Feb
20
2019
--

ProxySQL Native Support for Percona XtraDB Cluster (PXC)

galera proxy content image

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:

192.168.1.205 (Node1)
  192.168.1.21  (Node2)
  192.168.1.231 (node3)

As set of Hostgroup, I will have:

Writer  HG-> 100
Reader  HG-> 101
BackupW HG-> 102
offHG   HG-> 9101

To set it up

Servers first:

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:

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:

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.

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:

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:

  1. Filled only the READER HG
  2. 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:

+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 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:

+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 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:

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 :

+--------+-----------+---------------+----------+--------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| weight | hostgroup | srv_host      | srv_port | status | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us |
+--------+-----------+---------------+----------+--------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 10000  | 100       | 192.168.1.205 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 2209       |
| 100    | 101       | 192.168.1.231 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 546        |
| 100    | 101       | 192.168.1.21  | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 508        |
| 10000  | 101       | 192.168.1.205 | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 2209       |
| 100    | 102       | 192.168.1.231 | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 546        |
| 100    | 102       | 192.168.1.21  | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 508        |
+--------+-----------+---------------+----------+--------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+

If you noticed, given we had set the WEIGHT in node 1 higher, this node will become also the most utilized for reads.
We probably do not want that, so let us modify the reader weight.

update mysql_servers set weight=10 where hostgroup_id=101 and hostname='192.168.1.205';

At this point if we trigger the failover, with set global wsrep_reject_queries=all; on node 1.
ProxySQL will take action and will elect another node as writer:

+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| weight | hostgroup | srv_host      | srv_port | status  | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 100    | 100       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 562        |
| 100    | 101       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 562        |
| 100    | 101       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0	      | 0           | 0	      | 0                 | 0               | 0               | 588        |
| 100    | 102       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 588        |
| 10000  | 9101      | 192.168.1.205 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 468        |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+

Node 3 (192.168.1.231) is the new writer and node 1 is in the special group for OFFLINE.
Let see now what will happen IF we put back node 1.

+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| weight | hostgroup | srv_host      | srv_port | status  | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 10000  | 100       | 192.168.1.205 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 449        |
| 100    | 101       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 532        |
| 100    | 101       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 569        |
| 10000  | 101       | 192.168.1.205 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 449        |
| 100    | 102       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 532        |
| 100    | 102       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 569        |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+

Ooops the READER has come back with the HIGHEST value and as such it will be the most used node, once more. To fix it, we need to re-run the update as before.

But there is a way to avoid this? In short the answer is NO!
This, in my opinion, is BAD and is worth a feature request, because this can really put a node on the knees.

Now this is not the only problem. There is another point that is probably worth discussion, which is the fact ProxySQL is currently doing FAILOVER/FAILBACK.

Failover, is obviously something we want to have, but failback is another discussion. The point is, once the failover is complete and the cluster has redistributed the incoming requests, doing a failback is an impacting operation that can be a disruptive one too.

If all nodes are treated as equal, there is no real way to prevent it, while if YOU set a node to be the main writer, something can be done, let us see what and how.
Say we have:

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',101,3306,100);
INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.231',101,3306,100);
+--------+-----------+---------------+----------+--------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 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       | 192.168.1.205 | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 470        |
| 100    | 101       | 192.168.1.231 | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 558        |
| 100    | 101       | 192.168.1.21  | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 613        |
| 10     | 101       | 192.168.1.205 | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 470        |
| 100    | 102       | 192.168.1.231 | 3306     | ONLINE | 0        | 0        | 0      | 0	  | 0           | 0	  | 0                 | 0               | 0               | 558        |
| 100    | 102       | 192.168.1.21  | 3306     | ONLINE | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 613        |
+--------+-----------+---------------+----------+--------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+

Let us put the node down
set global wsrep_reject_queries=all;

And check:

+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| weight | hostgroup | srv_host      | srv_port | status  | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 100    | 100       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0	      | 0           | 0	      | 0                 | 0               | 0               | 519        |
| 100    | 101       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0	      | 0           | 0	      | 0                 | 0               | 0               | 519        |
| 100    | 101       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0	      | 0           | 0	      | 0                 | 0               | 0               | 506        |
| 100    | 102       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 506        |
| 1000   | 9101      | 192.168.1.205 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 527        |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+

