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Displaying posts with tag: pt-table-checksum (reset)
Troubleshooting Data Differences in a MySQL Database Cluster

Overview The Skinny

From time to time we are asked how to check whether or not there are data discrepancies between Master/Slave nodes within a MySQL (or MariaDB) cluster that’s managed with Tungsten Clustering. This is always a challenging task, not least because we hope and believe that our replication mechanism would avoid such occurrences, that said there can be factors outside of our control that can appear to “corrupt” data – such as inadvertent execution of DML against a slave using a root level user account.

Tungsten Replicator, the core replication component in our Tungsten Clustering solution for MySQL (& MariaDB), is just that, a replicator – it takes transactions from the binary logs and replicates them around. The replicator isn’t a data synchronisation tool in that respect, the …

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Caveats With pt-table-checksum Using Row-Based Replication, and Replication Filters

As per the documentation, pt-table-checksum is a tool to perform online replication consistency checks by executing checksum queries on the master, which produces different results on replicas that are inconsistent with the master.

The master and each slave insert checksums into the percona.checksums table, and these are later compared for differences. It’s fairly obvious that the checksums need to be determined independently on each node, and so these inserts must be replicated as STATEMENT and not ROW. Otherwise, the slaves would just insert the same checksum as the master and not calculate it independently.

The tool only requires


  for its own session. It sets this itself on the master, but will error if this isn’t already set on each slave node. The …

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How to check and fix MySQL replication inconsistencies ?

There are several possibilities to end up with inconsistent MySQL replication, This could be accidental or intentional. In this blog I would like to discuss on how to identify the inconsistent slaves with master and fix them. I used here pt-table-checksum (to find the difference between master and slave) and pt-table-sync (to sync. between MySQL master and slave) from Percona Toolkit, The detailed documentation of Percona toolkit is available here for your reference. I expect / recommend you to be careful (as I mentioned above, sometimes records are inserted / deleted on MySQL slave intentionally) before using pt-table-checksum to sync. slave with master because rollbacking this task is even more expensive. The objective of this blog is to show you how to find differences between master and …

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How to Handle pt-table-checksum Errors

In this blog post, we’ll look at how to approach pt-table-checksum errors.

pt-table-checksum is one of the most popular tools in Percona Toolkit, and it is widely used to identify data differences between masters and slaves. Therefore, as Percona Support Engineers we have customers often asking questions related to the pt-table-checksum errors and warnings produced. Below are the most common issues raised with pt-table-checksum, and we decided to address those issues to help with how to mitigate related warnings or errors.

Unable to detect …

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Fixing Broken MySQL Replication: Basic Usage of pt-table-checksum, pt-slave-restart and pt-table-sync

For second day in a row I am trying to concentrate on writing a second issue for my new series of blog posts, but I can not complete. It seems half of it is going to be devoted to three tools from Percona Toolkit that I had to remember and explain this week: pt-table-checksum, pt-table-sync and pt-slave-restart. So, I decided to write a separate post on this topic.

The context was simple: in the middle of (the weekend) night customer comes with broken replication issue, without a fresh backup from master or with few gigabytes …

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Show differences found by pt-table-checksum

pt-table-checksum perfectly solves problem of checking if master and its slaves are in-sync. It answers the question “Are the slaves consistent with the master?”. However if the answer is “No” pt-table-checksum doesn’t actually tell what exactly is different. [crayon-59f9aff300dfa915077909/] pt-table-sync may give a partial answer. It can print SQL statements to sync the replication cluster. Reading the SQL […]

The post Show differences found by pt-table-checksum appeared first on TwinDB.

MySQL replication primer with pt-table-checksum / pt-table-sync, part 2

This is the second and last tutorial blog post on how to use pt-table-checksum / pt-table-sync tools for MySQL replication.

In the first post, I showed you how to use the




  tools in a typical MySQL replication setup. In this post, we’ll discuss MySQL replication for more advanced topologies. I will show you how to use these tools in a chained …

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Syncing Inconsistent MySQL Slaves


Checksum is a standard practice among DBAs to verify the data consistency across replicated nodes. In this post we’re going to review the syncing options for an inconsistent MySQL slave of Galera cluster node.

Here we’re assuming a setup of regular replication to a MySQL instance from one of the Galera cluster nodes.

In the usual MySQL replication setup, standard practice involves the usage of the pt-table-checksum tool to identify the discrepancies and usage of pt-table-sync to bring them in sync. The checksum tool, pt-table-checksum, can run across Galera cluster node to verify the data consistency and confirm if the MySQL slave is consistent with a chosen primary node.

What happens if this Galera cluster’s regular MySQL slave sees data inconsistency on it? Will pt-table-sync work there? The answer to this depends…
pt-table-sync when used with –sync-to-master …

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MySQL replication primer with pt-table-checksum and pt-table-sync

MySQL replication is a process that allows you to easily maintain multiple copies of MySQL data by having them copied automatically from a master to a slave database.

It’s essential to make sure the slave servers have the same set of data as the master to ensure data is consistent within the replication stream. MySQL slave server data can drift from the master for many reasons – e.g. replication errors, accidental direct updates on slave, etc.

Here at Percona Support we highly recommend that our customers periodically run the pt-table-checksum tool to verify data consistency within replication streams. Specifically, after fixing replication errors on slave servers to ensure that the slave has identical data as its master. As you don’t want to put …

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Keep your MySQL data in sync when using Tungsten Replicator

MySQL replication isn’t perfect and sometimes our data gets out of sync, either by a failure in replication or human intervention. We are all familiar with Percona Toolkit’s pt-table-checksum and pt-table-sync to help us check and fix data inconsistencies – but imagine the following scenario where we mix regular replication with the Tungsten Replicator:

We have regular replication going from master (db1) to 4 slaves (db2, db3, db4 and db5), but also we find that db3 is also master of db4 and db5 using Tungsten replication for 1 database called test. This setup is currently working this way because it was deployed some time ago when multi-source replication was not possible using regular MySQL replication. This is now a working feature in …

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