FileTarget - RetryingMultiProcessFileAppender should use BufferSize=1024

[snakefoot]

Logger Name	Messages	Size	Threads	Loggers
PerfSyncLogger	10.000	16	1	1

BufferSize	Time (ms)	Msgs/sec	GC2	GC1	GC0	CPU (ms)	Mem (MB)
32768	26.918	371	0	1	22	3.312	36,332
4096	26.745	373	0	0	3	3.203	35,680
1024	26.433	378	0	0	1	3.093	35,496

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This change is 

[codecov-io]

Current coverage is 82% (diff: 100%)

Merging #1864 into master will decrease coverage by <1%

@@             master      #1864   diff @@
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  Files           276        276          
  Lines         18472      18471     -1   
  Methods        2857       2856     -1   
  Messages          0          0          
  Branches       2129       2130     +1   
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- Hits          15061      15055     -6   
- Misses         2922       2928     +6   
+ Partials        489        488     -1   

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[304NotModified]

Less then 2% improvement. Not sure if this benefit is large enough. What do you think?

Reason not the merge:

• possible slower in other configurations
• buffersize is "dynamic", more difficult to document

[snakefoot]

Tried some testing with the FileTarget within the AsyncWrapper, and the improvement was also small there. Will close this.

[snakefoot]

@tlaguz Regarding " Unhandled exception when writing to file". Consider changing your NLog-File-Target to use keepFileOpen="true" or specify bufferSize="1024". This will avoid the allocation of 30 KByte buffer for every log-event-write-operation (No longer needed with #3444 with NLog 4.6.5)

[snakefoot]

Superseeded by #3444