Retry exporting unsuccessfully exported batches

[bencehornak]

Current behavior

Since #1326 when the SDK exports batches from the disk it essentially ignores any exporting failures and deletes the unsuccessfully exported batches from the disk. Consequently, valuable telemetry might be dropped silently, if there is any exception taking place in the OTel exporter (e.g. IOException due to the device being offline or the backend experiencing a temporary outage).

Proposed behavior

The export scheduler stops exporting on the first failure to prevent the deletion of unconsumed signals. On the next periodic run, the exporting will be retried from the point where the previous attempt left off.

Note

I think the root cause of the problem is the wrong example in the disk buffering module's README, see open-telemetry/opentelemetry-java-contrib#2539.

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.39%. Comparing base (73b6d7f) to head (fed62e0).

Files with missing lines	Patch %	Lines
.../diskbuffering/scheduler/DefaultExportScheduler.kt	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1493      +/-   ##
==========================================
- Coverage   63.51%   63.39%   -0.13%     
==========================================
  Files         159      159              
  Lines        3152     3144       -8     
  Branches      326      325       -1     
==========================================
- Hits         2002     1993       -9     
- Misses       1050     1051       +1     
  Partials      100      100              

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