logging: log maximum concurrency level when talking to backend storage

[jkowalski]

Trying to understand if we're doing something wrong for #1560

[codecov]

Codecov Report

Merging #1629 (8c354a8) into master (13ed6bb) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1629      +/-   ##
==========================================
+ Coverage   70.12%   70.23%   +0.11%     
==========================================
  Files         381      381              
  Lines       30215    30240      +25     
==========================================
+ Hits        21187    21238      +51     
+ Misses       7388     7370      -18     
+ Partials     1640     1632       -8     

Impacted Files	Coverage Δ
repo/blob/logging/logging_storage.go	100.00% <100.00%> (ø)
repo/content/content_manager.go	84.76% <0.00%> (-0.58%)	⬇️
internal/epoch/epoch_manager.go	90.60% <0.00%> (+0.52%)	⬆️
internal/server/server.go	67.94% <0.00%> (+0.64%)	⬆️
repo/maintenance/maintenance_run.go	75.94% <0.00%> (+0.86%)	⬆️
repo/object/object_reader.go	78.53% <0.00%> (+1.46%)	⬆️
repo/content/content_manager_lock_free.go	73.88% <0.00%> (+2.23%)	⬆️
repo/maintenance/maintenance_schedule.go	74.13% <0.00%> (+2.58%)	⬆️
internal/ownwrites/ownwrites.go	81.48% <0.00%> (+2.77%)	⬆️
internal/listcache/listcache.go	83.33% <0.00%> (+3.92%)	⬆️
... and 1 more

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[julio-lopez]

@jkowalski PTAL

[julio-lopez]

minor:

Is there a small race here?

Suppose:

• the state is concurrency == maxConcurrency, for example 7;
• there are two routines g1 and g2 concurrently running beginConcurrency;
• g1 gets v == 8 and g2 gets v == 9;
• both g1 and g2 get mv == 7 and both attempt to update maxConcurrency;
• g1's update succeeds and now maxConcurrency == 8, but concurrency > maxConcurrency

This may self correct if there is a higher concurrency value down the road.