[WIP] Load schema caches for all connections #34449
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Do you mean this doesn't work in master for the same reasons? Or that this new code doesn't work? |
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@eileencodes Sorry, I'll clarify: TL;DR I mean this doesn't work on master for the same reasons. Once we find a fix for the fixtures PR problem, this PR should work. The schema cache initializer works if you apply this fix outlined in the fixtures PR. The fix seems to break other things like how we run migrations for each database in |
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This PR proposes moving the schema cache from the connection to the pool so the connection can ask the pool for the cache. In a future PR our goal is to be able to read the yaml file from the pool so we can get rid of the `active_record.check_schema_cache_dump` initializer. This will fix the issues surrounding dumping the schema cache and mulitple databases. Why do we want to get rid of the initializer you ask? Well I was looking at rails#34449 and trying to make it work for our usecase and it revealed A LOT of problems. There are a few issues that I will fix in remaining PRs with SchemaMigration, but there's a big glaring issue with this initializer. When you have an application with multiple databases we'll need to loop through all the configurations and set the schema cache on those connections. The problem is on initialization we only have one connection - the one for Ar::Base. This is fine in a single db application but not fine in multi-db. If we follow the pattern in rails#34449 and establish a connection to those other dbs we will end up setting the cache on the _connection object_ rather than on all connections that connect for that config. So even though we looped through the configs and assigned the cache the cache will not be set (or will be set wrong) once the app is booted because the connection objects after boot are _different_ than the connection objects we assigned the cache to. After trying many different ways to set the schema cache `@tenderlove` and I came to the conclusion that the initializer is problematic, as is setting the schema cache twice. This is part 1 to move the cache to the pool so the cache can read from the schema cache yaml file instead of setting it when initializing the app. To do this we have created a `NullPool` that initializes an empty cache. I put the `get_schema_cache` and `set_schema_cache` in an `AbstractPool` so we can share code between `ConnectionPool` and `NullPool` instead of duplicating code. Now we only need to set the schema_cache on the pool rather than the connection. In `discard!` we need to unset the connection from the schema_cache - we still want the cache just not the connection.
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This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. |
This was referenced Jan 29, 2020
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Summary
Loads schema caches for each connection. This currently doesn't work for the same reasons as the multi-db fixtures PR (#33945).