[Tilesathome] MySQL and iowait

[Lars Aronsson]

Frederik Ramm wrote:

> > Earlier today, t at h ran like a dream.  Frederik disabled the "replace"
> > queries for zoom level 13-17, apparently starting at 14:00 BST.
> 
> I disabled them in the SVN version of the server code. I have no 
> idea if and when that code went into production. OJW has 
> resurfaced and posted a number of

I was wrong in guessing that your change had gone into production.  
It hadn't.  Instead, for some reason unknown to me, the MySQL 
server had stopped.  This made uploads go a lot faster, which I 
thought was a bonus, but OJW thought was a security risk.  :-)

Let's hope no evil people explored this window of exposure.  
Anyway, it gave us a clear idea of what uploads might be like if 
metadata update was faster.

The t at h system now has two bottlenecks: One is the slow updating 
of metadata for each little tile.  I think we're about to find a 
solution for that.  The other is OJW's absense during weekdays for 
the last two weeks.  We can hope that this will improve, but 
unless we pay him a decent salary we can't really force him.  We 
should regard people just the same as computer systems, by 
applying basic queueing theory: Don't build queues.  If a todo 
list is longer than 5 items, just don't add more items.  Don't 
flood OJW with new ideas before we can solve the "batch upload" 
thing.  Be economic.  Get things finished.


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se