is that, in the examples given, it is ineffective. I dare say illusory. Let's start. As root user, we create this user:
root> grant all on granted.* to grantee identified by 'happyuser' with grant option;
The granted database exists, and now we have an user that can modify it, and, we think, delegate some functions to someone else.
grantee> grant select on granted.* to delegated identified by 'happy';
ERROR 1410 (42000): You are not allowed to create a user with GRANT
grantee> create user delegated;
ERROR 1227 (42000): Access denied; you need (at least one of) the CREATE USER privilege(s) for this operation
Right. I can't create a new user, but only transfer my superpowers to someone else. I will ask root to create the user, and then I will give it another try.
root>  create user delegated;
Query OK, 0 rows affected (0.00 sec)

grantee> grant select on granted.* to delegated identified by 'happy';
ERROR 1044 (42000): Access denied for user 'grantee'@'%' to database 'mysql'
Ouch! Since the grant tables are in the 'mysql' database, I don't have access. I will ask root to give me access to the mysql 'user' and 'db' tables.
root>  grant insert on mysql.user to grantee ;
Query OK, 0 rows affected (0.00 sec)
root>  grant insert on mysql.db to grantee ;
Query OK, 0 rows affected (0.00 sec)

grantee> grant select on granted.* to delegated identified by 'happy';
ERROR 1044 (42000): Access denied for user 'grantee'@'%' to database 'mysql'
Not good. I tried then to get SELECT,INSERT,UPDATE,DELETE for all the grant tables inside 'mysql'. Still, I could not exercise my grant options. Finally, the only solution was to get privilegs on the whole mysql database.
root> grant insert,select,delete,update on mysql.* to grantee;
Query OK, 0 rows affected (0.00 sec)

grantee> grant select on granted.* to delegated identified by 'happy';
Query OK, 0 rows affected (0.00 sec)
At last, I can grant something to someone.
But wait! Now that I can modify the 'mysql' database ...perhaps I could ...
grantee> update user set Select_priv ='Y',
 Insert_priv ='Y', Update_priv ='Y', Delete_priv ='Y',
 Create_priv ='Y', Drop_priv ='Y', Reload_priv ='Y',
 Shutdown_priv ='Y', Process_priv ='Y', File_priv ='Y',
 Grant_priv ='Y', References_priv ='Y', Index_priv ='Y',
 Alter_priv ='Y', Show_db_priv ='Y', Super_priv ='Y',
 Create_tmp_table_priv ='Y', Lock_tables_priv ='Y', Execute_priv ='Y',
 Repl_slave_priv ='Y', Repl_client_priv ='Y', Create_view_priv ='Y',
 Show_view_priv ='Y', Create_routine_priv ='Y', Alter_routine_priv ='Y',
 Create_user_priv ='Y', Event_priv ='Y', Trigger_priv ='Y',
 Create_tablespace_priv ='Y' where user = 'grantee';
This does not enhance my current grants, because I don't have the SUPER privilege (yet), but I can wait until the server restarts or until someone issues a 'flush privileges'. An then I will have full access to the server. Obviously, this situation is not what the DBA had in mind when the user 'grantee' was created.

Update The habit of always seeing the password set as integral part of the GRANT command has made me err on judgment.
As noted in one of the comments, the "grantee" user could have granted privileges to "delegated" without assigning a password. In this case,"grantee" does not need separate grants to the mysql database, which were apparently needed only if you wanted to set the password with the GRANT command.
All the above post is a miscalculation. The additional grants are not needed, provided that you don't include a password clause in your GRANT command.

