It’s not uncommon to promote a server from slave to master. One of the key things to protect your data integrity is to make sure that the promoted slave is permanently disconnected from its old master. If not, it may get writes from the old master, which can cause all kinds of data corruption. MySQL provides the handy RESET SLAVE command. But as we’ll see, its behavior has changed along with the MySQL versions and it’s easy to shoot yourself in the foot if you use it incorrectly. So how do you safely disconnect a replication slave?

In short

• For MySQL 5.0 and 5.1, run STOP SLAVE, CHANGE MASTER TO MASTER_HOST='' and then RESET SLAVE.
• For MySQL 5.5 and 5.6, run STOP SLAVE and then RESET SLAVE ALL.
• For all versions, ban master-user, master-host and master-password settings in my.cnf, …

Importing a text file containing a list of SQL commands into MySQL is a straightforward task. All you need to do is simply feed the file contents through pipe into MySQL command line client. For example: mysql app_production < dump.sql.

The reasons for doing such imports can be very different - restoring MySQL backups created with mysqldump, manually replaying binary log events or performing database migrations during software roll-outs.

While the task is simple, the import may not end successfully and when this happens, how to tell what the problem was?

MySQL errors

Whenever database hits an error, MySQL produces an error message that describes the problem and the import process stops immediately. If the message is not clear enough, you can always refer to the reported line number, which is the line number inside the source SQL file. This way you can locate the precise command or query that …

Percona is glad to announce the release of Percona XtraDB Cluster 5.5.30-23.7.4 for MySQL on April 17, 2013. Binaries are available from the downloads area or from our software repositories.

New Features:

• Percona XtraDB Cluster has implemented initial implementation of weighted quorum. Weight for node can be assigned via pc.weight option in the wsrep_provider_options variable. Accepted values are in the range [0, 255] (inclusive). Quorum is computed using weighted sum over group members.
• …

The MySQL team at Oracle are excited to announce the immediate availability of the second MySQL Cluster 7.3 Development Milestone Release (DMR). Some might call MySQL Cluster 7.3 "the foreign keys release" - and sure enough it is a major engineering achievement to build a distributed database that enforces referential integrity across a shared-nothing cluster, while maintaining ACID compliance and cross-shard JOINs. But MySQL Cluster 7.3 is so much more as well. The design focus has been on enabling developer agility - making it simpler and faster than ever to enhance new services with a highly scalable, fault tolerant, real-time database - with minimum development or operational effort.

You should probably read Marc Alff’s post about configuring Performance Schema in MySQL 5.6.

We wrote another guide, how to start using user/table/index statistics first introduced in Google patch, now part of various MySQL branches and forks:

1. Start MySQL

From time to time I will observe servers wasting lots of CPU when doing batch row operations. In perf top it will look like this:

8.24% mysqld [.] Arg_comparator::compare_int_unsigned()
7.17% mysqld [.] Item_cond_and::val_int()
4.37% mysqld [.] Item_field::val_int()
4.37% mysqld [.] Item_cond_or::val_int()
2.90% mysqld [.] MYSQLparse(void*)
2.64% mysqld [.] Item::val_bool()

Essentially if you construct queries like (a=1 AND b=2) OR (a=3 AND b=4) ..., at large enough batch size evaluating the WHERE will become far more expensive than anything else (yes, more expensive than decompressing rows or doing all the InnoDB magic and what not).

MySQL has awesome syntax that makes certain batch lookups much faster: WHERE a IN (1,2,3). It constructs a tree that then each row can be compared against and one does not have to iterate through lists of predicates to check whether the row returned by batch index lookups …

Read the original article at How to make MySQL multi-master work for you

Coming soon! Want more? Grab our Scalable Startups monthly for more tips and special content. Here’s a sample Related posts:Transaction isolation breaks when writing two masters MySQL requires an authoritative master to build slaves MySQL needs single master to check data integrity A master isn’t born but made Why does MySQL replication fail?

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Read the original article at MySQL needs single master to check data integrity

MySQL slaves can drift out of sync. Many of our clients are surprised to find some data differences in their replication topology, once we do some checking and sniffing around. Such checks require a single reliable or authoritative master to compare against. Click through to the end for multi-master solutions that work with MySQL. Reason [...]

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1. MySQL requires an authoritative master to build slaves
2. …

Read the original article at MySQL requires an authoritative master to build slaves

In MySQL database operations, you often need to rebuild slaves. They fail for a lot of different reasons, fall out of sync or crash. When this happens you may find you need to reclone and start fresh. This is normally done by finding your authoritative master database, and doing a hotbackup. Click through to the [...]

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1. Limitations of MySQL row-based replication
2. …

Read the original article at Limitations of MySQL row-based replication

MySQL offers a few different options for how you perform replication. Statement-based has been around a lot longer, and though it has some troublesome characteristics they’re known well and can be managed. What’s more it supports online schema changes with multi-master active-passive setup. We recommend this solution. Row-based replication is newer. It attempts to address [...]

For more articles like these go to Sean Hull's Scalable Startups

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1. Why does MySQL replication fail?
2. …