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Archive Compression Example: Archive Compression of Good Data

This example demonstrates that the held value is written to disk when the deadband is exceeded.

In this case, we have an upward ramping line. Assume a large archive compression deadband, such as 75% on a 0 to 100 EGU span.


Time	Value	Quality
t0	2	Good
t0+5	10	Good
t0+10	10	Good
t0+15	10	Good
t0+20	99	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

Because of archive compression, the t0+5 and t0+10 values are not stored. The t0+15 value is stored when the t0+20 arrives. The t0+20 value would not be stored until a future sample arrives, no matter how long that takes.