How do I configure connection pooling in ProxySQL ?

The variable has been documented here : mysql-free_connections_pct

More information with examples : Connection pooling

How does ProxySQL handle the USE dbname Command ?

Some user has raised a question asking why will USE database always succeed in ProxySQL even when the database doesn’t exist.

This document will explain how ProxySQL deals with default schema and -D [dbname] : USE databasename

Monitor module responsibilities in more details

The core of ProxySQL also observes the success/failure of backend servers, but it has some limitations (More details later on)

But the Monitor module extends the functionality of the core of ProxySQL.

How to configure monitoring in ProxySQL: Configure Monitoring

The responsibilities have also been documented: here

More in detail : click here

How does ProxySQL handle database failover?

An important point to note is that ProxySQL is an agent and it doesn’t handle any kind of failover by its own.
But it is developed to handle DB failovers initiated by external tools.

The below documents will explain how ProxySQL deals with failover to achieve high availability.

ProxySQL + MHA ProxySQL and MHA integration

ProxySQL + mysqlrpladmin ProxySQL and mysqlrpladmin

How to configure MHA Setup MHA

How do we avoid the problem of ProxySQL being a single point of failure?

ProxySQL itself doesn’t have a built-in HA solution, but it is very easy to architecture its deployment in order to avoid SPOF.
A few months back Percona published some articles where it is highlighted how to avoid single points of failure.

http://proxysql.com/blog/multiple-proxysql-on-same-ports

http://proxysql.com/blog/how-to-run-multiple-proxysql-instances

https://www.percona.com/blog/2017/01/19/setup-proxysql-for-high-availability-not-single-point-failure/

https://www.percona.com/blog/2016/09/16/consul-proxysql-mysql-ha/

Few more examples on how to implement MySQL HA (high-availability) solutions: here

What is Mirroring in ProxySQL and when to use it ?

ProxySQL’s mirror feature allows us to send real application traffic to a completely separate server without touching the application.
Mirroring functionality is not like replication topology in MySQL, but it has some use cases.

For more information: In detail

How to use flagIN, flagOUT, apply to improve performance if you have multiple query rules?

If you have more query rules, then all your queries have to match against all of them and this has a serious impact on performance. How can we avoid that?

flagIN, flagOUT, apply – They work together and apply logic into your rules so that even if you have more rules, you will get better performance.

flagIN, flagOUT, apply – these allow us to create a “chain of rules” that get applied one after the other. An input flag
value is set to 0, and only rules with flagIN=0 are considered at the beginning. When a matching rule is found for a
specific query, flagOUT is evaluated and if NOT NULL the query will be flagged with the specified flag in flagOUT. If
flagOUT differs from flagIN, the query will exit the current chain and enter a new chain of rules having flagIN as the
new input flag. If flagOUT matches flagIN, the query will be re-evaluated again against the first rule with said flagIN.
This happens until there are no more matching rules, or apply is set to 1 (which means this is the last rule to be
applied).

Benchmark Result : Too many query rules

How to create a chain of rules : example

Is there any monitoring tool available to get statistic report for ProxySQL servers?

Yes, use Grafana and the built-in ProxySQL Prometheus Exporter, read this blog to find out more and make sure to check the sample dashboards as well as a Docker based deployment available here.

How to manage ProxySQL configuration across multiple servers?

Actually it is easy to reconfigure ProxySQL at runtime , we can use a variety of approaches, like using a configuration management tool (Puppet, Chef, Ansible, Salt etc..) or a service discovery toos (Consul, Etcd, Zookeeper) to automatically reconfigure ProxySQL if needed.

The most convenient method is to use the native feature of ProxySQL Cluster

How to gracefully shutdown the ProxySQL process?

To kill is the right way for graceful shutdown of ProxySQL, the rest is handled internally. When executing the kill command, a SIGTERM signal is sent to the ProxySQL process.

SIGTERM 15 – Software termination signal (sent by kill by default)

More details : click here

No Hostgroup 0 has been configured, then why do we get “Max connect timeout reached while reaching hostgroup 0 after 10000ms”?

This is how MySQL Query Rules work while selecting hostgroups.

  1. When you set any query rules inside table mysql_query_rules, then your query gets analyzed by the Query Processor to decide which destination hostgroup it should be forwarded to. (according to mysql_query_rules.destination_hostgroup)
  2. When your Query Processor doesn’t find any query matching the query rule then the default hostgroup for the specific user is applied (according to mysql_users.default_hostgroup)

Example : Default Hostgroup for User

What is Multiplexing and How does it work (enable/disable)?

Multiplexing – Reduce the number of connections against mysqld, see detailed info here.

Many clients connections (tens of thousands) can use few backend connections (few hundreds).
So it is possible for the requests coming from a single client to be evenly distributed among all the backends of the same hostgroup.

ProxySQL understands the requirement of transactions execution.
If a transaction is running, then multiplexing is disabled until the transaction completes, either through a rollback or commit.
So ProxySQL will ensure that the statements within a transaction execute on same backend server by default.