We can now manipulate the weight in the special OFFLINE group and see what happen:

update mysql_servers set weight=10 where hostgroup_id=9101 and hostname='192.168.1.205'

Then I put the node up again:
set global wsrep_reject_queries=none;

+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| weight | hostgroup | srv_host      | srv_port | status  | ConnUsed | ConnFree | ConnOK | ConnERR | MaxConnUsed | Queries | Queries_GTID_sync | Bytes_data_sent | Bytes_data_recv | Latency_us |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+
| 100    | 100       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 537        |
| 100    | 101       | 192.168.1.231 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 537        |
| 100    | 101       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 573        |
| 10     | 101       | 192.168.1.205 | 3306     | ONLINE  | 0        | 0        | 0      | 0	   | 0           | 0	   | 0                 | 0               | 0               | 458	|
| 100    | 102       | 192.168.1.21  | 3306     | ONLINE  | 0        | 0        | 0      | 0	   | 0           | 0	   | 0                 | 0               | 0               | 573	|
| 10     | 102       | 192.168.1.205 | 3306     | ONLINE  | 0        | 0        | 0      | 0       | 0           | 0       | 0                 | 0               | 0               | 458        |
+--------+-----------+---------------+----------+---------+----------+----------+--------+---------+-------------+---------+-------------------+-----------------+-----------------+------------+

That’s it, the node is back but with no service interruption.

At this point we can decide if make this node reader like the others, or wait and plan a proper time of the day when we can put it back as writer, while, in the meanwhile it has a bit of load to warm its bufferpool.

The other point – and important information – is what is ProxySQL is currently checking on Galera? From reading the code Proxy will trap the following:

  • read_only
  • wsrep_local_recv_queue
  • wsrep_desync
  • wsrep_reject_queries
  • wsrep_sst_donor_rejects_queries
  • primary_partition

Plus the standard sanity checks on the node.

Finally to monitor the whole situation we can use this:

mysql> select * from mysql_server_galera_log order by time_start_us desc limit 10;
+---------------+------+------------------+-----------------+-------------------+-----------+------------------------+-------------------+--------------+----------------------+---------------------------------+-------+
| hostname      | port | time_start_us    | success_time_us | primary_partition | read_only | wsrep_local_recv_queue | wsrep_local_state | wsrep_desync | wsrep_reject_queries | wsrep_sst_donor_rejects_queries | error |
+---------------+------+------------------+-----------------+-------------------+-----------+------------------------+-------------------+--------------+----------------------+---------------------------------+-------+
| 192.168.1.231 | 3306 | 1549982591661779 | 2884            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.21  | 3306 | 1549982591659644 | 2778            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.205 | 3306 | 1549982591658728 | 2794            | YES               | NO        | 0                      | 4                 | NO           | YES                  | NO                              | NULL  |
| 192.168.1.231 | 3306 | 1549982586669233 | 2827            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.21  | 3306 | 1549982586663458 | 5100            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.205 | 3306 | 1549982586658973 | 4132            | YES               | NO        | 0                      | 4                 | NO           | YES                  | NO                              | NULL  |
| 192.168.1.231 | 3306 | 1549982581665317 | 3084            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.21  | 3306 | 1549982581661261 | 3129            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.205 | 3306 | 1549982581658242 | 2786            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
| 192.168.1.231 | 3306 | 1549982576661349 | 2982            | YES               | NO        | 0                      | 4                 | NO           | NO                   | NO                              | NULL  |
+---------------+------+------------------+-----------------+-------------------+-----------+------------------------+-------------------+--------------+----------------------+---------------------------------+-------+

As you can see above the log table keeps track of what is changed. In this case, it reports that node 1 has wsrep_reject_queries activated, and it will continue to log this until we set wsrep_reject_queries=none.

Conclusions

ProxySQL galera native integration is a useful feature to manage any Galera implementation, no matter whether it’s Percona PXC, MariaDB cluster or MySQL/Galera.

