Saturday, November 2, 2019

Manage InnoDB Cluster using MySQL Shell Extensions

At times, when playing with different InnoDB Clusters for testing (I usually deploy all Group Replication instances on the same host on different ports) I find myself stopping the group and doing operations on every instance (e.g. a static reconfiguration). Or I may need to shutdown all instances at once. Scripting is the usual approach, but in addition, MySQL Shell offers a very nice (and powerful) way to integrate custom scripts into the Shell itself to manage an InnoDB Cluster. This is the purpose of MySQL Shell extensions, to create new custom reports and functions and have the flexibility to manage one or more instances at once. I found particularly practical the new plugin feature, introduced in MySQL Shell 8.0.17, that can aggregate reports and functions under the same umbrella: the plugin.

As an example of the things that are possible, I have modified Rene's great example so to stop Group Replication in a shot from MySQL Shell, and it's particularly easy, check the following script.

  1. Create directory  ~/.mysqlsh/plugins/ext/idc/
  2. Create there init.js script as follows, it will be loaded at MySQL Shell startup.

// Get cluster object, only if session is created
function get_cluster(session, context) {
  if (session) {
    try {
      return dba.getCluster();
    } catch (err) {
      throw "A session to a cluster instance is required: " + err.message
  } else {
    throw "A session must be established to execute this " + context

function stop_cluster() {
  var cluster = get_cluster(shell.getSession(), "function");
  var data = cluster.status();
  var topology = data.defaultReplicaSet.topology;
  var sess = shell.getSession()
  var uri = sess.getUri()
  var user = (uri.split('//')[1]).split('@')[0]

  // iterate through members in the cluster
  for (index in topology) {
if (topology[index].status=="ONLINE")
print("\n-----> " + topology[index].address + " is ONLINE and will be evicted from GR\n")

var sess = shell.connect(user + "@" + topology[index].address)
var result = sess.runSql("STOP GROUP_REPLICATION;")

//print(JSON.stringify(result, null, 4))

  // Reconnect original session

// Creates the extension object
var idc = shell.createExtensionObject()

// Adds the desired functionality into it
shell.addExtensionObjectMember(idc, "stopCluster", stop_cluster, {
  brief: "Stops GR on all nodes, secondaries first, primary instance the last.",
  details: [
    "This function will stop GR on all nodes.",
    "The information is retrieved from the cluster topology."]});

// Register the extension object as a global object
shell.registerGlobal("idc", idc, {
  brief:"Utility functions for InnoDB Cluster."})

The script defines stop_cluster function that is invoked with idc.stopCluster() and:

  1. Get the cluster object from the session (session against any member must be created beforehand)
  2. Fetch topology from cluster object
  3. Iterate through members belonging to the topology and get the address
  4. For every member, establish a session using same session user (e.g. root or whatever, it is a prerequisite to administer a cluster with the same user)
  5. Send command to stop Group Replication
  6. After iterating through all members, reset the original session
The script also creates an extension object, registers it as global object and adds the function so it can be invoked as follows:

It is also possible to restart the cluster with the built-in dba global object, with function dba.rebootClusterFromCompleteOutage(); 

So in short, it is possible to start and stop the cluster with one command and from the same MySQL Shell session. This is only a quick skeleton (can be improved e.g. like stopping GR starting by secondary instances, and the primary at last) to connect to instances and do operations, there is no limit to the number of things that are possible. Read more on LeFred's blog here

Saturday, September 21, 2019

MySQL Server Performance Tuning: The Perfect Scalability

When data and concurrency grow, together with queries complexity, a standard configuration does not fit anymore. This content walks through the ways MySQL has to adapt to an ever-increasing amount of data in context of tuning, under the heading “multiplication”:
—Scaling up through partitioning and how partitioning can help manage/archive data
—How to relocate binlog, undo, redo, tablespaces, or disk temporary tables and more on different mount points to take advantage of multiple storages and tackle I/O bottlenecks
—All improvements to parallel slave replication
—A quick OS approach, to verify swapping and affinity tuning take the most out of the machine.