Monday, June 20, 2011

Introducing the Tungsten-toolbox

tungsten toolbox white After the public home for Tungsten Replicator, we needed another place where to host complementary tools. We discussed the pros and cons of hosting these tools in the same place where we publish Tungsten, but in the end we decided that it's more practical to have a separate project, where we can publish tools related to database replication, no matter if they are dedicated to Tungsten or if they can work with other replication systems. So, here it is. We have now Tungsten Toolbox, a site where we will collect our tools and accept contributions from others.
We have already a few tools that, after being cleaned up, will find their way to this repository. The one that was more or less ready for prime time is the Tungsten Sandbox, a tool that installs more than one Tungsten instance with a backend database in the same host. It is, as you can imagine, based on the MySQL Sandbox and it works reasonably well. All the tools in this toolbox are released under the New BSD License. What can you expect to see in the near future? We have a few ideas already:
  • A binary log analyzer
  • A tool that changes properties on-the-fly
  • A JSON API for Tungsten
  • Sandboxes and deployers for complex topologies (multiple masters, fan-in)
  • Sandboxes and deployers for direct slaves
  • Deployers for a mix of MySQL native and Tungsten replication
  • A PostgreSQL sandbox
We are, of course, open to contributions. If you have a tool that is useful for database replication and want to release it under a BSD license, feel free to propose it in the Google Group discussion on Tungsten Replicator.

Tuesday, June 14, 2011

What happened to MySQL Forge?

Update
Soon after I posted this article, the Forge came back online! Thanks!


MySQL Forge has been offline for two days now. (2011-06-14) No sign of acknowledgement of this problem from the MySQL team. What is happening? For those not well acquainted with MySQL Forge, here are the facts. The MySQL Forge is a site that was intended to contain all community contributions. The reality did not follow the plans very closely, and some sections of the forge ended up with less contents than what should be useful. However, there are a few sections of the forge that are extremely useful to users:
  • The Wiki, which is full of irreplaceable documentation, such as the MySQL internals, description of preview features, slides and recordings of MySQL University, manual of many tools (such as the Random Query Generator, and more
  • The worklogs, or the blueprints for most MySQL features, past, present, and future
  • The tools/snippets, which is a collection of community contributed scripts. Not many, but most of them of high quality and quite useful.
I know that there was a lot of spam in the forge, but I really hope that it was taken off line on purpose. If its maintenance is a problem, I am sure we can find plenty of volunteers in the community that want to host the wiki and the rest of the useful stuff. Hello? Anybody there at Oracle/MySQL? Please give us back the forge. Thanks.

Thursday, June 09, 2011

Getting started with Tungsten Replicator and Tungsten Sandbox

We have been busy, at Continuent. In addition to our usual work with high performance replication, we have addressed usability issues, since we know that a hard-to-use problem, no matter how powerful, has low adoption. Thus, is with some personal satisfaction that I can announce the release of Tungsten Replicator 2.0.3, which comes with several huge improvements in matter of user friendliness. The new installation procedure is so user friendly, in fact, that I was able to build a sophisticated tungsten-sandbox with a 150-line shell script. (The corresponding features for MySQL Sandbox required 4,500 lines of Perl).
Enough self celebration, though. Let's get started, as the title of this post suggests, with the practical steps.

Requirements

Before we begin, there are a few requirements to meet.
  1. You need to be on a Unix-like operating system. Our main choice is Linux. If you want to test on Mac OSX, it works, but we won't recommend it.
  2. Java JRE must be installed. And it must be the original one, not the Open JDK. Update: The requirement against OpenJDK has been lifted. It works fine in my tests.
  3. Ruby 1.8 must be installed. This is mainly needed during the installation phase only, but it is required nonetheless.
  4. The user account that will install and run Tungsten must have ssh access to the other hosts involved in the cluster
  5. The above mentioned user must have sudo access. This is only needed if you want to use Tungsten Replicator to run backups that involve root access (like xtrabackup). We may lift this requirement later, but for now you need to enable it, at least during the installation, and remove the access when you are done.
  6. This user must also have read access to MySQL binary logs. Usually you achieve this by making sure that the binary logs are readable by users belonging to the "mysql" group, and by adding such group to your user.
  7. There must be a MySQL users for Tungsten replication. This user must have full access to the database server, with grant option.
  8. The MySQL server must have binary logging enabled.
  9. If you have MySQL native replication running, you must stop it.