The generic approach is obviously a good thing, still it may miss some specific extension like we have in PXC with the performance_schema pxc_cluster_view table.

I’ve already objected about the failover/failback, and I am here again to remind you: whenever you do a controlled failover REMEMBER to change the weight to prevent an immediate failback.

This is obviously not possible in the case of a real failover, and, for instance, a simple temporary eviction will cause two downtimes instead only one. Some environments are fine with that others not so.

Personally I think there should be a FLAG in the configuration, such that we can decide if failback should be executed or not.

 

Mar
20
2018
--

Webinar Thursday, March 22, 2018: Percona XtraDB Cluster 5.7 with ProxySQL for Your MySQL High Availability and Clustering Needs

MySQL high availability

MySQL high availabilityPlease join Percona’s Ramesh Sivaraman (QA Engineer) and Krunal Bauskar (Software Engineer, Percona XtraDB Cluster Lead) as they present Percona XtraDB Cluster 5.7 with ProxySQL for Your MySQL High Availability and Clustering Needs on Thursday, March 22, 2018 at 8:30 am PDT (UTC-7) / 11:30 am EDT (UTC-4).

Percona has developed Percona XtraDB Cluster (based on Galera Cluster) and integrated it with ProxySQL to address MySQL high availability and clustering. These two products working together provide a great out-of-the-box synchronous replication setup.

In this webinar, we’ll look at why this is a great solution, and what types of deployments you should consider using it in.

Register for the webinar now.

MySQL High AvailabilityKrunal is Percona XtraDB Cluster lead at Percona. He is responsible for day-to-day Percona XtraDB Cluster development, what goes into Percona XtraDB Cluster, bug fixes, releases, etc. Before joining Percona, he worked as part of InnoDB team at MySQL/Oracle. He authored most of the temporary table revamp work, undo log truncate, atomic truncate and a lot of other features. In the past, he was associated with Yahoo! Labs researching big data problems, and a database startup that is now part of Teradata. His interests mainly include data-management at any scale and he has been practicing it for more than decade.

MySQL High AvailabilityRamesh joined the Percona QA Team in March 2014. Prior to joining Percona, he provided MySQL database support to various service- and product-based Internet companies. Ramesh’s professional interests include writing shell/Perl scripts to automate routine tasks, and new technology. Ramesh lives in Kerala, the southern part of India, close to his family.

The post Webinar Thursday, March 22, 2018: Percona XtraDB Cluster 5.7 with ProxySQL for Your MySQL High Availability and Clustering Needs appeared first on Percona Database Performance Blog.

Dec
19
2017
--

Webinar Q&A: Percona XtraDB Cluster 101

Percona XtraDB Cluster

Percona XtraDB ClusterIn this blog, we will answer questions from our webinar on Percona XtraDB Cluster 101.

Recently (7 Dec 2017) I presented a webinar about Percona XtraDB Cluster 101. Firstly, thanks to all the attendees: we had a great webinar with quite some interesting questions and feedback.

Through this blog, I’ll answer most of the questions that were raised during the webinar.

Q. How does the need for the acknowledgment from other nodes affect the speed of writes?

A. There are two parts to replication: delivering a transaction (including acknowledgment) and applying the transaction. Generally, the first part is pretty quick and dictated by the network latency. The second part is time-consuming, but happens asynchronously. So acknowledging a transaction from other nodes is not that time-consuming.

Q. How can geo-distributed nodes affect the speed of writes?

A. The longest node dictates cluster performance (in terms of latency). You can’t write faster than the time it takes for a packet to reach the longest node (round-trip-latency). So geo-distribution does affect write performance.

Q. Would you consider Master -> Slave replication in RDS a traditional replication of MySQL? And how easy is it replicating from PXC to RDS if its possible

A. If an application doesn’t need high availability, then a user can explore the MASTER-SLAVE replication. But I would argue that if I am going to spend time booting two servers (MASTER and SLAVE), then why not boot both as MASTER (through Percona XtraDB Cluster). This ensures HA and write-scalability. Percona XtraDB Cluster is flexible for all topologies, and can act as async-master or async-slave too.

