ProxySQL in its versions up to 1.x did not natively support Percona XtraDB Cluster (PXC). Instead, it relied on the flexibility offered by the scheduler. This approach allowed users to implement their own preferred way to manage the ProxySQL behaviour in relation to the Galera events.
From version 2.0 we can use native ProxySQL support for PXC.. The mechanism to activate native support is very similar to the one already in place for group replication.
In brief it is based on the table [runtime_]mysql_galera_hostgroups and the information needed is mostly the same:
- writer_hostgroup: the hostgroup ID that refers to the WRITER
- backup_writer_hostgroup: the hostgoup ID referring to the Hostgorup that will contain the candidate servers
- reader_hostgroup: The reader Hostgroup ID, containing the list of servers that need to be taken in consideration
- offline_hostgroup: The Hostgroup ID that will eventually contain the writer that will be put OFFLINE
- active: True[1]/False[0] if this configuration needs to be used or not
- max_writers: This will contain the MAX number of writers you want to have at the same time. In a sane setup this should be always 1, but if you want to have multiple writers, you can define it up to the number of nodes.
- writer_is_also_reader: If true [1] the Writer will NOT be removed from the reader HG
- max_transactions_behind: The number of wsrep_local_recv_queue after which the node will be set OFFLINE. This must be carefully set, observing the node behaviour.
- comment: I suggest to put some meaningful notes to identify what is what.
Given the above let us see what we need to do in order to have a working galera native solution.
I will have three Servers:
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192.168.1.205 (Node1) 192.168.1.21 (Node2) 192.168.1.231 (node3) |
As set of Hostgroup, I will have:
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Writer HG-> 100 Reader HG-> 101 BackupW HG-> 102 offHG HG-> 9101 |
To set it up
Servers first:
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INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.205',101,3306,1000); INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.21',101,3306,1000); INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.231',101,3306,1000); |
Then the galera settings:
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insert into mysql_galera_hostgroups (writer_hostgroup,backup_writer_hostgroup,reader_hostgroup, offline_hostgroup,active,max_writers,writer_is_also_reader,max_transactions_behind) values (100,102,101,9101,0,1,1,16); |
As usual if we want to have R/W split we need to define the rules for it:
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insert into mysql_query_rules (rule_id,proxy_port,schemaname,username,destination_hostgroup,active,retries,match_digest,apply) values(1040,6033,'windmills','app_test',100,1,3,'^SELECT.*FOR UPDATE',1); insert into mysql_query_rules (rule_id,proxy_port,schemaname,username,destination_hostgroup,active,retries,match_digest,apply) values(1041,6033,'windmills','app_test',101,1,3,'^SELECT.*@@',1); save mysql query rules to disk; load mysql query rules to run; |
Then another important variable… the server version, please do yourself a good service ad NEVER use the default.
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update global_variables set variable_value='5.7.0' where variable_name='mysql-server_version'; LOAD MYSQL VARIABLES TO RUNTIME;SAVE MYSQL VARIABLES TO DISK; |
Finally activate the whole thing:
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save mysql servers to disk; load mysql servers to runtime; |
One thing to note before we go ahead. In the list of servers I had:
- Filled only the READER HG
- Used the same weight
This because of the election mechanism ProxySQL will use to identify the writer, and the (many) problems that may be attached to it.
For now let us go ahead and see what happens when I load this information to runtime.
Before running the above commands:
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+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ | weight | hostgroup | srv_host | srv_port | status | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us | +--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ +--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ |
After:
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+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ | weight | hostgroup | srv_host | srv_port | status | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us | +--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ | 1000 | 100 | 192.168.1.231 | 3306 | ONLINE | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 501 | | 1000 | 101 | 192.168.1.231 | 3306 | ONLINE | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 501 | | 1000 | 101 | 192.168.1.21 | 3306 | ONLINE | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 546 | | 1000 | 101 | 192.168.1.205 | 3306 | ONLINE | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 467 | | 1000 | 102 | 192.168.1.21 | 3306 | ONLINE | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 546 | | 1000 | 102 | 192.168.1.205 | 3306 | ONLINE | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 467 | +--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ mysql> select * from runtime_mysql_galera_hostgroups \G *************************** 1. row *************************** writer_hostgroup: 100 backup_writer_hostgroup: 102 reader_hostgroup: 101 offline_hostgroup: 9101 active: 0 <----------- note this max_writers: 1 writer_is_also_reader: 1 max_transactions_behind: 16 comment: NULL 1 row in set (0.01 sec) |
As we can see, ProxySQL had taken the nodes from my READER group and distribute them adding node 1 in the writer and node 2 as backup_writer.
But – there is a but – wasn’t my rule set with Active=0? Indeed it was, and I assume this is a bug (#Issue 1902).
The other thing we should note is that ProxySQL had elected as writer node 3 (192.168.1.231).
As I said before what should we do IF we want to have a specific node as preferred writer?
We need to modify its weight. So say we want to have node 1 (192.168.1.205) as writer we will need something like this:
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INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.205',101,3306,10000); INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.21',101,3306,100); INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.231',101,3306,100); |
Doing that will give us :
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+--------+-----------+---------------+----------+--------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+ | weight | hostgroup | |