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MySQL 5.7 Multi-threads replication operation tips

With support of multi-threads replication starting from MySQL 5.7, the operations on slave are slightly different from single-thread replication. Here is a list of some operation tips for the convenience of use as below:

1. Skip a statement for a specific channel.

Sometimes, we might find out that one of the channels stop replication due to some error, and we may want to skip the statement for that channel so that we can restart a slave for it. We need to be very careful not to skip the statement from the other channel, since the command SET GLOBAL sql_slave_skip_counter = N is for global. How can we make sure the global sql_slave_skip_counter is applied to a specific channel and not to the other channel? Here are the steps:

1.1: Stop all slaves by: stop slave;

stop slave;

1.2: Set up the count of statement to skip by: SET GLOBAL sql_slave_skip_counter = N;

SET GLOBAL …
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Increasing functional testing velocity with pt-query-digest

Whenever we do upgrades for our clients from one major version of MySQL to another we strongly recommend to test in two forms.

First, it would be a performance test between the old version and the new version to make sure there aren’t going to be any unexpected issues with the query processing rates. Secondly, do a functional test to ensure all queries that are running on the old version will not have syntactic errors or problems with reserved words in the new version that we’re upgrading to.

If a client doesn’t have an appropriate testing platform to perform these types of tests, we will leverage available tools to test to the best of our ability. More often than not this includes using pt-upgrade after capturing slow logs with …

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How to Enable Binary Logging on an Amazon RDS Read Replica

One of the more common struggles I’ve had to assist with in regard to Amazon RDS is enabling binary logging on read replicas, or forming multi-tier replication in instances using version 5.6 or later after seeing that multi-tier replication is not supported in version 5.5 (for a reason that will become clear by the end of this post.)

First off, let’s have a look at the topology that I have in place in my AWS account. As you’ll see below I have a master, blog1, and a read replica that I created via the AWS console called blog2. You’ll also notice that, despite being supported, if I select instance actions while having blog2 highlighted the option to create a read replica is grayed out.

Further, if we use the MySQL CLI to connect to blog2 and check the global variables for log_bin and binlog_format, you’ll see that binary logging is off and binlog_format is set to statement. This is strange considering that the parameter …

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CPU Utilization is Not a Useful Metric

Once upon a time CPU utilization was quite a useful metric. Following are the output of several tools that provide CPU utilization metrics:

top

top reports a load of 1.66.

Is this correct? No. The correct load number is probably closer to 2.4.

# top -b -n 1| head -20
top - 11:27:45 up 151 days,  1:55,  7 users,  load average: 1.66, 1.84, 1.88
Tasks: 389 total,   3 running, 386 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.7%us, 20.6%sy,  1.2%ni, 77.3%id,  0.1%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:  32639636k total, 32206476k used,   433160k free,   235732k buffers
Swap: 16359420k total, 10285664k used,  6073756k free,  2354840k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
16702 root      20   0 8274m 5.0g 5.0g S 85.1 16.1  59164:55 VirtualBox
 4657 root      20   0  9.8g 5.2g 5.1g S 45.5 16.6  26518:13 VirtualBox
 6239 root      20   0  9.8g 5.1g 5.1g S 39.6 16.5  31200:52 VirtualBox
27070 root …
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Backup and data streaming with xbstream, tar, socat, and netcat

On April 4th 2012 Xtrabackup 2.0 was released in to GA by Percona along with a new streaming feature called xbstream. This new tool allowed for compression and parallelism of streaming backups when running xtrabackup or innobackupex without having to stream using tar, then pipe to gzip or pigz, then pipe to netcat or socat to stream your backup to the recipient server. This resulted in …

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The State of MySQL High Availability Going in to 2018

High availability for MySQL has become increasingly relevant given the ever increasing rate of adoption and implementation. It’s no secret to anyone in the community that the popularity of MySQL has become noteworthy. I still remember my start with MySQL in the early 5.0 days and people told me that I may not want to consider wasting my time training on a database that didn’t have a large industry adoption, but look at where we are now! One of my favorite pages to cite when trying to exhibit this fact is the db-engines.com ranking trend page where we can see that MySQL is right up there and contending with enterprise products such as Microsoft SQL Server and Oracle.

MySQL has gone from being part of the ever famous LAMP stack for users looking to set up their first website to seeing adoption from major technical players such as …

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Measuring the potential overhead of PMM Client on MySQL workloads

Having good historial metrics monitoring in place is critical for properly operating, maintaining and troubleshooting database systems, and Percona Monitoring and Management is one of the options we recommend to our clients for this.

One common concern among potential users is how using this may impact their database’s performance. As I could not find any conclusive information about this, I set out to do some basic tests and this post shows my results.

To begin, let me describe my setup. I used the following Google Cloud instances:

  • One 4 vCPU instance for the MySQL server
  • One 2 vCPU instance for the sysbench client
  • One 1 vCPU instance for the PMM server

I used Percona Server 5.7 and PMM 1.5.3 installed via Docker. Slow query log was enabled with long_query_time set to 0 …

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Replicating in Google Cloud SQL using Tungsten

While investigating alternatives to migrate to Google Cloud SQL, I encountered a lack of support for external masters. However, it’s possible to overcome this limitation by replicating into Google Cloud SQL using Tungsten replicator.

Cloud SQL is Google’s database-as-a-service solution, similar to RDS for Amazon Web Services. You can get a fully managed database in only a few clicks (or API calls). At the time of writing this, the only supported databases are MySQL and Postgres.

Cloud SQL alternatives

Google offers two different options for MySQL deployments.

1st generation instances:

  • Only MySQL versions 5.5 and 5.6 can provisioned
  • Max memory is limited to 16 Gb
  • Max of 250 Gb storage (up to 500 Gb with Silver or higher support package)
  • MyISAM and InnoDB
  • Asynchronous replication for read replicas

2nd generation instances:

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MySQL Crashes on DDL statement: A Lesson on purge threads

Recently there have been several issues reported to me about DDL activity causing MySQL crash scenarios. In one case it stemmed from dropping multiple databases, one after the other in rapid succession. But in the case that I was recently dealing with directly, where we were upgrading to MySQL 5.7, it was the result of mysql_upgrade running an ALTER TABLE FORCE on a 2.2Tb table in order to convert it to the new microsecond precision supporting data format.

The issue occurred after the intermediate table had been completely filled with all the necessary data and right when MySQL would swap out the existing table for the intermediate. After a period of time MySQL crashed and the following InnoDB monitor output was found in the error log.

 

2017-11-19T00:22:44.070363Z 7 [ERROR] InnoDB: The age of the last checkpoint is 379157140, which exceeds the log group capacity 377483674.
InnoDB: …

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gh-ost hooks for better visibility

In this post I will show you how to leverage Github’s gh-ost hooks for greatly improving visibility of ongoing schema changes for your organization.

One of the potential uses of gh-ost hooks is to send status updates. I will present you with some examples of how to do that via email and Slack.

What are gh-ost hooks?

gh-ost has built-in support for hooks, i.e. external scripts with predefined names, that will be called by gh-ost at certain points of a schema change operation.

The complete list is available here, but the most useful gh-ost hooks for me are:

  • gh-ost-on-startup-hook
    • called at the start of a schema change operation
  • gh-ost-on-status-hook
    • ran …
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