Q. Moving forward, is there a plan to deal with version control tools like Flyway that still uses Get locks?

A. Statements like GET_LOCK that establish local locks at the said node are not cluster-safe, so they are blocked with

pxc_strict_mode=ENFORCING

 and not recommended for use. With that said, if the application/user tries to use these statements in a non-conflicting way (with the load directed to single master) it could still work.

Q. With an ASYNC slave, can you use GTID? I know there is a bug(s) that prevent this currently from working 100% in MariaDB (though the bug is close to being fixed – MDEV-10715)?

A. Yes, you can use GTID with async-slave. MariaDB has different implementation of GTID so I am not in a position to comment on the latter part.

Q. Do tables need to have a primary key for the cluster to work?

A. Yes, all tables that you plan to use in a cluster should have a primary key (

pxc_strict_mode=ENFORCING

 enforces this criterion). This is mainly needed for conflict resolution, when the same conflicting workload is executed on multiple-nodes.

Q. What is the best wsrep_sst_method? (for huge database)

A. Percona XtraDB Cluster recommends using XtraBackup. It doesn’t lock the tables for the complete SST life-time, so you can continue to use the node while it is acting as DONOR.

Q. Is the “show processlist” node-specific? Is there an equivalent command to show the whole cluster process list?

A. Yes, show processlist is node specific. There is currently no way to cluster-wide-processlist.

Q. does PXC support partitioned tables?

A. Yes, using InnoDB native partitioning.

Q. These nodes (PXC-nodes) are api nodes or data nodes ?

A. Data nodes.

Q. If cluster went down then everytime it follow SST/IST?

A. It depends. If there is DONOR that has a missing write-set, then the node can rejoin through IST else SST.

Q. Around how much time it will take to join the cluster?

A. The time a node takes to join back depends on the size of the data. Generally, the time for SST is longer than IST. The good part is with 5.7.17+ we have considerably reduced the time for IST, so that a node can join faster than before.

Q. How does IST (incremental state transfer) process affect cluster performance?

A. IST is asynchronous and doesn’t emit FLOW_CONTROL, so cluster can continue to perform as normal. A small slice of DONOR bandwidth is used to send data to the JOINER, but it is not that significant to affect the overall cluster performance.

Q. How do you handle a situation when three simultaneous transactions try to insert auto_increment value?

A. Percona XtraDB Cluster has a concept of wsrep_auto_increment_control that adjust the increment size on each node based on a number of nodes in the cluster. Please check this link for more details.

Q. Imagine that a table A has a trigger on insert that inserts data into another table B. And there are two concurrent transactions: TA inserts into table A (and the trigger makes an insert into B) and TB that inserts the same data directly into B. Will such a conflict – insert from TB and from trigger – be detected?

A. Yes. A transaction can touch multiple data-objects and when the conflict resolution is done, it will check all the objects that transaction is planning to modify before certifying a transaction is safe to apply.

Q. How PXC will make sure of data integrity with parallel processing?

A. Percona XtraDB Cluster has conflict resolution protocol. This protocol is based on FIRST COMMITTER WIN principle that ensures only the first transaction (from a group of a conflicting transaction) commits to cluster.

Q. I’ve created a three node cluster and replication is working. I’d like to copy our production data to the cluster since exporting and importing from MySQL takes a long time. Should I have waited to bootstrap the cluster until the data directory is transferred?

A. If you already have a cluster in place then you are simply adding new tables to the cluster. You can start adding (LOADING) the tables and these tables are immediately replicated to the other nodes of the cluster. An alternative would be to start the first node of the cluster with the pre-loaded data that then becomes cluster state. Other joining nodes copy it over through SST.

Q. Do we have an option to autospinup the compute nodes in a cloud? If PXC will have that option or do we manually need to spinup the Instance and setup the replication?

A. You will have to manually configure it.

Q. Why does XtraBackup not work due bootstrapping but works perfectly after bootstrapping? rsync is working in both cases.

