[BUG] compatibility with oracle 11c

[MansuyDavid]

Description

when connecting to oracle 11c db we have errors :
level=INFO source=database.go:220 msg="dbtype err" error="dpiStmt_execute: ORA-02003: invalid USERENV parameter\nHelp: https://docs.oracle.com/error-help/db/ora-02003/" database=oracle

Details

I found that this error is caused by database.go:getDBtype.
but i found also that this metric is never exposed when scrapInterval is used. collector.go:RunScheduledScrapes

So about this metric :

1. this metric is not really usefull : remove it
2. this metric must be used only when scrapinterval is not set (but this seems really strange to me) : so do not execute this request if scrapinterval is used. (no need to execute it if not exposed).
3. this metric must be used no matter scrapinterval :
   a- add this metric to the exposed metrics for RunScheduledScrapes.
   b- change the handling of this request to have for example "-1" as value if an error occured. (this is the way we are doing internnaly for now)

I know that 11c is not maintained by oracle, but this metric is the only thing that make this exporter not compatible with 11c.

[markxnelson]

Hi @MansuyDavid - that's just an INFO message - does it actually prevent the exporter from working, or is it just noise in the log?

[MansuyDavid]

You are right, this is only logging issue in my case (i use scrapinterval, so this request is done only at "connect" or "ping" if i understand well, so one log each 60s)

[anders-swanson]

I do like the suggestion of moving this to a metric, which could live in the default metrics file. This gives users the benefit of configuring/disabling this metric as needed.

[markxnelson]

fyi, we do use this metric in other products to descriminate between a CDB, PDB and a pre-mulittenant DB.