Disable tiling when Mapserver requests layers from external WMS server

Question

We use Mapserver to create a composite of multiple layers from another WMS server. We noticed that a single request to Mapserver creates multiple requests to the "upstream" WMS server. Apparently Mapserver uses smaller tiles (that are based on the layer "SizeX" and "SizeY" config) instead of using the request bounding box it received.

E.g. incoming request to Mapserver:

And what Mapserver requests from the upstream WMS server (4 tiles):

Is there a way to disable this behavior in Mapcache? It should just use whatever bbox and resolution it got in its request for the upstream query.

We are using Mapserver 6.4.1-3~precise2 on Ubuntu but will upgrade fairly soon.

Our Mapserver config of the layer in question:

CONNECTIONTYPE UVRASTER
DATA "<GDAL_WMS>
          <Service name=\"WMS\">
              <Version>1.1.1</Version>
              <ServerUrl>http://host/wms?&amp;TIME=%TIME%&amp;PROJECTION=%2Binit%3Depsg%3A3857&amp;ENCODER=ENC1&amp;</ServerUrl>
              <SRS>EPSG:3857</SRS>
              <ImageFormat>image/png</ImageFormat>
              <Transparent>TRUE</Transparent>
              <Layers>L1</Layers>
          </Service>
          <DataWindow>
              <UpperLeftX>-20037508.34</UpperLeftX>
              <UpperLeftY>20037508.340</UpperLeftY>
              <LowerRightX>20037508.34</LowerRightX>
              <LowerRightY>-20037508.34</LowerRightY>
              <SizeX>40075</SizeX>
              <SizeY>40075</SizeY>
          </DataWindow>
          <BlockSizeX>256</BlockSizeX>
          <BlockSizeY>256</BlockSizeY>
          <Projection>EPSG:3857</Projection>
          <BandsCount>4</BandsCount>
          <DataType>Byte</DataType>
          <MaxConnections>4</MaxConnections>
          <OverviewCount>10</OverviewCount>
      </GDAL_WMS>"

Answer 1

Read http://www.gdal.org/frmt_wms.html where you see this information about BlockSizeX and BlockSizeY:

Block size in pixels. (optional, defaults to 1024, except for VirtualEarth)

If 1024 by 1024 is big enough window for your application you can just remove BlockSixeX and BlockSizeY, otherwise use as large blocks as you need.

I do not understand what does a WMS layer like this have to do with CONNECTIONTYPE UVRASTER. Could you clarify?

And while you can use GDAL for this purpose, usual way to cascading WMS with MapServer is this http://mapserver.gis.umn.edu/ogc/wms_client.html.

For your WMS server the LAYER would be something like

LAYER
  NAME "cascaded_wms"
  TYPE RASTER
  STATUS ON
  CONNECTION "http://host/wms?TIME=%TIME%&ENCODER=ENC1"
  CONNECTIONTYPE WMS
  METADATA
    "wms_srs"             "EPSG:3857"
    "wms_name"            "L1"
    "wms_server_version"  "1.1.1"
    "wms_format"          "image/png"
  END
END