A. Not sure I get the question completely, but XtraBackup works in all scenarios. If you are facing any issue, please log it on launchpad.

Q. As per flow control, one node waits for the other node to be in sync. Won’t there be latency in writing the data?

A. The transaction originated from one node needs to get replicated on other nodes of the cluster. This is what we can call latency and is dictated by network latency. Flow-control is mainly to regulate a scenario wherein one node of the cluster falls way behind other nodes of the cluster.

Q. Can we set up PXC using AWS EC2?

A. Yes.

Once again, thanks for taking time to attend the webinar. If you have more questions, then please post them to the Percona XtraDB Cluster forum here. Also, we have a lot of blogs about Percona XtraDB Cluster. Make sure you check them out here.

Nov
02
2017
--

MySQL vs. MariaDB: Reality Check

MySQL vs. MariaDB

MySQL vs. MariaDBIn this blog, we’ll provide a comparison between MySQL vs. MariaDB (including Percona Server for MySQL).

Introduction

The goal of this blog post is to evaluate, at a higher level, MySQL, MariaDB and Percona Server for MySQL side-by-side to better inform the decision making process. It is largely an unofficial response to published comments from the MariaDB Corporation.

It is worth noting that Percona Server for MySQL is a drop-in compatible branch of MySQL, where Percona contributes as much as possible upstream. MariaDB Server, on the other hand, is a fork of MySQL 5.5. They cherry-picked MySQL features, and don’t guarantee drop-in compatibility any longer.

MySQL Percona Server for MySQL* MariaDB Server
Protocols MySQL protocol over port 3306, X Protocol over port 33060 MySQL protocol over port 3306, X Protocol over port 33060 MySQL protocol, MariaDB Server extensions
Community –
Source Code
Open Source Open Source Open Source
Community – Development Open Source, contributions via signing the Oracle Contributor Agreement (OCA) Open Source Open Source, contributions via the new BSD license or signing the MariaDB Contributor Agreement (MCA)
Community – Collaboration Mailing list, forums, bugs system Mailing list, forums, bugs system (Jira, Launchpad) Mailing list, bugs system (Jira), IRC channel
Core –
Replication
MySQL replication with GTID MySQL replication with GTID MariaDB Server replication, with own GTID, compatible only if MariaDB Server is a slave to MySQL, not vice versa
Core –
Routing
MySQL Router (GPLv2) ProxySQL (GPLv3) MariaDB MaxScale (Business Source License)
Core –
Partitioning
Standard Standard Standard, with extra engines like SPIDER/CONNECT that offer varying levels of support
Tool –
Editing
MySQL Workbench for Microsoft Windows, macOS, and Linux MySQL Workbench for Microsoft Windows, macOS, and Linux Webyog’s SQLYog for Microsoft Windows (MySQL Workbench notes an incompatible server)
Tool –
Monitoring
MySQL Enterprise Monitor Percona Monitoring & Management (PMM) (100% open source) Webyog’s Monyog
Scalability –
Client Connections
MySQL Enterprise Threadpool Open Source Threadpool with support for priority tickets Open Source Threadpool
Scalability –
Clustering
MySQL Group Replication MySQL Group Replication, Percona XtraDB Cluster (based on a further engineered Galera Cluster) MariaDB Enterprise Cluster (based on Galera Cluster)
Security –
Encryption
Tablespace data-at-rest encryption. Amazon KMS, Oracle Vault Enterprise Edition Tablespace data-at-rest encryption with Keyring Vault plugin Tablespace and table data-at-rest encryption. Amazon KMS, binlog/redo/tmp file with Aria tablespace encryption
Security –
Data Masking
ProxySQL data masking ProxySQL data masking MariaDB MaxScale data masking
Security –
Firewall
MySQL Enterprise Firewall ProxySQL Firewall MariaDB MaxScale Firewall
Security –
Auditing
MySQL Enterprise Audit Plugin Percona Audit Plugin (OSS) MariaDB Audit Plugin (OSS)
Analytics No ClickHouse MariaDB ColumnStore
SQL –
Common Table Expressions
In-development for MySQL 8.0 (now a release candidate) In-development for MySQL 8.0 (now a release candidate) Present in MariaDB Server 10.2
SQL –
Window Functions
In-development for MySQL 8.0 (now a release candidate) In-development for MySQL 8.0 (now a release candidate) Present in MariaDB Server 10.2
Temporal –
Log-based rollback
No No In development for MariaDB Server 10.3
Temporal – system versioned tables No No In development for MariaDB Server 10.3
JSON JSON Data type, 21 functions JSON Data type, 21 functions No JSON Data Type, 26 functions
Official
client connectors
C (libmysqlclient), Java, ODBC, .NET, Node.js, Python, C++, mysqlnd for PHP C (libmysqlclient), Java, ODBC, .NET, Node.js, Python, C++, mysqlnd for PHP C (libmariadbclient), Java, ODBC
Usability – CJK Language support Gb18030, ngram & MeCab for InnoDB full-text search Gb18030, ngram & MeCab for InnoDB full-text search No
Monitoring – PERFORMANCE
_SCHEMA
Thorough instrumentation in 5.7, sys schema included Thorough instrumentation in 5.7, sys schema included Instrumentation from MySQL 5.6, sys schema not included
Security – Password authentication sha256_password (with caching_sha2_password in 8.0) sha256_password (with caching_sha2_password in 8.0) ed25519 (incompatible with sha256_password)
Security –
Secure out of the box
validate_password on by default, to choose a strong password at the start validate_password on by default, to choose a strong password at the start No
Usability – Syntax differences EXPLAIN FOR CONNECTION <thread_id> EXPLAIN FOR CONNECTION <thread_id> SHOW EXPLAIN FOR <thread_id>
Optimiser –
Optimiser Tracing
Yes Yes No
Optimiser –
Optimiser Hints
Yes Yes No
DBA –
Super readonly mode
Yes Yes No
Security – Password expiry Yes Yes No
Security – Password last changed? Password lifetime? Yes Yes No
Security – VALIDATE_PASSWORD
_STRENGTH()
Yes Yes No
Security – ACCOUNT LOCK/UNLOCK Yes Yes No
Usability – Query Rewriting Yes Yes No
GIS – GeoJSON &
GeoHash functionality
Yes Yes Incomplete
Security – mysql_ssl_rsa_setup Yes Yes No (setup SSL connections manually)
MySQL Utilities Yes Yes No
Backup locks No (in development for 8.0) Yes No
Usability – InnoDB memcached interface Yes Yes No

