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 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.

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