Some applications, particularly those written with a single-node database server in mind, attempt to immediately read a value they have just inserted into the database, without making those those operations part of a single transaction. A read/write splitting proxy or a connection pool combined with a load-balancer can direct each operation to a different database node.

Since Galera allows, for performance reasons, a very small amount of “slave lag”, the node that is processing the read may have not yet applied the write. It can return old data, causing an application that did not expect that to misbehave or produce an error.

The Solution

Through the mechanism of flow control, slave lag is kept to a minimum, but additionally Galera provides the causal wait facility for those queries that must always see the most up-to-date …

If you draw a diagram of information flow and interaction amongst teams and processes in IT, you’ll probably find that although some parts of the organization are “leaf” or “edge” nodes, the people who manage the data are not. The DBAs would usually be one of the lavender circles in the chart below, not a blue circle.

DBAs also occupy a central position in the continuum of skills:

• On one hand, they have to understand a lot about how the application code works, because application developers are their customers.

• On the other hand, they need to understand how the application runs in production, because operations staff are also their customers.

DBAs end up knowing a lot about everything, and because they can develop this all-encompassing set of skills and knowledge, the organization relies on them to do so.

Consider the old adage, “if you want to get something done, ask a busy …

Hooray for Data Structures… Where Are They?

The Key-Value Pair is my favorite programming tool. Most SQL type databases lack this feature in it simplest form. Some would argue, “Well that’s because databases don’t need dah-blah-dee-blah-blah…” Well, if they don’t need it I don’t need to write this post. :p

How many times have you found yourself asking “Why isn’t there at least simple array support!?” When you don’t want the overhead of creating a table, or a temporary table, simple data structures really do come in handy (hint, hint, nudge, nudge to all the companies producing database software with stored routine support).

I’m not one to let an apparent lack of functionality ruin my day. Instead, I add it. I had a great computer science professor who said “You don’t need pointers to create a linked list.” Then he proved it. You can create, pretty much, any abstract data structure with …

We usually try to avoid subselects because sometimes they force the use of a temporary table and limits the use of indexes. But, when is good to use a subselect?

This example was tested over table a (1310723 rows), b, c and d ( 5 rows each) and with MySQL version 5.5 and 5.6.

Let’s suppose we have a query like this:

select a.name,sum(a.count) aSum,avg(a.position) aAVG,b.col1,c.col2,d.col3
from
a join
b on (a.bid = b.id) join
c on (a.cid = c.id) join
d on (a.did = d.id)
group by a.name,b.id,c.id,d.id

What will MySQL do? First it will take the entire data set – this means that will go through each row scanning the value of  “bid,” “cid” and “did” and then apply the join to each table. At this point it has the complete data set and then it will start to cluster it, executing the sum and the average functions.

Let’s analyze it step by step:

1. Scan each row of  table a which …

The MySQL developer tools team announces 6.3.4 as our GA release for MySQL Workbench 6.3.

For the full list of changes in this revision, visit
http://dev.mysql.com/doc/relnotes/workbench/en/changes-6-3.html

For discussion, join the MySQL Workbench Forums:
http://forums.mysql.com/index.php?151

Download MySQL Workbench 6.3.4 GA now, for Windows, Mac OS X 10.7+,
Oracle Linux 6 and 7, Fedora 21 and Fedora 22, Ubuntu 14.04, Ubuntu
14.10 and Ubuntu 15.04 or sources, from:

http://dev.mysql.com/downloads/tools/workbench/

Enjoy!

Changes in MySQL Workbench 6.3.4 (2015-06-15)

…

Dear MySQL users,

The MySQL developer tools team announces 6.3.4 as our GA release for
MySQL Workbench 6.3.

For the full list of changes in this revision, visit
http://dev.mysql.com/doc/relnotes/workbench/en/changes-6-3.html

For discussion, join the MySQL Workbench Forums:
http://forums.mysql.com/index.php?151

Download MySQL Workbench 6.3.4 GA now, for Windows, Mac OS X 10.7+,
Oracle Linux 6 and 7, Fedora 21 and Fedora 22, Ubuntu 14.04, Ubuntu
14.10 and Ubuntu 15.04 or sources, from:

http://dev.mysql.com/downloads/tools/workbench/

There are many many approaches to MySQL high availability - from traditional, loosely-coupled database setups based on asynchronous replication to more modern, tightly-coupled architectures based on synchronous replication. These offer varying degrees of protection, and DBAs almost always have to choose a tradeoff between high-availability and cost. 

This is the third installment in the ‘Become a MySQL DBA’ series, and discusses the pros and cons of different approaches to high availability in MySQL. Our previous posts in the DBA series include Backup and Restore and Monitoring & Trending.

High Availability - what does it mean?

Availability is somewhat self-explanatory. If your database …

you can try to run mysql_upgrade to repair and update database medadata information. Not sure if mysql_upgrade available in mysql server 4.x or not. give it a try !!!

Relational databases are ubiquitous in OpenStack: practically every OpenStack service stores its critical metadata in a database, and the MySQL family of databases is the de-facto standard for OpenStack relational data storage. The need for high availability for these relational datastores is obvious. Galera is the default multi-master strongly-consistent replication facility for highly-available relational data in OpenStack. In this webinar, we are joined by independent OpenStack expert Florian Haas to illustrate the ins and outs of Galera for OpenStack.

Speaker bio: Florian Haas is an open source software specialist, experienced technical consultant, seasoned training instructor, and frequent public speaker. He has spoken at conferences like LinuxCon, OSCON, linux.conf.au, the OpenStack Summit, the MySQL Conference and Expo, and countless user and meetup groups across the globe.

Duration: 60 minutes

…

Why A Table of Dates?

I thought it would be nice to build on the numbers table with another very useful tool.

Dates are pretty important–especially if you are playing with data warehousing. Not only dates, but all the different properties and derived goodies contained within them. You really don’t need a dates table, unless you care about efficiency and getting to all the good stuff quickly. Perhaps I’ll showcase some of the “goodies” in later posts.

Sure, most databases have built-in functions to get everything you might want. But do you really want all the inefficiency that comes with calling functions and doing calculations over and over again? I hope not. I used the method in this article when I developed a SQL Server data warehouse for a company I worked for. It was adopted by our other SQL Server guru for all the date-sensitive stuff we did (which was a lot). It increased efficiency by leaps and …