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Displaying posts with tag: master-slave (reset)

How to convert master-slave to master-master replication in MySQL
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Recently, I have worked on one of this case where customer wanted to convert master-slave to master-master replication. They wanted to write on one master and keep another master as a hotspare. Many people are using this kind of environment Continue reading How to convert master-slave to master-master replication in MySQL→

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Beyond Failover: MySQL Multi-Region Master–Master Replication Considerations and Limitations.
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Standard MySQL is configurable such that a single master server can be clustered with a number of read-only slave servers. To enable this master-slave replication, master’s transaction logs are communicated to the slaves (log shipping). Log shipping is a form of asynchronous replication. Under this configuration, the data on the slave always remains behind the master, a condition referred to as slave lag or replication lag. The extent of the slave lag depends on workload, network bandwidth and network latency. Database reads can be served out of the slaves, assuming the application has been designed to …

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MySQL Benchmark – updates by primary vs secondary keys
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(Note: when I’m talking about MySQL I usually assume InnoDB storage engine. Any other case I explicitly tell this is MyISAM or Memory etc.)

I’ve heared an interesting aproach of using Master-slave replication in MySQL.

Thesis

So the theory was that since updates by primary keys are fast and by secondary keys are slow the slave has to be queried for the primary key and then run the updates by the fetched primary keys. To make this in context and more understandable:

Original query

UPDATE table_for_test SET value_to_change = 123 WHERE cond_column_1 = 987 AND cond_column_2 > 765; …
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Sleeping connections
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Why is it so important to close connections to databases if there’s no explicit need to keep them open (which usually the case)?

Symptoms

  • Icinga reports high usage of allowed connections (>90%) on master MySQL server.
  • No running queries or any specific in processlist. All the connections are sleeping from the same servers.
  • The number of connections was 20 times more than the usual

Root cause

There was tremendous amount of queries doing “copying to tmp table” on the slaves. The connections were opened to both master and slaves and waiting for the slaves to answer the query the connections …

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Making mk-table-checksum less intrusive
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About a month ago I needed to compare tens of thousands of tables in hundreds of databases between a few different servers. The obvious choice was, mk-table-checksum! The only problem was, that the tool needs to know the minimum and maximum value of the column by which each table is to be subdivided into chunks and checksummed. This select min(col), max(col) from table locks all write operations on the table and on a big table it meant downtime.

Looking at the source it was clear we could make mk-table-checksum run the select min(col), max(col) from table on the read-only slave and use the values to checksum the master.

It was …

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Setting up Master-Slave Replication with MySQL
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Replication enables data from one MySQL server to be replicated on one or more other MySQL servers. Replication is mostly used as scale-out solution. In such a solution, all writes and updates take place on the master server, while reads take place on one or more slaves. This model is actually known as master-slave replication and this is the kind of replication that I will be setting up in this post.

Showing entries 1 to 6

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