On Monday, November 6, 2017 at 12:18:13 PM UTC+1, [email protected] wrote:
>
> Hi everyone,
> I'm currently trying to use the connection_validator extension in a way
> that it validates the connections on every checkout. While I was reading
> the docs about this extension, I stumbled on this:
>
> Note that if you set the timeout to validate connections on every
>> checkout, you should probably manually control connection checkouts on a
>> coarse basis, using Database#synchronize. In a web application, the optimal
>> place for that would be a rack middleware.
>
>
> I could not understand exactly what "manually control the connection
> checkouts on a coarse basis" is supposed to mean. Maybe someone here can
> help me understand this operation, and why it helps to prevent performance
> issues on this case?
>
If you don't do this, and you set the validation timeout to -1, every time
you checkout a connection, it will run a query to see if the connection is
still active. Even some simple things like correctly escaping string
literals can require connection checkouts, which can result in a major
slowdown.
A coarse checkout would be:
DB.synchronize do
# your code here
end
In terms of a rack middleware, something like:
class CoarseCheckout
def initialize(app, db)
@app = app
@db = db
end
def call(env)
db.synchronize{@app.call(env)}
end
end
use CoarseCheckout, DB
Hopefully that answers your question. If you have more questions, please
ask.
Thanks,
Jeremy
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