Month: February 2013

Merging tables with INSERT…ON DUPLICATE KEY UPDATE

MySQL

Had a case recently where I had to merge data from two identically structured tables containing nearly identical data.

“Nearly identical” meaning most table data is identical in both; sometimes a row is missing from one of the tables; sometimes same row (according to PK) appears in both, but some columns are NULL is one tables (while others can be NULL in the second).

Otherwise no contradicting data: it was not possible for some data to be “3” in one table and “4” in the other.

How do you create a merge of the tables, such that all missing rows are completed, and NULLs replaced by actual values when possible?

pt-table-sync comes to mind: one can do a bidirectional syncing of two tables, and actually stating how to resolve ambiguities (like “greater value wins”). Very powerful! An example would be:

pt-table-sync --bidirectional --conflict-column=a --conflict-comparison=greatest --tables ...

However I didn’t actually have any problem with the tables themselves. The two tables were just fine as they were; missing or NULL data does not indicate an error on their part. I wanted to get their merge. pt-table-sync is still up for the job: we can duplicate them, merge on the copy… But I prefer a query over an external script when possible.

INSERT…ON DUPLICATE KEY UPDATE

This MySQL-specific syntax is actually quite powerful. It basically says “if the insert fails due to unique constraint, you get a chance to update the row causing the failure”. But it also allows for smart setting of the column via the VALUES() clause. Let’s present some sample data and then see the solution. Continue reading » “Merging tables with INSERT…ON DUPLICATE KEY UPDATE”

MySQL Stored Routines Debugger & Debugging API: sneak preview video

MySQL

This is a sneak peek video introduction/preview of an in-development free and open source server side debugger & debugging API for MySQL stored routines.

MySQL does not provide server side debugging capabilities for stored routines. Some tools exist, including MySQL’s own, that assist in stored routine debugging. These are all GUI based and, to the best of my knowledge, MS Windows based. There is one solution in alpha stage that is developed for Java/eclipse; I did not look at the code. See discussion here and here.

An ideal solution would be to have debugging API in the server itself – independently of your client, programming language or operating system. To the best of my knowledge, nothing like that is being developed.

I’m now presenting a rdebug: a stored routines server-side debugger, Pure-SQL, based on stored routines. rdebug is developed as part of common_schema, and actually relies on some of its power.

Like some other tools, it uses code injection and manipulation: it injects debugging info into your stored routine. You need to “compile” your routine with debugging info.

Unlike some other tools, it actually runs your stored routines. It does not mimic or simulate them on client side. It does not break them into smaller routines, attempting to assemble the original behavior from lego bricks.

The quick technical overview is that you use two processes (MySQL threads): the worker process running the routine (your natural call my_routine()), and the debugger process. The debugger process attaches itself to the worker process; it controls the worker by commands like “step over”; it gets data from the worker: what’s the current stack trace? What variables are now available and what are their values?; it manipulates the worker’s data: it can utilize breakpoints to modify worker’s local & session variables. Continue reading » “MySQL Stored Routines Debugger & Debugging API: sneak preview video”

Win a free Percona Live 2013 pass — unveiling riddle hints

MySQL

Apparently my first attempt at rhyming proved to be unsuccessful: only two courageous men attempted solving the riddle. As I’m pretty sure a free pass would appeal to many, and I do have a few readers for my blog, I must conclude my riddle was just too hard. Obscure, perhaps.

Hope I didn’t scare anyone off. Without further ado I present some hints. This post will update with more hints as the day progresses — please refresh to see changes. I start with two hints.

But first, recap of the riddle:

Who will open your present,

Make you play pleasant,

Tidy your mess,

Do the same for all else?

It has something to do with the MySQL world. Continue reading » “Win a free Percona Live 2013 pass — unveiling riddle hints”

Sessions of interest in Percona Live 2013

MySQL

Percona Live 2013 is shortly upon us, and it might be a good idea to watch for what’s ahead of us.

Talks of interest

There is no way I can do justice to all. I wish to point out a small number of sessions I am personally interested in attending. I will not be able to attend them all, since there are too many sessions of interest and too few instances of myself (merely one).

I’ve tried to list some talks which are not absolutely obvious (when Peter Zaitsev speaks of MySQL performance, or Monty speaks about MariaDB, or Robert Hodges or Domas speak about replication — well — you’re certain to have the ins and outs, right?). I can also expect Galera or Percona XtraDB Cluster talks to attract a lot of attention. There is a lot of good content for each.

But I was happy to find some very special talks this year, which are not the “every conference has got to have one talk about this” type. Here’s a hybrid collection of both types.

After constructing the list I’ve intentionally dropped two random sessions. If you are speaking, and not mentioned here, your talk must be one of those two! Continue reading » “Sessions of interest in Percona Live 2013”