Query in a loop slows down over time

Discussion of open issues, suggestions and bugs regarding ADO.NET provider for MySQL
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Joined: Mon 26 Jul 2010 23:29

Query in a loop slows down over time

Post by realtytrends » Tue 19 Apr 2011 15:15

I have tried to figure it out for a whole day but have no clue. Really hope can get some help here. The following is the code that I am having trouble with. ZoomedPixelCoordinateSet is the representation of a stored procedure. The query version of this just dog slow so I made a stored procedure. I am pulling 50 records each time.

public List GetZoomedTileCoordinates(
short zoom, int skipNum, int takeNum)
List list = new List();
using (RTMySQLInternetEntities ircontext = new RTMySQLInternetEntities())
ircontext.CommandTimeout = 300;
var zoomedList = (from z in ircontext.ZoomedPixelCoordinateSet
where z.Zoom == zoom
orderby z.GTileY
select new { z.Zoom, z.GTileX, z.GTileY }).Distinct().OrderBy(o => o.GTileY).ThenBy(o => o.GTileX).Skip(skipNum).Take(takeNum);
foreach (var i in zoomedList)
ZoomedTileCoordinates ztc = new ZoomedTileCoordinates();
ztc.Zoom = i.Zoom;
ztc.TileX = i.GTileX;
ztc.TileY = i.GTileY;
catch (Exception ex)
string str = ex.Message;

return list;
It starts fast. But after a while the eval to zoomedList become very slow. It took about minute and half to come back. Any idea?

Thanks so much!


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Posts: 2919
Joined: Mon 07 Jul 2008 13:16

Post by AndreyR » Wed 20 Apr 2011 14:45

The reason is the MySQL server LIMIT behaviour. Take a look at this thread on MySQL forums, for example.

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