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