MySQL-dump - SQL

Innodb cache preloading using blackhole

kris@koehntopp.de (Kristian Köhntopp) — Fri, 15 Jun 2007 12:52:54 +0200

In MyISAM, we do have LOAD INDEX INTO CACHE. In InnoDB this does not work. For benchmarking I often require a way to preload the innodb_buffer_pool with the primary key and data after a server restart to shorten warmup phases.

According to Blackhole Specialist Kai, the following should work:

CODE:

mysql> create table t like innodbtable;
mysql> alter table t engine = blackhole;
mysql> insert into t select * from innodbtable;

Another win for the unbreakable BLACKHOLE storage engine.

PROCEDURE execute

kris@koehntopp.de (Kristian Köhntopp) — Mon, 19 Jun 2006 12:52:30 +0200

Many maintenance procedures need to generate SQL as strings, and then need to execute that string as SQL. Use PREPARE for this.

CODE:

CREATE DATABASE `admin`;
USE admin

CREATE PROCEDURE `execute`(in cmd text)
SQL SECURITY INVOKER
begin
  set @x = cmd;
  prepare x from @x;
  execute x;
  drop prepare x;
end

(as requested on Freenode:#mysql)

Triggers maintaining summaries

kris@koehntopp.de (Kristian Köhntopp) — Wed, 25 Jan 2006 19:47:10 +0100

Frank asked in Can MySQL triggers update another table just that.

Here is how to have a users table with a summary field, and a detail table with a value field. When records are inserted, modified or deleted with changing values in the detail table, the matching summaries in the users table are updated.

Continue reading "Triggers maintaining summaries"

The Quota Query and Running Sums by Jan and Kai

kris@koehntopp.de (Kristian Köhntopp) — Sun, 18 Dec 2005 20:35:14 +0100

Last week I was with a customer and came across a side problem that was of a more general nature. It is the problem of users having a number of things that use up ressources. The things may be mails, recordings, stamps or whatever - for simplicity we assume recordings, and the ressource consumed is size. The system has a quota system in place, which stores a ressource limit per user.

The quota problem is: if a user is over quota, we want to get a number of item ids to delete per user from old to new, until that user is under quota or just one item over quota. This is the quota problem, and I needed a quota query that solves it.

Here is the setup.

Continue reading "The Quota Query and Running Sums by Jan and Kai"

Exploring stored procedures: Eratosthenes

kris@koehntopp.de (Kristian Köhntopp) — Wed, 30 Nov 2005 09:21:19 +0100

The sieve of Eratosthenes finds prime numbers by creating a list of numbers, taking the smallest number in this list that is not stroken out and striking out all of its multiples, then going on to the next number that is not stroken out and so on.

For example, if the starting list is (2, 3, 4, 5, 6, 7, 8, 9) (we do leave out 1, because it is not a prime), then the first number from the list is 2, and therefore 4, 6 and 8 cannot be primes and are removed from the list: 2 is prime, and the list is now (3, 5, 7, 9). Lowest number from the list is 3, and therefore 6 and 9 cannot be primes, leaving (5, 7) and so on.

Continue reading "Exploring stored procedures: Eratosthenes"

A graph problem

kris@koehntopp.de (Kristian Köhntopp) — Thu, 22 Sep 2005 13:27:28 +0200

At work, I came across an interesting problem involving graphs for which I found no completely satisfactory solution.

A colleague tried to model applications and their dependencies as a directed graph. When editing dependencies for a given node, he wanted to show only nodes as new possible descendants which are not yet direct descendants of the current node. Additionally, when selecting new parents, nodes that are already direct parents should not be shown. Since he is still on MySQL 4.0, subselects could not be used.

Here is the data model and a bit of test data:

Continue reading "A graph problem"

Nermalisation

www@azundris.com (Azundris) — Mon, 12 Sep 2005 00:44:00 +0200

An introduction to the normalisation of databases that requires no prior knowledge and serves as an excuse to introduce cat content into MySQL-dump.
German version

Continue reading "Nermalisation"

A day in the docs

www@azundris.com (Azundris) — Fri, 09 Sep 2005 08:31:00 +0200

The most recent MySQL server I used in a production environment was a 3.23, so in conjunction with reading the 5.0 sources, I saw fit to reread large parts of the documentation to see where updates had happened, fixes were applied, extensions added. Here are some random clippings from the docs that illustrate quirks, changes from MySQL 3.23 (other than those noted in 3.23->4.0, 4.0->4.1, 4.1->5.0 which we'll give a brief tour of at the end) and differences from the standard. If you recently read the docs, kindly walk on, there's nothing to see here. If being a MySQL admin is #96 on the list of who you are, stand by for some trivia.
Continue reading "A day in the docs"

SQL-Zoo interactive tutorial

www@azundris.com (Azundris) — Fri, 02 Sep 2005 08:26:35 +0200

By chance, I came across this interactive interactive SQL tutorial — select your preferred engine, create queries for a variety of exercises, see the results online immediately. Instructive for the beginner, possibly fun for the advanced. : )