[mapserver-users] Mapcache - best way to find broken or white tiles in a service?

[Travis Kirstine]

You shouldn't have any cached "broken" tiles unless your source WMS is
generating the white images (metatiles).  I believe MapCache will generate
a 404 and return a empty tile if configured.  This may be the white tiles
you are seeing.

   <!-- errors
        configure how error will be reported back to a client:
          - log : no error is reported back, except an http error code.
          - report : return the error message to the client in textual
format
          - empty_img : return an empty image to the client. the actual
error code is in the X-Mapcache-Error http header
          - report_img : return an image with the error text included
inside. not implemented yet.
        the default setting is to report the error message back to the
user. In production, you might want to set this to "log"
        if you're paranoid, or to "empty_img" if you want to play nice with
non-conforming clients.
   -->
   <errors>report</errors>

It can be very difficult to locate and clean up tiles from a cache, the
easiest method and in some cases the fastest is simply to create a new
cache and delete the old one.  One alternative is to use the mapcache_seed
command line tool to either -f force the creation of new tiles or use the
-mode delete option to delete the tiles from the cache.  BTW you can use a
polygon (shapefile) with mapcache_seed to only update / delete the desired
area using the -d flag.

Also if you are using a disk cache you might be using symlinks which will
allow mapcache to "reuse" blank tiles.  If this is the case you might need
to find / delete the symlinks rather than a "file"

<cache name="disk" type="disk">
   <!-- base
        Absolute filesystem path where the tile structure will be stored.
        This directory needs to be readable and writable by the user running
        Apache.
   -->
   <base>/tmp</base>
   <!-- symlink_blank

*        Enable blank (i.e. uniform color) tile detection. Blank tiles will
be*
*        detected at creation time and linked to a single blank tile on
disk*
*        to preserve disk space.*
   -->
   <symlink_blank/>
</cache>



On Tue, 19 Feb 2019 at 16:47, Mark Volz <MarkVolz at co.lyon.mn.us> wrote:

> Hello,
>
>
>
> On my webmap I noticed a few broken (white) tiles in a single area from my
> mapcache server.  I would like to know the best way to find broken tiles in
> my mapcache service.
>
> ·         Initially I was concerned that I would need to the tile number
> and folder location by using the BBOX, WIDTH, and TILE RESOLUTION from the
> request.  However, I figured out using the mapcache demo is easier to work
> with /mapcache/demo/
>
> ·         Would it be better just to delete any tile that is 1K or
> smaller?  These problibly are tiles that are broken, or intended to be
> blank in the first place.
>
> ·         What do others do to validate that the mapcache tiles have been
> built appropriately?
>
> Thanks!
>
>
>
> Sincerely,
>
> *Mark Volz, GISP*
>
> *Lyon County GIS Coordinator*
>
>
> _______________________________________________
> mapserver-users mailing list
> mapserver-users at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/mapserver-users
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