The Frontier distributed database caching system distributes data from
data sources to many clients around the world.
The name comes from "N Tier" where N is any
number and Tiers are layers of locations of distribution. The protocol is http-based and uses a
architecture which is excellent for caching and scales well. The Frontier
the standard web caching tool squid
to cache the http objects at every site. It is ideal for applications
where there are large numbers of widely distributed clients that read
basically the same data at close to the same time, in much the same way
that popular websites are read by many clients.
Large Hadron Collider (LHC) projects,
the database is located at the CERN Tier 0,
and the Frontier system distributes
data to to all the Tier 1, Tier 2, and Tier 3 sites around the world.
Within each site the Frontier system also distributes the data to
all the worker nodes (typically hundreds or thousands) that need to
read the data.
The Frontier system was developed for the
CDF experiment at
Fermilab and is heavily used there.
Fermilab also adapted Frontier for
the CMS experiment at the LHC at
CERN and it is used to access
"conditions data" (mainly detector calibrations and alignments)
at all its sites worldwide. The ATLAS
experiment at the LHC later also adopted Frontier to distribute
conditions data to all of its sites.
Even though this web site is
hosted at CERN for convenience of the LHC projects, Frontier is
maintained by Fermilab. The LHC projects choose the level of
abstraction between client and server to be SQL queries, but the
Frontier system is designed with plugins so applications can put
more of the logic on the server side, and that is how CDF uses it.
There is also a plugin that reads from files on the local disk or
other http web servers. The main advantage of using Frontier
instead of directly using a http web server and squid proxy is
that years of experience have resulted in Frontier supplying
many features that are important for robust and flexible operation
on computing grids. A summary of the features and components of
the Frontier system is available in
this overview webpage.