Thanks John. Among the groups we collaborate with there are some folks
that are quite concerned about the scaling issue. Personally, my direct
experience at this point that indicates that the performance is just
fine (at least so far) even with our largest catalogs.
What's the experience of the list? Are folks seeing unacceptable TDS
initialization because of time spend reading catalogs? The thread from
John Maurer about aggregation access issues notwithstanding.
Roland
On 01/03/2011 07:34 PM, John Caron wrote:
On 1/3/2011 10:53 AM, Roland Schweitzer wrote:
Hi,
We're starting to put together some "big" server-side configuration
catalogs (both with "lots" of dataset elements and "lots" of
catalogRef elements). We are wondering about the process TDS goes
through to read the catalog when is starts. What gets cached? Does
it have a way to know a referenced catalog is unchanged? When do
referenced catalogs get scanned? And so on.
Is there some documentation or a flow chart on how TDS initializes
itself?
Thanks,
Roland
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Hi Roland:
The sad answer is theres not much documentation. Weve been on the
verge of redoing the initialization sequence for a few years now, so
weve been waiting so we can document the clean, cool refactor instead
of the crufty, lame current one.
Anyway, the TDS reads in all the config catalogs at startup. It caches
all of them, and uses the "expires" attribute on the catalog to decide
if/when it needs to reread a catalog. It needs to read all catalogs,
including catalogRef, because it has to know what the possible dataset
URLs are, and there is no contract that a client has to read a catalog
first.
Obviously this doesnt scale forever. Ethan can probably fill in some
details.
see:
http://www.unidata.ucar.edu/projects/THREDDS/tech/catalog/v1.0.2/InvCatalogSpec.html#catalog
John
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