Tee Filter

Overview

The tee filter is a "plumbing" fitting in the MariaDB MaxScale filter toolkit. It can be used in a filter pipeline of a service to make copies of requests from the client and send the copies to another service within MariaDB MaxScale.

Please Note: Starting with MaxScale 2.2.0, any client that connects to a service which uses a tee filter will require a grant for the loopback address, i.e. 127.0.0.1.

Configuration

The configuration block for the TEE filter requires the minimal filter parameters in its section within the MaxScale configuration file. The service to send the duplicates to must be defined.

[DataMartFilter]
type=filter
module=tee
target=DataMart

[Data-Service]
type=service
router=readconnroute
servers=server1
user=myuser
password=mypasswd
filters=DataMartFilter

Filter Parameters

The tee filter requires a mandatory parameter to define the service to replicate statements to and accepts a number of optional parameters.

target

The target where the filter will duplicate all queries. The target can be either a service or a server. The duplicate connection that is created to this target will be referred to as the "branch target" in this document.

service

The service where the filter will duplicate all queries. This parameter is deprecated in favor of the target parameter and will be removed in a future release. Both target and service cannot be defined.

match, exclude and options

These regular expression settings limit the queries replicated by the tee filter.

match=/insert.*into.*order*/
exclude=/select.*from.*t1/
options=case,extended

source

The optional source parameter defines an address that is used to match against the address from which the client connection to MariaDB MaxScale originates. Only sessions that originate from this address will be replicated.

source=127.0.0.1

user

The optional user parameter defines a user name that is used to match against the user from which the client connection to MariaDB MaxScale originates. Only sessions that are connected using this username are replicated.

user=john

sync

Enable synchronous routing mode. This boolean parameter was added in MaxScale 6.2.0 and is disabled by default.

When configured with sync=true, the filter will queue new queries until the response from both the main and the branch target has been received. This means that for n executed queries, n - 1 queries are guaranteed to be synchronized. Adding one extra statement (e.g. SELECT 1) to a batch of statements guarantees that all previous SQL statements have been successfully executed on both targets.

In the synchronous routing mode, a failure of the branch target will cause the client session to be closed.

Limitations

• All statements that are executed on the branch target are done in an asynchronous manner. This means that when the client receives the response there is no guarantee that the statement has completed on the branch target. The sync feature provides some synchronization guarantees that can be used to verify successful execution on both targets.

• Any errors on the branch target will cause the connection to it to be closed. If target is a service, it is up to the router to decide whether the connection is closed. For direct connections to servers, any network errors cause the connection to be closed. When the connection is closed, no new queries will be routed to the branch target.

With sync=true, a failure of the branch target will cause the whole session to be closed.

Module commands

Read Module Commands documentation for details about module commands.

The tee filter supports the following module commands.

tee disable [FILTER]

This command disables a tee filter instance. A disabled tee filter will not send any queries to the target service.

tee enable [FILTER]

Enable a disabled tee filter. This resumes the sending of queries to the target service.

Examples

Example 1 - Replicate all inserts into the orders table

Assume an order processing system that has a table called orders. You also have another database server, the datamart server, that requires all inserts into orders to be replicated to it. Deletes and updates are not, however, required.

Set up a service in MariaDB MaxScale, called Orders, to communicate with the order processing system with the tee filter applied to it. Also set up a service to talk to the datamart server, using the DataMart service. The tee filter would have as its service entry the DataMart service, by adding a match parameter of "insert into orders" would then result in all requests being sent to the order processing system, and insert statements that include the orders table being additionally sent to the datamart server.

[Orders]
type=service
router=readconnroute
servers=server1, server2, server3, server4
user=massi
password=6628C50E07CCE1F0392EDEEB9D1203F3
filters=ReplicateOrders

[ReplicateOrders]
type=filter
module=tee
target=DataMart
match=insert[   ]*into[     ]*orders

[DataMart]
type=service
router=readconnroute
servers=datamartserver
user=massi
password=6628C50E07CCE1F0392EDEEB9D1203F3
filters=QLA-DataMart

[QLA-DataMart]
type=filter
module=qlafilter
options=/var/log/DataMart/InsertsLog

[Orders-Listener]
type=listener
target=Orders
protocol=MariaDBClient
port=4011

[DataMart-Listener]
type=listener
target=DataMart
protocol=MariaDBClient
port=4012