All of this with different approaches to monitor the instance to spot what parts of the system and what queries need to be considered, mainly using:

Sys Schema
Global Status

I presented this content at last Oracle Open World 2019 as a Hands-On Lab.

Friday, September 20, 2019

How To Bulk Import Data Into InnoDB Cluster?

If you need to do bulk importing into InnoDB Cluster, it is certainly possible to do so by using any of:

Unfortunately both imports will add load to instances and to channels interconnecting instances: data imported on the primary instance needs to be replicated to the rest of instances. And the bigger the data to import, the higher the load (and this could end up affecting performance). The import operation could be batched to reduce load, and Group Replication allows at least to throttle workload with flow control or to split messages in several smaller messages with group_replication_communication_max_message_size option.

How to import data into InnoDB Cluster?
But in case data to import is a whole table (MySQL 8 adds also flexibility to swap partitions and tables, may become handy), or data can be first loaded into an InnoDB table, there's simple way to have an arbitrary amount of data pushed to InnoDB Cluster, and it takes advantage of tablespaces copying feature. I made a quick test to import a table.

I created the table t5 on an arbitrary instance and added a few rows. Then exported as in the instructions (does nothing but flush it and create an auxiliary .cnf file for definition validation at import time, not mandatory to use it but recommended):


On the InnoDB Cluster setup, I created the table t5 with same definition from the primary, then again on the primary:


This will remove the t5.ibd tablespace on all the 3 instances. And with a simple SELECT, I made sure that this is as expected:

mysql> select * from test.t5;
ERROR 1814 (HY000): Tablespace has been discarded for table 't5'

After that, I copied t5.ibd from the former instance under the related schema folder in *each* GR node.
Let's check initial GTID set:

mysql> select @@GLOBAL.GTID_EXECUTED;
| @@GLOBAL.GTID_EXECUTED                                     |
| 550fa9ee-a1f8-4b6d-9bfe-c03c12cd1c72:1-270:1000011-1000014 |
1 row in set (0.00 sec)

Then on the primary, did:

Query OK, 0 rows affected, 1 warning (0.03 sec)

I am lazy and did not perform validation using .cfg (more from the instructions):

mysql> show warnings;
| Level   | Code | Message                                                                                                                                 |
| Warning | 1810 | InnoDB: IO Read error: (2, No such file or directory) Error opening './test/t5.cfg', will attempt to import without schema verification |
1 row in set (0.00 sec)

And all the tablespaces are loaded from local file system into the GR member. And new GTID set is:

mysql> select @@GLOBAL.GTID_EXECUTED;
| @@GLOBAL.GTID_EXECUTED                                     |
| 550fa9ee-a1f8-4b6d-9bfe-c03c12cd1c72:1-271:1000011-1000014 |
1 row in set (0.00 sec)

Let's test it's all ok:

mysql> select * from test.t5;
| a    |
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
|    6 |
|    7 |
|  777 |
8 rows in set (0.00 sec)

So data will be available on the rest of the nodes at no bandwidth and protocol cost, only this is indeed replicated, from binlog.

# at 2714
#190919  1:34:34 server id 1  end_log_pos 2821  Query   thread_id=34    exec_time=0     error_code=0
SET TIMESTAMP=1568849674/*!*/;
SET @@SESSION.GTID_NEXT= 'AUTOMATIC' /* added by mysqlbinlog */ /*!*/;
# End of log file

Most important, I broke nothing!

mysql> SELECT MEMBER_ID, MEMBER_STATE FROM performance_schema.replication_group_members;
| 43a67ea3-e1a0-11e7-8a9a-0021f66e910e | ONLINE |
| 45ab082d-e1a0-11e7-8b73-0021f66e910e | ONLINE |
| 48be28c0-e1a0-11e7-8c19-0021f66e910e | ONLINE |
3 rows in set (0.00 sec)

To wrap up, instead of loading GB or TB into InnoDB Cluster and have the cluster replicate massive amount of rows, this trick can push your data at no cost.
Comments are welcome!