feat: Rework tenant cache #1601
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,26 @@ | ||
| package main | ||
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| import ( | ||
| "flag" | ||
| "strings" | ||
| ) | ||
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| type StringList []string | ||
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| var _ flag.Value = (*StringList)(nil) | ||
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| func (l *StringList) String() string { | ||
| if l == nil || len(*l) == 0 { | ||
| return "" | ||
| } | ||
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| return strings.Join(*l, ", ") | ||
| } | ||
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| func (l *StringList) Set(value string) error { | ||
| for v := range strings.SplitSeq(value, ",") { | ||
| *l = append(*l, strings.TrimSpace(v)) | ||
| } | ||
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| return nil | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,49 @@ | ||
| package main | ||
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| import ( | ||
| "testing" | ||
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| "github.com/stretchr/testify/require" | ||
| ) | ||
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| func TestStringList(t *testing.T) { | ||
| { | ||
| var sl StringList | ||
| require.Equal(t, "", sl.String()) | ||
| } | ||
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| { | ||
| var sl StringList | ||
| require.NoError(t, sl.Set("a")) | ||
| require.Equal(t, []string{"a"}, []string(sl)) | ||
| require.Equal(t, "a", sl.String()) | ||
| } | ||
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| { | ||
| var sl StringList | ||
| require.NoError(t, sl.Set("a,b")) | ||
| require.Equal(t, []string{"a", "b"}, []string(sl)) | ||
| require.Equal(t, "a, b", sl.String()) | ||
| } | ||
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| { | ||
| var sl StringList | ||
| require.NoError(t, sl.Set("a,b,c")) | ||
| require.Equal(t, []string{"a", "b", "c"}, []string(sl)) | ||
| require.Equal(t, "a, b, c", sl.String()) | ||
| } | ||
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| { | ||
| var sl StringList | ||
| require.NoError(t, sl.Set("a, b")) | ||
| require.Equal(t, []string{"a", "b"}, []string(sl)) | ||
| require.Equal(t, "a, b", sl.String()) | ||
| } | ||
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| { | ||
| var sl StringList | ||
| require.NoError(t, sl.Set(" a, b ")) | ||
| require.Equal(t, []string{"a", "b"}, []string(sl)) | ||
| require.Equal(t, "a, b", sl.String()) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,106 @@ | ||
| // Package cache provides an interface-based caching system with multiple implementations. | ||
| // | ||
| // The package defines a Cache interface that all implementations must satisfy, | ||
| // allowing the agent to use different cache backends interchangeably. This design | ||
| // eliminates the need for nil checks throughout the codebase. | ||
| // | ||
| // Available implementations: | ||
| // - Memcached: Distributed cache using memcached servers | ||
| // - Noop: No-op cache for testing and fallback (always returns ErrCacheMiss) | ||
| // | ||
| // The cache supports multiple memcached servers, custom expiration times, | ||
| // and automatic serialization/deserialization of Go values using encoding/gob. | ||
| // | ||
| // Example usage with memcached: | ||
| // | ||
| // cc, err := cache.New(cache.Config{ | ||
| // Servers: []string{"localhost:11211", "cache1:11211"}, | ||
| // Logger: logger, | ||
| // }) | ||
| // if err != nil { | ||
| // // Fall back to noop cache | ||
| // cc = cache.NewNoop(logger) | ||
| // } | ||
| // | ||
| // // Store a struct | ||
| // err = cc.Set(ctx, "user:123", user, 5*time.Minute) | ||
| // | ||
| // // Retrieve a struct | ||
| // var user User | ||
| // err = cc.Get(ctx, "user:123", &user) | ||
| // if err == cache.ErrCacheMiss { | ||
| // // Key not found, fetch from source | ||
| // } else if err != nil { | ||
| // // Other error (network, deserialization, etc.) | ||
| // log.Warn("cache error: %v", err) | ||
| // } | ||
| // | ||
| // Example usage with noop cache (for testing): | ||
| // | ||
| // cc := cache.NewNoop(logger) | ||
| // // All Get operations return ErrCacheMiss | ||
| // // All Set/Delete/Flush operations succeed but do nothing | ||
| package cache | ||
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| import ( | ||
| "context" | ||
| "flag" | ||
| "time" | ||
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| "github.com/grafana/synthetic-monitoring-agent/internal/error_types" | ||
| ) | ||
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| const ( | ||
| // ErrCacheMiss is returned when a key is not found in the cache. | ||
| // This is a sentinel error that allows callers to distinguish between | ||
| // a cache miss and other errors (network issues, serialization failures, etc.). | ||
| ErrCacheMiss = error_types.BasicError("cache miss") | ||
| ) | ||
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| // Cache defines the interface for cache operations. | ||
| // All cache implementations (memcached, noop, local, etc.) must implement this interface. | ||
| // | ||
| // 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 { | ||
| // 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 | ||
|
Contributor
Author
There was a problem hiding this comment. 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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| // Get retrieves a value from the cache and deserializes it into dest. | ||
| // Returns ErrCacheMiss if the key is not found. | ||
| // Returns an error for other failures (network, serialization, etc.). | ||
| Get(ctx context.Context, key string, dest any) error | ||
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| // Delete removes a key from the cache. | ||
| // Returns nil if the key doesn't exist (idempotent). | ||
| Delete(ctx context.Context, key string) error | ||
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| // Flush removes all items from the cache. | ||
| // Use this operation cautiously as it affects all cache users. | ||
| Flush(ctx context.Context) error | ||
| } | ||
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| type Kind string | ||
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| var _ flag.Value = (*Kind)(nil) | ||
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| const KindAuto Kind = "auto" | ||
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| const ErrUnsupportedCacheKind = error_types.BasicError("unsupported cache type") | ||
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| func (val *Kind) Set(s string) error { | ||
| switch s { | ||
| case string(KindAuto), string(KindLocal), string(KindMemcached), string(KindNoop): | ||
| *val = Kind(s) | ||
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| return nil | ||
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| default: | ||
| return ErrUnsupportedCacheKind | ||
| } | ||
| } | ||
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| func (val Kind) String() string { | ||
| return string(val) | ||
| } | ||
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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.
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Yeah, I think I initially expected a multi-tiered implementation. It's not something we need to implement immediately, I'm fine with running this using one or the other first and getting some data out of it.
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The idea is to run with Otter by default and test with memcached in a couple of places.