[Mapserver-users] Whole lotta shakin' going on

[Thorsten Fischer]

On Fri, 2003-09-05 at 13:59, Ed McNierney wrote:

[ tips on serving raster data ]
> 1. Make sure you have resampled the imagery (if necessary) so
> small-scale (zoomed-out) views use a data source with input resolution.

1. a) for simple 'intro' type of pages you might even want to consider
static images (.png for example) with image maps in HTML. You might for
example have a map of Germany and then branch out to dynamic views of
the Bundesländer.

> 2. Do not use compressed imagery unless you fully understand how the
> decompression works.
> 3. Do not use compression schemes that require a LOT of data to be read
> from disk in order to decode a small portion of the image.

This is a very important point. You gain nothing from a compression
scheme that has to read the entire file to decode a small section of the
image. This fact can completely destroy your performance, and most of
all: it's a hell to debug. I am emphasizing this because I spent quite
some time with it.

Btw: Hard disks are cheap :)

> 4. Use good disk hardware (RAID-5) and organization.
> 5. Use lots of RAM so the server can both cache data and avoid swapping.

RAM. Give. More. Throw it at me. Now.

5. a) Get someone with a clue about hardware to help you. I was really
amazed how much detailed knowledge about which kind of RAM and hard disk
to use in combination with mainboard X and operation system Y can gain
you in performance.

> 6. Tile the imagery into tiles that are of relatively modest size and
> use tile indexes.  Do not break the tiles too small - most map requests
> should require only one input tile to be read.

6. a) Do not only tile your data, but also make sensible decisions on
when and where to show them. MAXSCALE and MINSCALE are your friends.
Never show everything you've got at once, no matter how great it would
look. The smaller (and fewwer) your chunks are, the less time the
computer has to spend with time-critical data processing.



thorsten