I continually see consulting engagements like the following: My server load is high and my queries are slow and my server crashes. Can you help me tune my server? Here is the my.cnf: [mysqld] sort_buffer_size = 100M Such a large sort_buffer_size is a serious problem, but unfortunately there is a lot of cargo cult advice on the Internet, in books, and in “tuning scripts,” that perpetuates the harmful advice to increase it.

One of the big "Selling Points" of MySQL is support for Multiple Storage engines, and from the glance view it is indeed great to provide users with same top level SQL interface allowing them to store their data many different way. As nice as it sounds the in theory this benefit comes at very significant cost in performance, operational and development complexity. Let me touch just on the few complications it brings in

Conversions - Each storage engine has its own data storage format so MySQL has to do a lot of copying and conversions while accessing the data, which significantly limits performance compared to basically "zero copy" design one may have streaming data from memory when it fits there.
Optimizer and Execution Storage engines are not created equal especially if you look at In Memory storage engines vs Distributed ones. Trying to handle all different cases in Optimizer - such as in memory …

Few years ago I was looking at crash recovery code, and realized that InnoDB has removed all the comments from the code [this assumption is debunked by Heikki in comments section], related to replay of transaction log. Judging by high quality of comments in the remaining codebase, I realized that it was all done to obscure any efforts to build another InnoDB hot backup solution – competitor to first Innobase standalone offering.

I was enjoying the moment when Percona launched their own implementation of the tool. Since the inception, it became more and more robust and feature rich.

We have used xtrabackup in our environment a lot – just… not for backup – the major use case right now is for cloning server instances – either for building new replicas, shadow servers, or …

Answering questions asked on the site.

Ivo Radev asks:

I am trying to make a very simple query.

We have a log table which different machines write to. Given the machine list, I need to find the latest log timestamp.

Currently, the query looks like this:

SELECT  MAX(log_time)
FROM    log_table
WHERE   log_machine IN ($machines)

, and I pass the comma-separated list of $machines from PHP.

The weird thing is that the query is literally instant when there is only one machine (any) in the list but slow when there are multiple machines.

I’m considering doing it in separate queries and then process the results in PHP. However I’d like to know if there is a fast solution in MySQL.

Most probably, there is a composite index on (log_machine, log_time) which is being used for the query.

Usually, a query …

Our Universe is full of ironies. But some ironies are just too hard to take.

As you may have guessed (!!!), I am an avid Linux developer and user. Though once upon a time I did develop under Windows. Yes, believe it. And on one particular case, I got to be on a first-name basis with some of the Microsoft Software Engineers to resolve issues we were having with their OLE crap — what the Holy Gods of Microsoft decided to redub as “Active-X”.

But I digress. For the past 10 years, I have been solid Linux and have defenestrated Windows for the most part. But as you know, you can never really completely eliminate Windows.  Despite your best efforts, it will always be (for now, at least) the 500 pound gorilla in any room you care to be in. The installed software base there is just staggering, and most have no Linux options.

But then that’s why projects like Wine and the many wonderful hypervisors …

Good article. I like this . In meantime I did similar app in order to solve this transition. Keep posting.

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If your MySQL server has hundreds of clients (applications) and tens of thousands of queries per second,  MySQL default network settings may NOT be for you.  Network performance is not often a significant factor in the performance of MySQL.  That said, there are things to consider.

If you are building new applications make these changes now.  Developer expectations are hard to change.  My example below will break your application if  developers open a database connections and then spend ten minutes playing with their play doe before making a query.  If you have working applications …

As the program chair for the recently announced MySQL Track at the ODTUG Kaleidoscope conference located in Washington DC we are also looking into an associated free community event for MySQL locals in addition to a dedicated track for 4 days.

Please let us know your name and email via the form at http://ronaldbradford.com/ODTUG/free-event/ so we can provide more details in the coming week as we try to finalize logistics.

Registration will be necessary for attendance however for now we just want to know who is local so we can provide more details soon!

Updated. Full details of the free Monday night sundown sessions and reception can be found at MySQL track with free event at …

I frequently encounter MySQL servers with intermittent problems that don’t happen when I’m watching the server. Gathering good diagnostic data when the problem happens is a must. Aspersa includes two utilities to make this easier.

The first is called ’stalk’. It would be called ‘watch’ but that’s already a name of a standard Unix utility. It simply watches for a condition to happen and fires off the second utility.

This second utility does most of the work. It is called ‘collect’ and by default, it gathers stats on a number of things for 30 seconds. It names these statistics according to the time it was started, and places them into a directory for analysis.

Here’s a sample of how to use the tools. In summary: get them and make them executable, then configure them; then start a screen session and run the ’stalk’ utility as root. Go do …

[author's note: personally, I use awk a bunch in MySQL DBA work, for tasks like scrubbing data from a production export for use in qa/dev, but usually have to resort to Perl for really complex stuff, but now I know how to do .]

Basics:
By default, fields are separated by any number of spaces. The -F option to awk changes the separator on commandline.
Print the first field, fields are separated by a colon.
awk -F: '{print $1}' /etc/passwd

Print the first and fifth field:
awk -F: '{$print $1,$5}' /etc/passwd

Can pattern match and use files, so you can replace:
grep foo /etc/passwd | awk -F: '{print $1,$5}'
with:
awk -F: '/foo/ {print $1,$5}' /etc/passwd

NF = built in variable (no $) used to mean “field number”
This will print the first and last fields of lines where the first …