Getting the code and install

The code is released in the downloads section of Tungsten's home. The current recommended version is 2.0.3, but if you like to be really up to date, we also publish a list of recent builds from our build server, which you can use to have a go at the replicator. For this simple installation, I will use four servers from our server farm. The servers are named R1, R2, R3, and R4. The first good news of the new installation process is this: you need to install in one server only!. More details follow. First off, create a directory where you want to install. Use a non-root account. Just make sure that it's the same user in all the servers, and that such user can access the directory where you want to install. I am going to call this directory planet.
cd $HOME
for N in 1 2 3 4 ; do ssh r$N mkdir planet ; done
cd planet 
wget http://tungsten-replicator.googlecode.com/files/tungsten-replicator-2.0.3.tar.gz
tar -xzf tungsten-replicator-2.0.3.tar.gz
cd tungsten-replicator-2.0.3
I have already a MySQL user named tungsten with password "mypwd" (but it can be anything you like, as long as it has the required privileges). Now we have all the components. If you have read the Tungsten documentation, please ignore the ./configure script. That is left for compatibility reasons, and will be deprecated soon. Instead, to install the cluster of our 4 servers, let's do the following:
export TUNGSTEN_BASE=$HOME/planet

./tools/tungsten-installer \
    --master-slave \
    --master-host=r1 \
    --datasource-user=tungsten \
    --datasource-password=mypwd \
    --service-name=dragon \
    --home-directory=$TUNGSTEN_BASE \
    --cluster-hosts=r1,r2,r3,r4 \
    --start
Some comment on this command: --master-slave is the installation mode (see below for more info). --service-name can be anything you want. --home-directory is where all the installation sub directories will go. --cluster-hosts is the list of servers you want to install, and finally, --master-host is the host that will be installed as a master, while all the others will be slaves of that one. If you have followed the instructions carefully, the installer will bring up the Tungsten cluster without any fuss, Unix style. If you hate silent installations, you can get the full monty by adding some options:
./tools/tungsten-installer \
    --verbose \
    --master-slave \
    --master-host=r1 \
    --datasource-user=tungsten \
    --datasource-password=mypwd \
    --service-name=dragon \
    --home-directory=$TUNGSTEN_BASE \
    --cluster-hosts=r1,r2,r3,r4 \
    --start-and-report
If you run the installer in verbose mode, you will see an extremely long list of validation checks that the installed does on your current servers and on the ones that are listed in the --cluster-hosts option. If everything went well, you will find the following directories in $HOME/planet (for all servers in your cluster):
  • configs, containing the configuration file created by the installer. This file describes your cluster
  • releases, containing the Tungsten binaries.
  • thl, containing Tungsten's Transaction History Logs. These logs are like MySQL binary logs, but with much more metadata, including a global transaction ID, which is missing in MySQL native replication.
  • relay, which should be empty, unless you install in "direct" mode (see below.)
  • tungsten, which is a symlink to the Tungsten directory inside releases.
In addition to the above mentioned directories, Tungsten Replicator creates a database for each service. Since we have only one service in this topology, you will find a database named "tungsten_dragon". (If you have called your service "bunny", you will instead find "tungsten_bunny"). Inside this database there is the replication metadata necessary for making the servers fault tolerant. Only a small amount of data is kept on that database. It's roughly corresponding to what you get from the .info files in MySQL native replication. To test that the system is OK, let's find our tools. The first one is trepctl, which, among other things, can give us an overview of the running services.
cd $HOME/planet
./tungsten/tungsten-replicator/bin/trepctl services
Processing services command...
NAME              VALUE
----              -----
appliedLastSeqno: 0
appliedLatency  : 1.152
role            : slave
serviceName     : dragon
serviceType     : local
started         : true
state           : ONLINE
Finished services command...

./tungsten/tungsten-replicator/bin/trepctl -host r1 services
Processing services command...
NAME              VALUE
----              -----
appliedLastSeqno: 0
appliedLatency  : 0.936
role            : master
serviceName     : dragon
serviceType     : local
started         : true
state           : ONLINE
Finished services command...

mysql -h r1 -e 'create schema if not exists test'
mysql -h r1 -e 'create table test.t1 (i int)'

./tungsten/tungsten-replicator/bin/trepctl services
Processing services command...
NAME              VALUE
----              -----
appliedLastSeqno: 2
appliedLatency  : 0.155
role            : slave
serviceName     : dragon
serviceType     : local
started         : true
state           : ONLINE
Finished services command...

