SmartRouter is the query router of the SmartQuery framework. Based on the type of the query, each query is routed to the server or cluster that can best handle it.
For workloads where both transactional and analytical queries are needed, SmartRouter unites the Transactional (OLTP) and Analytical (OLAP) workloads into a single entry point in MaxScale. This allows a MaxScale client to freely mix transactional and analytical queries using the same connection. This is known as Hybrid Transactional and Analytical Processing, HTAP.
SmartRouter is configured as a service that either routes to other MaxScale routers or plain servers. Although one can configure SmartRouter to use a plain server directly, we refer to the configured "servers" as clusters.
For details about the standard service parameters, refer to the Configuration Guide.
One of the clusters must be designated as the
master. All writes go to the
master cluster, which for all practical purposes should be a master-slave
ReadWriteSplit. This document does not go into details about setting up
master-slave clusters, but suffice to say, that when setting up the ColumnStore
servers they should be configured to be slaves of a MariaDB server running an
InnoDB engine. The ReadWriteSplit documentation has more on
Service as a Server
Currently the configuration for a router (service) can have a number of servers, but not other routers (services). Suppose you have a cluster of servers that are managed by ReadWriteSplit. In order for that cluster to be routed-to by SmartRouter, the service must be exposed as a server. A server section in the configuration file that exposes a service instead of defining an actual server, is known as Service as a Server.
Suppose we have a service like
[RWS-Row] type=service router=readwritesplit
for which we have defined the listener
[RWS-Row-Listener] type=listener service=RWS-Row socket=/tmp/rws-row.sock
That is, that service can be accessed using the socket
A server section that would expose that service as a server, looks like this:
[RWS-Row-as-a-server] type=server socket=/tmp/rws-row.sock
Assuming we have defined
RWS-Column-as-a-server similarly, we can define the SmartQuery
service as follows:
[SmartQuery] type = service router = smartrouter servers = RWS-Row-as-a-server, RWS-Column-as-a-server master = RWS-Row-as-a-server user = <user> password = <password> [SmartQuery-Listener] type = listener service = SmartQuery protocol = mariadbclient port = <port>
Note that the SmartQuery listener listens on a port, while the Service as a Server listeners listen on a Unix domain socket. The reason is that there is a significant performance benefit when SmartRouter accesses the services over a Unix domain socket compared to accessing them over a TCP/IP socket.
Note that RWS-Row-as-a-server is designated as the master.
The RWS-Row-as-a-server looks like this:
[RWS-Row-Listener] type = listener service = RWS-Row protocol = mariadbclient socket = /tmp/rws-row.sock [RWS-Row-as-a-server] type = server socket = /tmp/rws-row.sock protocol = MariaDBBackend
A complete configuration example can be found at the end of this document.
Cluster selection - how queries are routed
SmartRouter keeps track of the performance, or the execution time, of queries to the clusters. Measurements are stored with the canonical of a query as the key. The canonical of a query is the sql with all user-defined constants replaced with question marks. When SmartRouter sees a read-query whose canonical has not been seen before, it will send the query to all clusters. The first response from a cluster will designate that cluster as the best one for that canonical. Also, when the first response is received, the other queries are cancelled. The response is sent to the client once all clusters have responded to the query or the cancel.
There is obviously overhead when a new canonical is seen. This means that queries after a MaxScale start will be slightly slower than normal. The execution time of a query depends on the database engine, and on the contents of the tables being queried. As a result, MaxScale will periodically re-measure queries.
The performance behavior of queries under dynamic conditions, and their effect on different storage engines is being studied at MariaDB. As we learn more, we will be able to better categorize queries and move that knowledge into SmartRouter.
LOAD DATA LOCAL INFILEis not supported.
- The performance data is not persisted. The measurements have to be performed anew after each startup.
Complete configuration example
[maxscale] [row_server_1] type = server address = <ip> port = <port> protocol = MariaDBBackend [row_server_2] type = server address = <ip> port = <port> protocol = MariaDBBackend [Row-Monitor] type = monitor module = mariadbmon servers = row_server_1, row_server_2 user = <user> password = <password> monitor_interval = 2000ms [column_server_1] type = server address = <ip> port = <port> protocol = MariaDBBackend [Column-Monitor] type = monitor module = csmon servers = column_server_1 user = <user> password = <password> monitor_interval = 2000ms # Row Read write split [RWS-Row] type = service router = readwritesplit servers = row_server_1, row_server_2 user = <user> password = <password> [RWS-Row-Listener] type = listener service = RWS-Row protocol = mariadbclient socket = /tmp/rws-row.sock # Columnstore Read write split [RWS-Column] type = service router = readwritesplit servers = column_server_1 user = <user> password = <password> [RWS-Column-Listener] type = listener service = RWS-Column protocol = mariadbclient socket = /tmp/rws-col.sock [RWS-Row-as-a-server] type = server socket = /tmp/rws-row.sock protocol = MariaDBBackend [RWS-Column-as-a-server] type = server socket = /tmp/rws-col.sock protocol = MariaDBBackend # Smart Query router [SmartQuery] type = service router = smartrouter servers = RWS-Row-as-a-server, RWS-Column-as-a-server master = RWS-Row-as-a-server user = <user> password = <password> [SmartQuery-Listener] type = listener service = SmartQuery protocol = mariadbclient port = <port>