[Halld-offline] current best-practice for CCDB access from farm jobs

[Mark Ito]

Folks,

As you know, the guidance on what we should do for accessing CCDB from 
the farm has been a moving target. I won't run down the history for you; 
you're welcome. Let me emphasize: *the following is for the JLab farm*.


      The Recommendation (simple form)

1. Use the latest production version of CCDB: 1.06.07.

2. Set your JANA_CALIB_URL environment variable to 
mysql://ccdb_user@hallddb-farm.jlab.org/ccdb


      The Same Recommendation (pedagogical form)

1. Use the latest production version of CCDB: 1.06.07. Check your 
CCDB_HOME environment variable to confirm this. This version has the 
new, faster query for accessing the MySQL form of the CCDB. If you are 
not using this version, I can help you get set up with it.

2. Set your JANA_CALIB_URL environment variable to

   mysql://ccdb_user@hallddb-farm.jlab.org/ccdb

This happens automatically with the Build Scripts system. The key line 
in the Build Scripts set-up script is:

   setenv JANA_CALIB_URL `$BUILD_SCRIPTS/calib_url_chooser.sh`

for tcsh, and for bash:

   export JANA_CALIB_URL=`$BUILD_SCRIPTS/calib_url_chooser.sh`

where the BUILD_SCRIPTS environment variable points to

   /group/halld/Software/build_scripts

The script calib_url_chooser.sh senses whether or not you are on the 
farm, and if so follows the current recommendation, i.e., uses the MySQL 
server on hallddb-farm.jlab.org. If you are not on the farm it uses 
hallddb.jlab.org, our default MySQL server.

Note that as the recommendation has changed, so too has the choice made 
by calib_url_chooser.sh. So if you use Build Scripts, you don't have to 
know what the current Recommendation is.

   -- Mark




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