[Tilecache] Re: Concurrent Seeding

[Bill Teluk]

Update:
I've written a Bash script based on Tedman Eng's multiple process script as
published in the "Advanced Bash Scripting Guide" (Mendel Cooper) and I can
get multiple instances of the the seeding program to run, each with an
individual bbox and zoom range.  The script can be reconfigured to vary the
number of processes to execute concurrently.
However, I don't get any signficant improvement when running anything more
than about 3 concurrent.  My CPU is about 83% idle!!! (that's on a 24 CPU
box with 48G of RAM.)  And the resulting speed is about 2.4 times the amount
of time to generate tiles in serial.  In fact, increasing the number of
concurrent processes, eg. to 10 or 20, actually slows down the tile
generation rate slightly.

Is there some sort of common resource that TileCache uses that get's locked
or otherwise acts as a bottleneck when seeding?  Or is there some method by
which I can tweak the system to get it to work faster?

I'm using modPython, an FGS v9.5 MapServer install on a RHEL5.5 Linux,
PostgreSQL v9.0.3, PostGIS 1.5.2, the layer is sourced from Postgres and is
a street directory map based on some 35 odd layers (100 classes) in the Map
file.

Regards, Bill Teluk

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