[webservices] caching in dataselect and tracedsp

[Bruce Weertman]

John:

Good to hear from you.

A few points about caching:

* Yes ws-dataselect and ws-tracedsp do cache the data. 

* The cache is very specific to the request that you make.

If you asked for some time period from some  channel and then asked for exactly the same
time period from the same  channel, you would hit the cache and it should return much faster. 
If the second request's time range was just a fraction of a second different than there first's, you would not
as there would then be two objects in the cache. This is because the 'token' to the cached objects
are generated from  hashes of request parameters. Changing a request in just the slightest
way will generate a completely different hash.

* ws-bulkdataselect does not cache data.

* The underlying NFS filesystem which holds the archive and everything else we do here and the DMC
does some caching of it's own. Going to datasets that are close to each other can result in sped up
requests as a result. Performance may vary depending on many different factors including 
system load and  how close to each other subsequent queries are.


Hope that helps.

Cheers,
-Bruce



On Sep 25, 2012, at 11:17 AM, John D. West wrote:

> Hello.
> 
> I am working on code that retrieves corrected traces from the DMC using the dataselect and tracedsp web services. I notice that a second retrieval of the same data is much, much faster, presumably because the data is being cached by the DMC web services. I am retrieving broadband 40Hz data in 60-hour increments.
> 
> Do these web services cache more data than I ask for? Can I speed up my requests by either sequentially asking for data for the same channel (i.e., ask for 60 hours of BHZ for a station, then ask for the next 60 hours, etc.) or by asking for multiple traces for the same time period (i.e., 60 hours of BHZ, then 60 hours of BHE & BHN for the same station & time span)?
> 
> Thanks!
> 
>      -- John
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