Rails - Jun 2013 - Changing log level at runtime in a multithread server like unicorn

How can I change the log-level at runtime *without restarting* or creating 
new forks?

I was thinking of having a controller that - with proper authentication- 
allows a user to set the log level of a specific server, i.e. the server 
the controller resides on. 
Because we are in a threaded environment changing the log level of one 
thread would not affect the others (correct me if I am wrong) so I was 
thinking I write the new log level to a file.
To not waste time reading the file on each log request I was thinking about 
setting a "global" persistent-across-requests variable that has the
time of
the last check and if more than 10s elapsed it reads the file again and 
sets the log level to the value in the file, if this is a valid one.

The usecase is that let''s say 20 servers are running and an API call
may
return corrupted data or has a huge performance spike. So now I want to 
turn on a logging level that shows me i.e. the queries that were executed, 
and if that does not help, show even more data that is saved on
"debug"
level.  When there are no problems I want to restrict the logging to 
"error" so no unnecessary logging takes place and wastes cpu/space.

Any thoughts on this method or if there is a better one?


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On Tuesday, June 11, 2013 4:35:28 AM UTC+1, Markus
wrote:
>
> How can I change the log-level at runtime *without restarting* or 
> creating new forks?
>
> I was thinking of having a controller that - with proper authentication- 
> allows a user to set the log level of a specific server, i.e. the server 
> the controller resides on. 
> Because we are in a threaded environment changing the log level of one 
> thread would not affect the others (correct me if I am wrong) so I was 
> thinking I write the new log level to a file.
> To not waste time reading the file on each log request I was thinking 
> about setting a "global" persistent-across-requests variable that
has the
> time of the last check and if more than 10s elapsed it reads the file again
> and sets the log level to the value in the file, if this is a valid one.
>
> The usecase is that let''s say 20 servers are running and an API
call may
> return corrupted data or has a huge performance spike. So now I want to 
> turn on a logging level that shows me i.e. the queries that were executed, 
> and if that does not help, show even more data that is saved on
"debug"
> level.  When there are no problems I want to restrict the logging to 
> "error" so no unnecessary logging takes place and wastes
cpu/space.
>
>
Changing it per server seems fiddly - how do you ensure that the request is 
handled by the server you expect it to ? I think the log level is a per 
process thing, but you have multiple processes so the problem remains. A 
file you can touch seems reasonable - Passenger etc. do something similar 
for monitoring changes to the tmp/restart.txt so it''s probably a viable
mechanism.

Fred 

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