schema_load triggers 2nd schema_load (via locking) #24653

kbrock · 2016-04-20T15:30:30Z

Summary

Rails is double loading (schema_load!) for all of our models.

Details

Currently, loading the schema (schema_load)
accesses the locking column (locking_column)
which defaults the value (reset_locking_column)
which invalidates the schema (reload_schema_from_cache)
which forces another schema load (schema_load).

Good news:

The second schema_load does accesses locking_column,
but locking_column is set this time through, so it does not call reset_locking_column
and it does not trigger an infinite loop.

Solution

I feel reset_locking_column should still invalidate the schema.
So instead, this sets @locking_column directly in the default case only.
Please let me know if you have another solution.

/cc @matthewd

rails-bot · 2016-04-20T15:31:08Z

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @matthewd (or someone else) soon.

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rafaelfranca · 2016-04-20T17:01:51Z

activerecord/lib/active_record/locking/optimistic.rb

@@ -150,7 +150,7 @@ def locking_column=(value)

        # The version column used for optimistic locking. Defaults to +lock_version+.
        def locking_column
-          reset_locking_column unless defined?(@locking_column)
+          @locking_column = DEFAULT_LOCKING_COLUMN unless defined?(@locking_column)


Do you know why reset_locking_column invalidated the schema?

@rafaelfranca I am not sure if you asked do I know why that is wanted, or literally how is that done.

locking_column calls reset_locking_column

reset_locking_column calls locking_column=

locking_column= calls reload_schema_from_cache

I'm looking into writing tests for this. but they are a little tricky

@rafaelfranca looked through history of this file (didn't branch out to other files) and even wondering if locking_column= or reset_locking_column even needs to reload the schema.

Oh, that was the information I was looking, thanks.

If table_name= reload the schema so they should.

kbrock · 2016-04-21T03:43:49Z

added tests. Here are the numbers from before this PR and after.

test	# loads before	# loads after
`test_basic_model_is_loaded_once`	2	1
`test_model_with_custom_lock_is_loaded_once`	1	1
`test_model_with_changed_custom_lock_is_loaded_twice`	3	2

I had expected basic_model and model_with_custom_lock to behave similarily. The first one just uses the default.
I expected model_with_changed_custom_lock to load a second time. (the 3 value makes sense there, but really should be 2)

kbrock · 2016-04-21T14:41:15Z

rebased to kick build. (jruby timeout looked bogus) (I didn't squash, but can if you want that)

Currently, loading the schema (schema_load) accesses the locking column (locking_column) which defaults the value (reset_locking_column) which invalidates the schema (reload_schema_from_cache) which forces another schema load. Good news: The second schema_load does accesses locking_column, but locking_column is set, so it does not reset_locking_column and it does not trigger an infinite loop. The solution is not invalidate the cache while default locking_column

kbrock · 2016-04-28T21:49:37Z

kicking again. hope faye build failure is not related

kbrock · 2016-04-28T22:00:37Z

Thanks @rafaelfranca

jeremy · 2016-04-30T01:04:49Z

activerecord/test/cases/schema_loading_test.rb

@@ -0,0 +1,53 @@
+require 'thread'


@kbrock How are we relying on this here? See #24790

Thank you @jeremy - very good eye. I found a solution that no longer needed the thread but it got left in.

Thank you but all kudos to @vipulnsward's sharp eye 😊

rails-bot assigned matthewd Apr 20, 2016

rafaelfranca reviewed Apr 20, 2016
View reviewed changes

maclover7 added the activerecord label Apr 20, 2016

kbrock force-pushed the kinder_locking_column branch from 023d2d5 to 2b5faec Compare April 21, 2016 14:40

kbrock added 2 commits April 28, 2016 17:48

test the number of times the schema is loading

ba05b3c

kbrock force-pushed the kinder_locking_column branch from 2b5faec to ba05b3c Compare April 28, 2016 21:48

rafaelfranca merged commit 03b62b8 into rails:master Apr 28, 2016

kbrock deleted the kinder_locking_column branch April 28, 2016 22:00

jeremy reviewed Apr 30, 2016
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schema_load triggers 2nd schema_load (via locking) #24653

schema_load triggers 2nd schema_load (via locking) #24653

kbrock commented Apr 20, 2016 •

edited

rails-bot commented Apr 20, 2016

rafaelfranca Apr 20, 2016

kbrock Apr 20, 2016

kbrock Apr 20, 2016 •

edited

rafaelfranca Apr 20, 2016

rafaelfranca Apr 20, 2016

kbrock commented Apr 21, 2016 •

edited

kbrock commented Apr 21, 2016 •

edited

kbrock commented Apr 28, 2016

kbrock commented Apr 28, 2016

jeremy Apr 30, 2016

kbrock Apr 30, 2016

jeremy Apr 30, 2016

schema_load triggers 2nd schema_load (via locking) #24653

schema_load triggers 2nd schema_load (via locking) #24653

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kbrock commented Apr 20, 2016 • edited

Summary

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Solution

rails-bot commented Apr 20, 2016

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kbrock commented Apr 20, 2016 •

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kbrock commented Apr 21, 2016 •

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kbrock commented Apr 21, 2016 •

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