Clear active connections after initialization #28057
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Any connections that were checked out during initialization should be checked back in before the first request is processed, for two reasons: - Returning the connection to the pool allows it to be health checked before it's used again. If the connection dies before the first request arrives, the health check will replace it with a new one. - If the thread that initialized Rails is not the same thread that will be performing work, checking in the connection will allow it to be reused instead of being stuck to the initialization thread forever.
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Unless told otherwhise, when this proxy class intercepts methods, it will create a connection if one does not already exist. https://github.com/zendesk/active_record_host_pool/blob/v0.11.0/lib/active_record_host_pool/pool_proxy.rb#L107-L108 In Rails 5.2.0, they added the following functionality which caused issues with code mentioned above https://github.com/rails/rails/blob/v5.2.3/activerecord/lib/active_record/railtie.rb#L180-L195 Here's the associated PRs rails/rails#28057 rails/rails#31221 This patch overrides the methods, retrieves the connection if it's active and calls super without creating a new one. This resolves an issue for applications upgrading to Rails 5.2.3 whereby connections would be created and thrown away during Rails.application.initialize!
mriddle
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Aug 22, 2019
Unless told otherwhise, when this proxy class intercepts methods, it will create a connection if one does not already exist. https://github.com/zendesk/active_record_host_pool/blob/v0.11.0/lib/active_record_host_pool/pool_proxy.rb#L107-L108 In Rails 5.2.0, they added the following functionality which caused issues with code mentioned above https://github.com/rails/rails/blob/v5.2.3/activerecord/lib/active_record/railtie.rb#L180-L195 Here's the associated PRs rails/rails#28057 rails/rails#31221 This patch overrides the methods, retrieves the connection if it's active and calls super without creating a new one. This resolves an issue for applications upgrading to Rails 5.2.3 whereby connections would be created and thrown away during Rails.application.initialize!
mriddle
added a commit
to zendesk/active_record_host_pool
that referenced
this pull request
Aug 22, 2019
Unless told otherwhise, when this proxy class intercepts methods, it will create a connection if one does not already exist. https://github.com/zendesk/active_record_host_pool/blob/v0.11.0/lib/active_record_host_pool/pool_proxy.rb#L107-L108 In Rails 5.2.0, they added the following functionality which caused issues with code mentioned above https://github.com/rails/rails/blob/v5.2.3/activerecord/lib/active_record/railtie.rb#L180-L195 Here's the associated PRs rails/rails#28057 rails/rails#31221 This patch overrides the methods, retrieves the connection if it's active and calls super without creating a new one. This resolves an issue for applications upgrading to Rails 5.2.3 whereby connections would be created and thrown away during Rails.application.initialize!
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Any connections that were checked out during initialization should be checked back in before the first request is processed, for two reasons:
Returning the connection to the pool allows it to be health checked before it's used again. If the connection dies before the first request arrives, the health check will replace it with a new one.
If the thread that initialized Rails is not the same thread that will be performing work, checking in the connection will allow it to be reused instead of being stuck to the initialization thread forever.
The second use case was the reason I wrote this patch - we run a lot of Sidekiq processes at @intercom, and deploying this reduced the peak open connection count on our database by 13%.