Re: [boost] Is disabling boost log auto flush the only way to control the log flush? Or can you change log auto flush rate?

Subject: Re: [boost] Is disabling boost log auto flush the only way to control the log flush? Or can you change log auto flush rate?
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2018-12-13 10:00:16

On 12/13/18 6:55 AM, hh h via Boost wrote:
> Hi,
> 
> I use boost log in an embedded system where flushing log message to
> flash storage need be controlled. I could not find how to change log
> auto flush rate, is it the only way to disable auto flush
> boost::log::keywords::auto_flush = false? I think there must be a way
> to change a desired log flush rate value without disabling auto flush,
> appreciate any tips.

Auto flush is disabled by default, you don't need to disable it explicitly.

When not enabled, the rate of flushing is system dependent - basically, 
it happens when C/C++ runtime library detects its internal buffer 
overflow when Boost.Log tries to write a new record to the file stream. 
I'm not aware of any ways to influence that, so the flush will happen at 
least that often. Additionally, you can flush the stream buffer manually 
by calling flush() on the logging core or the sink at the points you 
feel appropriate.

However, I should note that flushing the buffer from Boost.Log side does 
not necessarily mean writing the data to the flash media. Normally, the 
flush operation simply invokes the OS write operation, which places the 
data in the filesystem cache to write it later. The OS may combine 
multiple such write operations in the cache before the data is actually 
written to the media. If it is the flash media health that concerns you, 
you should research how you can tune filesystem cache in your OS first, 
before tampering with your application, as this will give the most 
tangible benefit, even beyond writing logs.