On Friday, February 1, 2013 11:59:09 AM UTC-8, Alex Vinnik wrote:
>
> Hi all.
>
> Looks like we run into an issue with postgres adapter
> when connection_validator extension is used. The problem is simple. DB
> connection is NOT lazy anymore when connection_validator is activated.
> Sequel version is 3.43.0. Consider this snippet
>
> #!/usr/bin/env ruby
>
> require "sequel"
> require 'logging'
>
> logger = Logging.logger(STDOUT)
> logger.level = :debug
>
> logger.info 'Starting...'
>
> DB = Sequel.connect(:adapter => 'postgres',
> :username => 'whatever', :password => 'whatever'',
> :database => 'whatever'', :host => 'localhost')
>
> logger.info DB.inspect
> DB.loggers << logger
>
> DB.extension(:connection_validator)
>
> DB.loggers << logger
> puts `sudo netstat -ntp | egrep '5432.*ESTABLISHED.*#{Process.pid}'`
>
> You can run it and see that DB connection gets established even no SQL is
> fired by the app. It is certainly not a lazy connection.
>
> I, [2013-02-01T13:45:49.668455 #19887] INFO : Starting...
> I, [2013-02-01T13:45:49.729210 #19887] INFO :
> #<Sequel::Postgres::Database: {:adapter=>"postgres",
> :username=>"transporter", :password=>"2ownTransporter",
> :database=>"transporter", :host=>"localhost"}>
> I, [2013-02-01T13:45:49.757414 #19887] INFO : (0.000299s) SET
> standard_conforming_strings = ON
> I, [2013-02-01T13:45:49.757832 #19887] INFO : (0.000280s) SET
> client_min_messages = 'WARNING'
> I, [2013-02-01T13:45:49.758023 #19887] INFO : (0.000129s) SET DateStyle =
> 'ISO'
> tcp6 0 0 ::1:48713 ::1:5432
> ESTABLISHED 19887/ruby
> I, [2013-02-01T13:45:49.831646 #19887] INFO : Finished...
>
> After some digging in the code and seems like calling server_version in
> select_clause_methods triggers DB connection.
>
> https://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/shared/postgres.rb#L1303
> here is server_version code...
>
> https://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/shared/postgres.rb#L453
>
> Just to compare... connecting to MS SQL does have lazy connection. I
> totally understand rationale behind this code and the need to have PG
> version handy in order to prepare statements but it is sort inconsistent
> with other adapters. May be to document this PG connection_validator
> "feature" because I don't think it easily fixable at the moment. What do
> you think?
>
Your analysis appears to be correct, but could you explain why this is an
issue? The point at which Sequel makes a connection is an implementation
detail, so I'm not sure why we should document it. There are other
database extensions that cause a connection (the pg_hstore extension, for
example), so the connection_validator extension is not alone in this.
The fact that Sequel usually creates connections lazily is itself an
implementation detail. It's definitely possible that a connection attempt
will automatically be made on Sequel::Database initialization in the
future, in order to fail fast.
Thanks,
Jeremy
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