= !MapGuide RFC 90 - Meta Tiling Support =

This page contains an change request (RFC) for the !MapGuide Open Source project.
More !MapGuide RFCs can be found on the [wiki:MapGuideRfcs RFCs] page.


== Status ==

||RFC Template Version||(1.0)||
||Submission Date||(Date/Time submitted)||
||Last Modified||(your name here) [[Timestamp]]||
||Author||Zac Spitzer, Uv ||
||RFC Status||(draft)||
||Implementation Status||(testing sandbox)||
||Proposed Milestone||(2.2)||
||Assigned PSC guide(s)||(when determined)||
||'''Voting History'''||(vote date)||
||no vote|| ||

== Overview ==

Add support internally to the MapGuide Server Engine to render larger tiles
and then slice them up into the normal tile sizes

== Motivation ==

With complex maps, it's more efficent to render one large tile than many small ones. 
There is little or no benefit for simple maps like the Sheboygan Sample.[[BR]]

Using our 140 layer example map we can observer the following timing using metatilefactor 1 & 4
and 3 different locking strategies in the attached chart MetatilingChart1.jpg.

== Proposed Solution ==

Add a meta tile factor to the tile service, which then will render larger tiles
and then slice them up into the smaller tiles which get served to clients.

== Issues ==

Locking the threads to the implicit producer consumer scheme is complex and
file locking seems not very efficient. To improve polling delay the Polling
configuration value has been changed to ms semantics so we can specify 500ms.

In addition a ace_condition has been implemented to get rid of the lockfiles 
all together and further improve the response time. (LockMethod == 3)
In addition to the standard approach with one lock per sub tile (LockMethod == 2)
we also experimented using a single file per metatile (LockMethod == 1).

== Implications ==

When using a meta tiling factor of 4, 15 tiles will wait while the meta tile is rendered
and sliced up. A most efficient locking scheme will have significant effect on this behaviour.


== Test Plan ==

The output of a tile map request should be indentical whether served 
with meta tiling enabled or without. 

== Funding/Resources ==

TBD

== Sandbox ==

http://trac.osgeo.org/mapguide/browser/sandbox/rfc90