MapGuide RFC 64 - Enabling strict exception handling for tile generation

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	(08.05.2009)
Last Modified	(UV Wildner) Timestamp
Author	(UV Wildner)
RFC Status	(draft)
Implementation Status	(discussion needed)
Proposed Milestone	(2.1)
Assigned PSC guide(s)	(when determined)
Voting History	(vote date)
+1
+0
-0
-1
no vote

Overview

Currently an exception thrown during the stylization code for a tile is caught and ignored. This can lead to partially incomplete tiles which are hard to detect as no error information is passed via the API. Even worse the tile is kept in the tilecache!

Motivation

Originally, the mapguide server has been designed as an interactive map generation system. For the important use case of rendering tiles and filling the tile cache incomplete tiles are undesirable. in particular keeping the faulty tile in the cache seems the wrong way to go.

Proposed Solution

A switch in serverconfig.ini should be introduced which can change this behaviour on demand. e.g. HandleRenderingErrors = STRICT

which leaves us room for additional ways to deal with this:

render a tile with an error message could be

HandleRenderingErrors = SHOW

default cases

HandleRenderingErrors = IGNORE

HandleRenderingErrors = DEFAULT

HandleRenderingErrors =

and ommitting the parameter would change nothing

However I think letting the tile into the cache should be generally prohibited in an exception situation.

Implications

NONE

Test Plan

Render tiles on a low memory virtual machine which causes memory errors and compare TileCache with different settings

Funding/Resources

closed Issues

NONE

open Issues

Does anyone wants to have faulty tiles in the tile cache?