*Note. Third-party software (such as ProxySQL and ClickHouse) used in conjunction with Percona Server for MySQL is not necessarily covered by Percona Support services.

To get a higher level view of what Percona Server for MySQL offers compared to MySQL, please visit: Percona Server Feature Comparison. Read this for a higher level view of compatibility between MariaDB Server and MySQL written by MariaDB Corporation.

Open Community

MariaDB Server undoubtedly has an open community, with governance mixed between MariaDB Foundation and MariaDB Corporation. There are open developer meetings on average about twice per year, two mailing lists (one for developers and users), an IRC channel and an open JIRA ticket system that logs bugs and feature requests.

Percona Server for MySQL also has an open community. Developer meetings are not open to general contributors, but there is a mailing list, an IRC channel and two systems – Launchpad and JIRA – for logging bugs and feature requests.

MySQL also has an open community where developer meetings are also not open to general contributors. There are many mailing lists, there are a few IRC channels and there is the MySQL bugs system. The worklogs are where the design for future releases happens, and these are opened up when their features are fully developed and  source-code-pushed.

From a source code standpoint, MySQL makes pushes to Github when a release is made; whereas open source development happens for Percona Server for MySQL and MariaDB Server on Github.

Feature development on MySQL continues in leaps and bounds, and Oracle has been an excellent steward of MySQL. Please refer to The Complete List of Features in 5.7, as well as The Unofficial MySQL 8 Optimiser Guide.

