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Archive Compression Example: Archive Compression of Straight Line

In this case we have a straight flat line. Assume a small archive compression deadband, say 2% on a 0 to 100 EGU span. Since data occurs on a straight flat line, the deadband will never be exceeded.


Time	Value	Quality
t0	2	Good
t0+5	2	Bad
t0+10	2	Good
t0+15	2	Good
t0+20	2	Good

Shut down and restart the archiver, then perform the following SQL query:

select * from ihRawData where samplingmode=rawbytime and tagname = t20.ai-1.f_cv and timestamp > today

Only t0 and t0+20 were stored. T0 is the first point and T0+20 is the held sample written to disk on archiver shutdown, even though no deadband was exceeded.