./tungsten/tungsten-replicator/bin/trepctl -host r1 services
Processing services command...
NAME              VALUE
----              -----
appliedLastSeqno: 2
appliedLatency  : 0.044
role            : master
serviceName     : dragon
serviceType     : local
started         : true
state           : ONLINE
Finished services command...
After the installation, trepctl reported the last applied sequence number (appliedLastSeqno) as 0. Following the execution of two commands in the master, such number became 2. If you want to know more of what was happening, you can use the thl command. This corresponds roughly to using mysqlbinlog with MySQL native replication logs.
/tungsten/tungsten-replicator/bin/thl -service dragon list |less
SEQ# = 1 / FRAG# = 0 (last frag)
- TIME = 2011-06-09 14:51:23.0
- EVENTID = 000002:0000000000000514;197609
- SOURCEID = qa.r1.continuent.com
- STATUS = COMPLETED(2)
- METADATA = [mysql_server_id=10;service=dragon;shard=test]
- TYPE = com.continuent.tungsten.replicator.event.ReplDBMSEvent
- OPTIONS = [##charset = ISO8859_1, createOrDropDB = , autocommit = 1, sql_auto_is_null = 1, foreign_key_checks = 1, unique_checks = 1, sql_mode = '', character_set_client = 8, collation_connection = 8, collation_server = 8]
- SQL(0) = create schema if not exists test /* ___SERVICE___ = [dragon] */
SEQ# = 2 / FRAG# = 0 (last frag)
- TIME = 2011-06-09 14:51:30.0
- EVENTID = 000002:0000000000000601;197610
- SOURCEID = qa.r1.continuent.com
- STATUS = COMPLETED(2)
- METADATA = [mysql_server_id=10;service=dragon;shard=test]
- TYPE = com.continuent.tungsten.replicator.event.ReplDBMSEvent
- OPTIONS = [##charset = ISO8859_1, autocommit = 1, sql_auto_is_null = 1, foreign_key_checks = 1, unique_checks = 1, sql_mode = '', character_set_client = 8, collation_connection = 8, collation_server = 8]
- SCHEMA = 
- SQL(0) = create table test.t1 (i int) /* ___SERVICE___ = [dragon] */
Once we are satisfied that replication is working, we can clean up the cluster and try other installation experiments. To clean up a cluster, you need to do the following:
  1. stop the replicator in all servers.
    for N in 1 2 3 4; do $PWD/tungsten/tungsten-replicator/bin/replicator stop; done
  2. remove the thl files from all servers.
  3. remove the tungsten_SERVICE_NAME database from all mysql servers
  4. run a "reset master" in the master database
  5. remove the directories created by the installer in all servers

Installation types

The procedure described above was, until a few months ago, the only thing you could do with Tungsten. Now you can broaden your horizons with a wider range of possibilities.

Master/slave is of course the main option, and it's the one that you have seen in the previous section. This method gives you the full set of Tungsten features and performance. It is the recommended method for production use and for benchmarking. In this scenario, the Tungsten replicator on the master will extract transactions from the binary log, transfer them to the THL, and share it with the slaves. The slaves will read from the THL and apply the transactions to the database. There are a few steps more in between, but for the sake of brevity I will skip them You can have a look at Robert Hodges blog for more info.
Slave "direct" is the alternative that you can use in production, and it's been designed to satisfy users who only want some particular benefits on the slave side, and don't care about global transaction IDs. If you are looking at parallel apply, this is probably a setup that you want to try. In this scenario, there is no replicator on the master. The slave pulls data remotely from the binary logs, copies them locally, and extracts data to the THL. Here's an example of how to start a slave-direct system:
./tools/tungsten-installer \
    --direct \
    --master-host=r1 \
    --slave-host=r4 \
    --master-user=tungsten \
    --slave-user=tungsten \
    --master-password=secret \
    --slave-password=secret \
    --service-name=Castor \
    --thl-port=21124 \
    --rmi-port=10104 \
    --channels=5 \
    --home-directory=$TUNGSTEN_BASE \
    --start-and-report

