Data Taking

1. Data Taking Bob Dalesio Sept. 4, 1997

2. 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

3. Data Taking Events • Channel • Periodically* • On Change • Set • On Demand* • Periodically • On Change

4. 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

5. 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

6. 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

7. Buffering and Disk Organization - set data Header set0 set1 set2 Ca_get set Next set memory disk

8. Buffering and Disk Organization - channel data Header sample0 sample0 sample1 sample1 sample2 sample2 disk Next Ca_get/ monitor channel0 Next Next memory Memory circ buffer Next Header sample0 sample0 sample1 sample1 sample2 sample2 Ca_get/ monitor channel1 Next Next memory Memory circ buffer Next Next

9. 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

10. 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