feat: Rework tenant cache #1601
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In order to have more resilience in the face of outages, implement an out-of-process cache using memcached. In order to support the existing mode of operation, add an in-process-cache using Otter. Rework the tenant cache to use this new system. Signed-off-by: Marcelo E. Magallon <marcelo.magallon@grafana.com>
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This is the bit that needs the most attention.
| // | ||
| // This interface allows the agent to use different cache backends interchangeably, | ||
| // including a no-op implementation that eliminates the need for nil checks in client code. | ||
| type Cache interface { |
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There are three implementations of this interface.
A memcached one. This is the one I would like to use eventually.
A local one, based on Otter.
A noop one, which is a fallback in case the other two are not available.
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I did consider a multi-tiered implementation, too, using L1 with Otter and L2 with memcached. I would prefer to get some numbers before going that way.
| type Cache interface { | ||
| // Set stores a value in the cache with the specified expiration time. | ||
| // Returns an error if the operation fails. | ||
| Set(ctx context.Context, key string, value any, expiration time.Duration) error |
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This is the bit where I struggled the most.
Otter uses generics to have a more strongly-typed cache. Since the goal is to use memcached, which does not have a strongly-typed API, I thought about multiple clients, one per type, but it was weird.
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Apologies about the large PR. I did consider breaking it up into multiple steps, but it's hard to see where this is going without the changes in the tenant manager code, and it's hard to make the tenant manager changes without the other code. |
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In order to have more resilience in the face of outages, implement an out-of-process cache using memcached. In order to support the existing mode of operation, add an in-process-cache using Otter. Rework the tenant cache to use this new system.