McIDAS-XCD Administrator's Guide
Version 2011.1
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Deletes real-time grid or MD files.
QRTMDG GRID bfile
efile numdays
QRTMDG MD bfile efile numdays
The QRTMDG command is used to maintain the "cylinders" of real-time MD and grid files. The cylinders are groups of ten files whose file number is based on the last digit of the Julian date. For example, data from day 135 are stored in files 5, 15, 25, etc., and data from day 310 are stored in files 10, 20, 30, etc. Since each cylinder consists of ten files you can keep up to nine days of data online. QRTMDG is used to delete all but the numdays most recent files in each cylinder. For example, if you run QRTMDG with a value of 4 in numdays on day 135, the real-time files for days 135, 134, 133 and 132 are retained.
SSEC recommends scheduling QRTMDG to run at 00:01 UTC daily to delete the old MD and grid files from your real-time cylinders.
QRTMDG works during the transition to a new year by determining the Julian date of the next day and deleting the files for that day. For example, running QRTMDG on day 002 will delete files 3, 13, 23,... (which contained day 363 data) so they can be written when data for day 003 arrives.
Due to the cylinder structure and day numbering during the transition to a new year (from days ...,364, 365 to 001, 002,...) there are limits to the number of days of data you can keep online between days 365 and 008 because, for example, MD file 4 can store data for day 364 or 004, but not both. During a non-leap year transition (e.g., 2005-2006), the constraints limit you to a maximum of four files on day 004; five files on days 003 and 005; six files on days 002 and 006; seven files on days 001 and 007; and eight files on days 365 and 008. During a leap year transition (e.g., 2008-2009), the constraints limit you to five files on days 003, 004 and 005; six files on days 002 and 006; seven files on days 001 and 007; and eight files on days 366 and 008.
If you store four or less days of data (five or less days during leap year transitions), QRTMDG works as expected because there are no day numbering conflicts. For example, running QRTMDG each day with a numdays value of 4 retains surface hourly MD files 5, 4, 3, 2 on day 365; files 1, 5, 4, 3 on day 001; files 2, 1, 5, 4 on day 003, etc.
SKE 2006129 00:01:00 999999 24 "QRTMDG MD 1 40 4
This example stores the current day's MD data plus the previous three days for MD files in the range 1 to 40. When this command runs on day 2006307, all MD files in the range 1 to 40 are deleted except: 4, 5, 6, 7, 14, 15, 16, 17, 24, 25, 26, 27, 34, 35, 36 and 37.
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