data taking
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Data Taking
Bob Dalesio
Sept. 4, 1997
Data Taking Approaches
• Channel -– data buffers contain many samples over different time stamps for the same channel
– saving data requires seeking to the appropriate buffer and emptying the local buffer
– optimized for retrieving data for a few channels over a long time
– memory buffers are used to minimize the disks access during saving
• Set -– data buffers contain many channels for a given time
– saving data only requires one seek for the entire set
– optimized for retrieving a set of data at a given time
Data Taking Events
• Channel – Periodically*
– On Change
• Set
– On Demand*
– Periodically
– On Change
Data Taking - Channel
• Archive Time Stamped Data
• Maximum Rate of 10K samples per second
• Ability to run on multiple platforms
• Positive feedback of data taking
• Maximum save rate of 20 Hz
• Data available for analysis during archiving
Archiving Methods
• Frequency based - data is saved at a predefined frequency– we use monitors for frequencies that are less than every 2 second
– slower channels are fetched using “ca_get”
• Monitor based - data is saved on change– typically the ADEL field determines a significant change
– an ADEL of 0 records every change
– an ADEL of -1 records every time the record is scanned
• Demand - data is saved on a request from the operator
• Trigger - data is saved when some other channel changes
Data Taking - Set
• Save sets periodically, on demand, on change
• Make sets available for hot reboot files
• Make sets available for setpoint restore files
• Capable of 5,000 signals per set
• Positive feedback during operation
• Provide time synchronous sets
Buffering and Disk Organization - set data
setCa_get
set0
set1
set2
Next set
Header
diskmemory
Buffering and Disk Organization - channel data
channel0Ca_get/monitor
sample0
sample1
sample2
Next
Memorycirc buffer
memory
channel1Ca_get/monitor
sample0
sample1
sample2
Next
Memorycirc buffer
memory
sample0
sample1
sample2
Next
Next
Next
Header
sample0
sample1
sample2
Next
Next
Next
disk
Header
Data Retrieval - Channel Data
• Retrieve single channel from time A to time B
• Fetch up to 1024 samples for 1 channel from last 24 hours in under 200 msec
• Fetch up to 1024 samples for 1 channel within the current month in under 1 sec
• Return data as it is being archived
• Return high, low, and number of samples within a time range
• List the channels in the archive file
• Return specified number of samples with statistical information for a specified time period
• Return a set of channels for a single time - not optimized - see set archive
• Search for events
Data retrieval - Set Data
• Access up to 2000 channels for up to 24 samples in the last 24 hours in under 2 seconds
• Access up to 2000 channels from a given time in the last month in under 4 seconds
• Produce named restore sets for a set from a given time
• Produce a warm reboot file for a set from a given time - with backups
• Provide single channel through time - with reduced performance - see channel data
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