Blue Lines and Gradients

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LSPE @Yahoo mysql-proxy

By Farhad Saberi
- Overview and architecture
- Making The case for a proxy
- Lua
- Lua examples
- The admin interface
- currently known issues
Overview and Architecture

Same idea as any other proxy. Sits between the
application and its Database:
Overview and Arhitecture
Read only Load Balancing with multiple
–proxy-read-only-backend-addresses option
Making The case for mysql-proxy

Easier sites management.

Hundreds of connection definitions use the
same host and port. DB Host connection
changes are done at one place only.

No need to restart for configuration or
behavioral changes. It all happens in real
time.
Making the case for mysql-proxy

Flexible, Powerful and invisible:

intercept, tokenize and modify queries

Deny/allow queries based on DB or DB User.

Deny/allow based on a regex

Construct your own results set and return it to
the application without ever actually querying
the backend database.

LUA embedded
Making the case for a proxy

It's fast and stable:

Small daemon, about 35 MB in VSZ compared
to a preforked apache child being 50 to 100
MB.

Coded in C

implements connection pooling

Doesn't need to do NS lookups every time

Has never “crashed” on me so far!
Making the case for mysql-proxy
Open source.
LUA

Simple scripting language

Small: its whole distribution fits in a floppy disk.

Extensible; it is easy to interface with C code.
LUA

Widely used in games:
LUA

Mysql-proxy is the application code and Lua is
its extension language. You change a running
mysql-proxy's behavior and variables in a single
Lua script in real time (no restart required).
Lua examples
Mysql-proxy starts with
–proxy-backend-addresses=db1.host.net, db2.host.net,
db3.host.net
Choose your backend in connect_server()
Function connect_server()
proxy.connection.backend_ndx=2
End
And you will always connect to db2.host.net.
If you change 2 to 3, you will always connect to db3.
Note: Lua's array starts at 1, !0
Lua examples
Deny all queries to any backend DB:
function read_query(packet)
if string.byte(packet) == proxy.COM_QUERY then
local fields = { } local rows = { }
fields = { { name = “message from DBA”,
type =proxy.MYSQL_TYPE_STRING}, }
rows[1] = { “maintenance”}
proxy.respose = { type = proxy.MYSQLD_PACKET_OK,
resultset = { fields = fields, rows = rows }
}
return proxy.PROXY_SEND_RESULT –means bypass backend, return to client now
end
end
Lua examples
For any query issued, this will be the result:
mysql> show tables; # or anything else
+--------------------------+
| message from DBA |
+--------------------------+
| maintenance
|
+---------------------------+
Lua example
denying access to just one table using a regex. Return mysql error msg to client.
Function read_query(packet)
if packet:byte() == proxy.COM_QUERY then
local query= packet:sub(2)
print (“query: “ .. query) – debugging purpose
if string.match(query:lower(), “from%s+.*my_table”) then
proxy.response.type = proxy.MYSQLD_PACKET_ERR
proxy.response.errmsg = “access denied to table my_table”
return proxy.PROXY_SEND_RESULT
end
end
end
Lua example
Running any query that would match “from%s+.* my_table”
will return
ERROR 1105 (07000): access denied to table my_table
Lua example
Some other things you can do:



Start/stop mysqld backend.
Choose your backend DB based on which IP
address, or which mysql user the client has.
Modify result set by adding or removing a
column from the returned table.

Time your queries. Gather statistics.

Your limits are that of the Lua language.
The admin interface


You can monitor and show internal structures of the
running mysql-proxy process by programming your own
admin interface in Lua.
Start mysql-proxy with admin options:
--admin-address=127.0.0.1:10008
--admin-username=root
–admin-password=password
--admin-lua-script=/mysql-proxy/share/admin/admin.lua
The admin interface
Function read_query(packet)
If packet:byte() ~= proxy.COM_QUERY
then return_error(“[admin] we only handle COM_QUERY”); --user defined
end
Local rows = { } local fields = { } – no need for a semicolon in Lua
if packet:sub(2) == “ls” then
– if query is an ls
fields = {
{ name = “backend_ndx”, type = proxy.MYSQL_TYPE_LONG },
{ name = “address” , type = proxy.MYSQL_TYPE_STRING } ,
{ name = “connected_clients”, type = proxy.MYSQL_TYPE_LONG},
}
for i = 1, #proxy.global.backends do
Local b = proxy.global.backends[i]
rows[#rows + 1] = {
i, b.dst.name, b.connected_clients
}
end
end
… Now build proxy.response and return with proxy.PROXY_SEND_RESULT
The admin interface
Querying the previously Lua coded interface will return:
mysql>msyql -u root -ppassword -h 127.0.0.1 -P 10008
mysql> ls;
+------------------+--------------------------+-------------------------+
| backend_ndx | address
| connected_clients |
+------------------+--------------------------+-------------------------+
|
1 | 192.168.1.9:3309 |
23 |
+------------------+--------------------------+-------------------------+
|
2 | 192.168.1.10:3309 |
142 |
+------------------+--------------------------+-------------------------+
Currently known issues



Read/Write splitting does not work if used by
more than one client on the same proxy
process. This is a known issue and I'm
assuming it is being worked on.
A bit complicated. Everything has to be coded
by you.
You need to know Lua well. (not a bad thing
though)
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