Linux distributions have chosen MariaDB Server 5.5, and some have chosen MariaDB Server 10.0/10.1 when there was more backward compatibility to MySQL 5.5/5.6. It is the “default” MySQL in many Linux distributions (such as Red Hat Enterprise Linux, SUSE and Debian). However, Ubuntu still believes that when you ask for MySQL you should get it (and that is what Ubuntu ships).

One of the main reasons Debian switched was due to the way Oracle publishes updates for security issues. They are released as a whole quarterly as Critical Patch Updates, without much detail about individual fixes. This is a policy that is unlikely to change, but has had no adverse effects on distribution.

All projects actively embrace contributions from the open community. MariaDB Server does include contributions like the MyRocks engine developed at Facebook, but so does Percona Server for MySQL. Oracle accepts contributions from a long list of contributors, including Percona. Please see Licensing information for MySQL 5.7 as an example.

A Shared Core Engine

MariaDB Server has differed from MySQL since MySQL 5.5. This is one reason why you don’t get version numbers that follow the MySQL scheme. It is also worth noting that features are cherry-picked at merge time, because the source code has diverged so much since then.

As the table below shows, it took Percona Server for MySQL over four months to get a stable 5.5 release based on MySQL 5.5, while it took MariaDB Server one year and four months to get a stable 5.5 release based on MySQL 5.5. Percona Server for MySQL 5.6 and 5.7 are based on their respective MySQL versions.

MySQL Percona Server for MySQL MariaDB Server
3 December 2010 5.5.8 GA
28 April 2011 5.5.11-20.2 GA
11 April 2012 5.5.23 GA
5 February 2013 5.6.10 GA
7 October 2013 5.6.13-61.0 GA
31 March 2014 10.0.10 GA
17 October 2015 10.1.8 GA
21 October 2015 5.7.9 GA
23 February 2016 5.7.10-3 GA
23 May 2017 10.2.6 GA

 

MySQL is currently at 8.0.3 Release Candidate, while MariaDB Server is at 10.3.2 Alpha as of this writing.

MariaDB Server is by no means a drop-in replacement for MySQL. The risk of moving to MariaDB Server if you aren’t using newer MySQL features may be minimal, but the risk of moving out of MariaDB Server to MySQL is very prevalent. Linux distributions like Debian already warn you of this.

MySQL vs. MariaDB

The differences are beyond just default configuration options. Some features, like time-delayed replication that were present in MySQL since 2013, only make an appearance in MariaDB Server in 2017! (Refer to the MariaDB Server 10.2 Overview for more.) However, it is also worth noting some features such as multi-source replication appeared in MariaDB Server 10.0 first, and only then came to MySQL 5.7.

Extensibility

MySQL and MariaDB Server have a storage engine interface, and this is how you access all engines, including the favored InnoDB/Percona XtraDB. It is worth noting that Percona XtraDB was the default InnoDB replacement in MariaDB Server 5.1, 5.2, 5.3, 5.5, 10.0 and 10.1. But in MariaDB Server 10.2, the InnoDB of choice is upstream MySQL.

Stock MySQL has provided several storage engines beyond just InnoDB (the default) and MyISAM. You can find out more information about 5.7 Supported Engines.

Percona Server for MySQL includes a modified MEMORY storage engine, ships Percona XtraDB as the default InnoDB and also ships TokuDB and MyRocks (currently experimental). MyRocks is based on the RocksDB engine, and both are developed extensively at Facebook.

MariaDB Server includes many storage engines, beyond the default InnoDB. MyISAM is modified with segmented key caches, the default temporary table storage engine is Aria (which is a crash-safe MyISAM), the FederatedX engine is a modified FEDERATED engine, and there are more: CONNECT, Mroonga, OQGRAPH, Sequence, SphinxSE, SPIDER, TokuDB and of course MyRocks.

Storage engines have specific use cases, and have different levels of feature completeness. You should thoroughly evaluate a storage engine before choosing it. We believe that over 90% of installations are fine with just InnoDB or Percona XtraDB. Percona TokuDB is another engine that users who need compression could use. We naturally expect more usage in the MyRocks sphere going forward.