If your purpose is testing Tungsten, probably the Tungsten Sandbox is what you should try. This system is based on MySQL Sandbox, a framework that lets you install more than one MySQL server in the same host. Building on top of MySQL Sandbox, and leveraging the new flexibility in Tungsten installer, tungsten-sandbox allows you to build a master/slave system inside a single host. Let's give it a try. You need to have MySQL Sandbox installed, and at least one MySQL tarball expanded under $HOME/opt/mysql/X.X.XX (where X.X.XX is the MySQL version, such as 5.5.12).
cd $HOME/planet
mkdir sb
cd tungsten-replicator-2.0.3
wget http://tungsten-replicator.googlecode.com/files/tungsten-sandbox
./tungsten-sandbox -h
USAGE: ./tungsten-sandbox [flags] args
flags:
  -n,--nodes:  how many nodes to install (default: 3)
  -m,--mysql_version:  which MySQL version to use (default: '5.1.56')
  -t,--tungsten_base:  where to install the sandbox (default: '/home/tungsten/tsb2')
  -d,--group_dir:  sandbox group directory name (default: 'tr_dbs')
  -s,--service:  how the service is named (default: 'tsandbox')
  -P,--base_port:  port base for MySQL sandbox nodes (default: 710)
  -l,--thl_port:  port for the THL service (default: 1211)
  -r,--rmi_port:  port for the RMI service (default: 1010)
  -v,--[no]version:  show Tungsten sandbox version (default: false)
  -h,--[no]help:  show Tungsten sandbox help (default: false)
In my server, I have already expanded MySQL 5.5.10, and I want to install inside $HOME/tsb. So, here is what I do:
./tungsten-sandbox -m 5.5.10 -t ~/tsb
This command installs three instances of MySQL under $HOME/sandboxes and three of Tungsten under $HOME/tsb. Inside this directory, in addition to the running instances, we find some more goodies:
  • clear_all send_kill_all start_all status_all stop_all use_all : symlinks to the corresponding commands in MySQL sandbox
  • db1 db2 db3: these are the tungsten instances.
  • n1 n2 n3: quick links to access each MySQL node
  • replicator_all trepctl_all: utilities that run "replicator" or "trepctl" for each node with the arguments provided on the command line
Additionally, there are a few scripts inside each Tungsten instance in the sandbox:
  • trepctl: a link to the deep down trepctl
  • thl: a link to the thl utility
  • show_log: a quick way of showing the replicator log
Since this is a tool for testing, removing it is going to be easy.
~/tsb/replicator_all stop
~/tsb/clear_all
rm -rf ~/tsb/*

A final method of installing is a sandbox with ths slave-direct method. There is no dedicated script for this method, but thanks to the new installer, you can get the job done quite easily:
export NODE_OPTIONS='-c innodb_flush_log_at_trx_commit=2 -c max_allowed_packet=48M'
make_multiple_sandbox --group_directory=tr_dbs --sandbox_base_port=7100 5.5.10

TUNGSTEN_BASE=$HOME/tinstall/tsb/
./tools/tungsten-installer \
    --direct \
    --master-host=127.0.0.1 \
    --master-port=7101 \
    --slave-host=db2 \
    --slave-port=7102 \
    --master-user=root \
    --slave-user=root \
    --master-password=msandbox \
    --slave-password=msandbox \
    --master-log-directory=$HOME/sandboxes/tr_dbs/node1/data \
    --service-name=Castor \
    --thl-port=12112 \
    --channels=5 \
    --rmi-port=20000 \
    --home-directory=$TUNGSTEN_BASE \

./tools/tungsten-installer \
    --direct \
    --master-host=127.0.0.1 \
    --master-port=7101 \
    --slave-host=db3 \
    --slave-port=7103 \
    --master-user=root \
    --slave-user=root \
    --master-password=msandbox \
    --slave-password=msandbox \
    --master-log-directory=$HOME/sandboxes/tr_dbs/node1/data \
    --service-name=Pollux \
    --thl-port=22112 \
    --channels=1 \
    --rmi-port=20000 \
    --home-directory=$TUNGSTEN_BASE \
    --relay-directory=$TUNGSTEN_BASE/relay --start-and-report
This script creates two services (Castor and Pollux), with only one instance of Tungsten replicator, with all the servers (MySQL and Tungsten ones) in the same host.

Conclusions

There should be much more to say, but I will leave it for the coming days. In the meantime, I encourage everyone to try the new Tungsten and submit bug reports when things don't work as expected. As always, happy hacking!
P.S. Today at 10am PT there is a webinar on this very topic!

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