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This pull request introduces a short-TTL (5-minute) cache and request deduplication using singleflight.Group for Looker's LookmlModelExplore API calls, updating several Looker tools to utilize this cached method. Feedback on the changes highlights a potential memory leak due to the cache growing indefinitely without eviction, and a risk of cache corruption or data races because returning the SDK struct by value only performs a shallow copy of nested pointers and slices.
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Description
Each Looker metadata tool (
get_explore,get_dimensions,get_measures,get_filters,get_parameters) issues its ownLookmlModelExploreAPI call for the same(model_name, explore_name)pair. An agent discovery loop inspecting N explores therefore burns ~5 API calls per explore of redundant traffic — significant against Looker's finite per-edition monthly API quotas (e.g. 1,000 admin calls/month on Google Cloud core Standard).This PR adds a short-TTL (5 min) cache for
LookmlModelExploreresponses on the LookerSource, deduplicated withsingleflight, following the same pattern as the existingSource.GetHostURLcache. The five tools now route throughSource.GetLookmlModelExplore.Cache key:
model + explore + fields + add_drills_metadata + sha256(accessToken)[:16]. Keying by caller identity guarantees per-user field-level permissions are never served across users; service-account mode shares one identity, which is correct. Errors are never cached. The returned struct is a shallow copy shared across hits — documented on the method as read-only, matching what all five callers already do.The cache is bounded: entries are purged on write once the map reaches
exploreCacheMaxEntries(512), so long-running servers don't accumulate stale keys (e.g. rotated access tokens or many users).Expected effect: 5 metadata calls per explore collapse to 1 per TTL window; concurrent fan-out collapses to a single upstream request.
PR Checklist
TestGetLookmlModelExploreCachecovers hit, identity-miss, and concurrent singleflight paths)Issue Reference
Fixes #4225