Analytics

MariaDB ColumnStore is the MariaDB solution to analytics and using a column-based store. It is a separate download and product, and not a traditional storage engine (yet). It is based on the now defunct InfiniDB product.

At Percona, we are quite excited by ClickHouse. We also have plenty of content around it. There is no MySQL story around this.

High Availability

High Availability is an exciting topic in the MySQL world, considering the server itself has been around for over 22 years. There are so many solutions out there, and some have had evolution as well.

MySQL provides MySQL Cluster (NDBCLUSTER) (there is no equivalent in the MariaDB world). MySQL also provides group replication (similar to Galera Cluster). Combined with the proxy MySQL Router, and the mysqlsh for administration (part of the X Protocol/X Dev API), you can also get MySQL InnoDB Cluster.

We benefit from the above at Percona, but also put lots of engineering work to make Percona XtraDB Cluster.

MariaDB Server only provides Galera Cluster.

Security

While we don’t want to compare the proprietary MySQL Enterprise Firewall, MariaDB’s recommendation is the proprietary, non-open source MariaDB MaxScale (it uses a Business Source License). We highly recommend the alternative, ProxySQL.

When it comes to encryption, MariaDB Server implements Google patches to provide complete data at rest encryption. This supports InnoDB, XtraDB and Aria temporary tables. The log files can also be encrypted (not present in MySQL, which only allows tablespace encryption and not log file encryption).

When it comes to attack prevention, ProxySQL should offer everything you need.

MySQL Enterprise provides auditing, while MariaDB Server provides an audit plugin as well as an extension to the audit interface for user filtering. Percona Server for MySQL has an audit plugin that sticks to the MySQL API, yet provides user filtering and controls the ability to audit (since auditing is expensive). Streaming to syslog is supported by the audit plugins from Percona and MariaDB.

Supporting Ecosystem and Tools

Upgrading from MySQL to MariaDB Server should be a relatively simple process (as stated above). If you want to upgrade away from MariaDB Server to MySQL, you may face hassles. For tools, see the following table:

Purpose MySQL Percona Server for MySQL MariaDB Server
Monitoring MySQL Enterprise Monitor Percona Monitoring & Management (PMM) (100% open source) Webyog Monyog
Backup MySQL Enterprise Backup Percona XtraBackup MariaDB Backup (fork of Percona XtraBackup)
SQL Management MySQL Workbench MySQL Workbench Webyog SQLyog
Load Balancing & Routing MySQL Router ProxySQL MariaDB MaxScale
Database Firewall MySQL Enterprise Firewall ProxySQL MariaDB MaxScale

 

Enterprise Database Compatibility

MariaDB Server today has window functions and common table expressions (CTEs). These appeared in MariaDB Server 10.2. MySQL 8 is presently in release candidate status and also has similar functionality.

Looking ahead, MariaDB Server 10.3 also includes an Oracle SQL_MODE and a partial PL/SQL parser. This is to aid migration from Oracle to MariaDB Server.

MariaDB Server 10.2 also has “flashback”, developed at Alibaba, to help with log-based rollback using the binary log.

Conclusion

Percona sees healthy competition in the MySQL ecosystem. We support all databases in the ecosystem: MySQL, MariaDB Server and Percona Server for MySQL. Our focus is to provide alternatives to proprietary parts of open source software. Percona has a strong operations focus on compatibility, application scalability, high availability security and observability. We also support many additional tools within the ecosystem, and love integrating and contributing to open source code.

For example, Percona Monitoring and Management (PMM) includes many open source tools like Prometheus, Consul, Grafana, Orchestrator and more. We have made the de facto open source hot backup solution for MySQL, MariaDB Server and Percona Server for MySQL (called Percona XtraBackup). We continue to maintain and extend useful tools for database engineers and administrators in Percona Toolkit. We make Percona XtraDB Cluster safe for deployment out of the box. We have invested in a write-optimized storage engine, TokuDB, and now continue to work with making MyRocks better.

We look forward to supporting your deployments of MySQL or MariaDB Server, whichever option is right for you! If you need assistance on migrations between servers, or further information, don’t hesitate to contact your friendly Percona sales associate.

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