Comments on: Stored Function to generate Sequences

By: Using Multiple Sequences in a Table « Everything MySQL

Using Multiple Sequences in a Table « Everything MySQL — Tue, 16 Sep 2008 18:32:21 +0000

[...] issues. After lot of trials, debates and finally referring Planet MySQL, I went ahead with this suggestion by Peter from MySQL Performance Blog and some help from here. CREATE TABLE sequences ( event_id [...]

By: Justin Huff

Justin Huff — Thu, 31 Jul 2008 01:22:16 +0000

I typically see the update step written like:
UPDATE sequence SET nValue=last_insert_id(nValue+1) WHERE strName=?

I’d like to allow servers the option of asking for more than one id per call by moving the increment step outside the last_insert_id:
UPDATE sequence SET nValue=last_insert_id(nValue)+? WHERE strName=?

The value in the table shifts from being the ‘last id handed out’ to ‘the next id to hand out’. That way requesters don’t need to know how big the last block was.

Am I missing something here?
Thanks!

By: Links for Wed 7 May 2008 - Joseph Scott’s Blog

Links for Wed 7 May 2008 - Joseph Scott’s Blog — Thu, 08 May 2008 16:52:56 +0000

[...] Stored Function to generate Sequences | MySQL Performance Blog - You could combine this with an INSERT trigger and get even more auto_increment like functionality. Tags: database mysql sequence [...]

By: peter

peter — Fri, 04 Apr 2008 01:41:33 +0000

Arjen,

Indeed insert on dup key updates saves you from initialization though I’m wondering what way would be the faster.
Though I guess there would not be any significant difference here.

By: Arjen Lentz

Arjen Lentz — Fri, 04 Apr 2008 01:36:52 +0000

kL, even with a sequence generator stored in MyISAM you would not see the same number in different threads.

By: Arjen Lentz

Arjen Lentz — Fri, 04 Apr 2008 01:34:58 +0000

Here was mine http://arjen-lentz.livejournal.com/34627.html (been there for a few years
Also incorporates a trigger so the app can be oblivious it’s not an AUTO_INCREMENT column.

By: peter

peter — Thu, 03 Apr 2008 15:17:17 +0000

kL,

Yes you can use char here or even better ENUM or INT if you’re hunting for last 0.01% of performance.

Regarding Innodb Tables it still works because updates to the same rows will be serialized and so you can’t get same values in different threads.

By: Toby

Toby — Thu, 03 Apr 2008 14:19:43 +0000

This technique is perfectly safe with InnoDB tables.

By: kL

kL — Thu, 03 Apr 2008 09:49:15 +0000

If you change sequence name from varchar to char you’ll get fixed-width table (slightly faster).

It’s probably important that sequences are in MyISAM table that doesn’t support transactions - otherwise different threads would be isolated (I in ACID) and could come up with the same sequence value!