Is disabling boost log auto flush the only way to control the log flush? Or can you change log auto flush rate?
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. Thank you. JHH
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.
Thanks Andrey.
I am using OpenWrt, it seems to me that OS filesystem does not have
mechanism to handle write data in two stages, so I have to use manual
flush I am currently implementing which works well anyway.
Thank you very much.
JHH
On 12/13/18, Andrey Semashev via Boost
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.
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