Default value for mysql-multiplexing is true

mysql> select * from global_variables where variable_name like '%multiplexing%';
+--------------------+----------------+
| variable_name      | variable_value |
+--------------------+----------------+
| mysql-multiplexing | true           |
+--------------------+----------------+
1 row in set (0.01 sec)

More on multiplexing : Here

How to configure ProxySQL using the config file?

Yes, the option is available to start ProxySQL from the config file using the --initial flag.

Example :

proxysql --initial -f -c /etc/proxysql.cnf

There are a few things you should know before using this flag : Initial flag

Why do entries in mysql_servers duplicated?

A few user have raised the question of why the writer host gets duplicated into the reader hostgroup.

Okay, so this behaviour is intensional!
And it is controlled by mysql-monitor_writer_is_also_reader in Monitor Module

When we load MYSQL SERVERS, our writer host also gets configured in the reader hostgroup automatically by ProxySQL to handle all those queries which are redirected to reader hostgroup in case no slaves are online.
This feature is dependent on reader/writer hostgroup which we configured in table mysql_replication_hostgroups.

Note : LOAD MYSQL SERVERS TO RUNTIME processes both mysql_servers and mysql_replication_hostgroups tables.

How can I kill a connection ?

You can find the processlist information in the ProxySQL Admin stats table by executing select * from stats_mysql_processlist;. This table contains the following fields

  ThreadID: Thread Identifier
 SessionID: Session Identifier
      user: Authentication User
        db: Connected Database
  cli_host: Client host / IP
  cli_port: Client port
 hostgroup: Hostgroup Identifier
l_srv_host: Listening host / IP (ProxySQL)
l_srv_port: Listening port (ProxySQL
  srv_host: MySQL host / IP (Backend MySQL instance)
  srv_port: MySQL port (Backend MySQL instance)
   command: Command State
   time_ms: Execution time
      info: SQL Statement executing

From here you can identify the SessionID and KILL CONNECTION e.g.:

ProxySQL Admin> KILL CONNECTION 1; 

When does query routing get disabled?

When we enable transaction_persistent for a specific user and application to execute transactions, it will always use the same host to execute all queries to get more accurate results.
Please note that it disables query routing.

Admin> SELECT username, default_hostgroup, transaction_persistent, fast_forward FROM mysql_users;
+----------+-------------------+------------------------+--------------+
| username | default_hostgroup | transaction_persistent | fast_forward |
+----------+-------------------+------------------------+--------------+
| root     | 0                 | 1                      | 0            |
+----------+-------------------+------------------------+--------------+

More Detail : Example

Note – By default sysbench uses transactions and prepared statements.
To disable transactions and ps make use of --oltp-test-mode=nontrx and --db-ps-mode=disable respectively.

How can I drain connections from a ProxySQL instance?

Stop the listeners so no new connections are accepted using the “pause” feature. Existing connections are maintained and running transactions are allowed to complete so that applications can disconnect gracefully:

ProxySQL Admin> PROXYSQL PAUSE;

To start listening for new connections again it is possible to resume with:

ProxySQL Admin> PROXYSQL RESUME;

Reference: ISSUE-337

Feature X doesn’t work. Please advise

Please read How To ask Questions The Smart Way, then ask on the forum or report a bug

Disclaimer: Thyrsus Enterprises is not a help desk .

How do I configure ProxySQL to connect to MySQL?

Port 6032 is the default port used by the “Admin interface”. Through this interface you can configure ProxySQL and get metrics from it by using a normal MySQL client.

For configuration, also check out the documentation.

How can I connect to a MySQL server through ProxySQL?

In order to connect to MySQL servers through ProxySQL you should connect to Port 6033 (by default).

For configuration, also check out the documentation.

Does ProxySQL support ip address whitelist?

ProxySQL supports some sort of IP address whitelisting. Field mysql_query_rules.client_addr can be used to filter traffic based on clients addresses, therefore it is possible to allow traffic from specific addresses while blocking everything else.
The catch here is that the filtering is done on the queries only: clients not in the “whitelist” can still be able to connect to ProxySQL, although their queries will be blocked.

Also check out the documentation.

Are requests load balanced for a single connection?

Yes, by default, it is possible that the requests coming from a single connection are evenly distributed among all the backends of the same hostgroup.

Also check out the documentation.

Why do I get Detected a broken connection during query on .... : 2006, MySQL server has gone away

This message means that the backend server had closed the connection, but ProxySQL reports the generic error message because it has no knowledge of the root reason. As for now we have seen that the most frequent reasons for this error to appear are: * wait_timeout * large packet

In ProxySQL Cluster, why does the synchronization of mysql_users generate two records?

When you add a user in mysql_users with both backend=1 and frontend=1, you are actually creating 2 users: one for frontend and one for backend. Although in mysql_users they can be represented (only represented) as one row, they are actually 2 users. In fact, runtime_mysql_users shows 2 users and 2 rows.

ProxySQL uses runtime_mysql_users for syncing users, thus 2 users are synchronized, and in the receiving nodes they are recorded as 2 rows in mysql_users too.
Once again: even if you see only 1 row, they are actually 2 users.