Document :mem_cache_store $MEMCACHE_SERVERS incompatibility
#764
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`:dalli_store` falls back to `$MEMCACHE_SERVERS` if no addresses are given, whereas (prior to Rails 6.1) `:mem_cache_store` goes straight to `localhost:11211`. This is not immediately obvious, especially to users not providing any custom options, and makes it easy to accidentally effectively disable caching entirely (if `localhost:11211` is not a memcached server). Note that rails/rails#40420 added support for `$MEMCACHE_SERVERS`, and is slated for release as part of Rails 6.1. [ci skip]
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Well, that was fast. rails/rails#40420 has been merged already, and should be included as part of the Rails 6.1 release. I've updated the docs accordingly. |
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@petergoldstein what do you think of this change? |
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Maybe I should have pinged @mperham instead? |
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It’s never something Dalli has documented and was a legacy compat thing
from the previous memcache gem.
…On Thu, Oct 29, 2020 at 07:52 Sam Bostock ***@***.***> wrote:
Maybe I should have pinged @mperham <https://github.com/mperham> instead?
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Thanks for the context @mperham. While the behaviour isn't documented in My concern is that making this change can break things without warning -config.cache_store = :dalli_store
+config.cache_store = :mem_cache_storeI was hoping to prevent others from encountering the same issue by calling it out in the migration guide. |
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This adds a warning to
History.mdand3.0-Upgrade.mdto help prevent mistakes when migrating from:dalli_storeto:mem_cache_store.:dalli_storefalls back to$MEMCACHE_SERVERSif no addresses are given, whereas:mem_cache_storegoes straight tolocalhost:11211.This is not immediately obvious, especially to users not providing any custom options, and makes it easy to accidentally effectively disable caching entirely (if
localhost:11211is not a memcached server).Note that rails/rails#40420 would add support for
$MEMCACHE_SERVERS. Nonetheless, I think it would make sense to get this documentation out ASAP to prevent accidents. If the PR is accepted, it would make sense to follow up with a message mentioning specific Rails versions, once it has made it into a release.