Archiver queried for values even if ncount=0

[georgweiss]

In ApplianceArchiverReader L140 the archiver(s) are queried for the number of data points calling getNumberOfPoints which - no points are found - will call getNumberOfPointsLegacy.

Now if this chain of calls returns zero, then the archiver is called to retrieve raw values anyway.

So I have some questions:

1. When is getNumberOfPointsLegacy needed? Is this related to certain versions of the archiver appliance? If so, then it should be possible to omit the call if only newer versions are used.
2. If the count is zero, should not the call for values be omitted completely?
3. Since retrieving values will contain information on the number of values, why call getNumberOfPoints in the first place?

I'm asking this since we are migrating to a new clusters, but we're not migrating data. So Phoebus needs to query twice as many endpoints for each plot, putting load on both the application and the archiver services. And network.

[kasemir]

When is getNumberOfPointsLegacy needed?

No idea, that's internal to the archive appliance client implementation

If the count is zero, should not the call for values be omitted completely?

Yes, if you know that there are no values, then the call could return an empty value iterator

Since retrieving values will contain information on the number of values, why call getNumberOfPoints in the first place?

The goal here is to decide if we can return the raw data (count is below some threshold "count"), or if we should return "optimized" min/max/average type of data because there are way too many rows of raw data.

[georgweiss]

Sure, but ncount=0 should indicate that there's no point getting raw data at all. Right?

I'm asking this since we have added new archiver clusters and now have a total of 4. Which means each plot will make the data browser send off a lot of requests. In view of how we organize these clusters over time only one of them will have the wanted data.

[kasemir]

Yes, if you know that there are no values, then the call could return an empty value iterator