[jira] [Updated] (HBASE-30406) Add cache access notification support to CacheEngine and cache topologies

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-30406?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

ASF GitHub Bot updated HBASE-30406:
-----------------------------------
    Labels: pull-request-available  (was: )

> Add cache access notification support to CacheEngine and cache topologies
> -------------------------------------------------------------------------
>
>                 Key: HBASE-30406
>                 URL: https://issues.apache.org/jira/browse/HBASE-30406
>             Project: HBase
>          Issue Type: New Feature
>          Components: BlockCache
>            Reporter: Vladimir Rodionov
>            Assignee: Vladimir Rodionov
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 4.0.0-alpha-1
>
>
> h2. Description
> {{CacheEngine}} currently provides {{getBlock()}} for retrieving cached blocks, but there is no lightweight mechanism to notify a cache engine that a block has been accessed without retrieving the block from that engine.
> This is required for cache topologies where the same block may reside in multiple tiers.
> In particular, {{TieredInclusiveTopology}} keeps a block in both L1 and L2. When a request is satisfied from L1, L2 does not observe the access. As a result, the L2 cache engine cannot update access-based eviction, recency, frequency, or admission metadata for the block.
> Add a {{touch(BlockCacheKey)}} operation to {{CacheEngine}}. The operation provides an access notification without retrieving the cached object and without affecting normal cache hit/miss accounting.
> Access propagation should be topology-specific. {{CacheTopology}} should provide a hook for handling successful cache accesses. {{TopologyBackedCacheAccessService}} should notify the topology when a block is found, allowing the topology to propagate the access to other tiers when required.
> For {{TieredInclusiveTopology}}, an L1 hit should result in a {{touch()}} notification to L2. No cross-tier touch is required for {{TieredExclusiveTopology}} or {{SingleTierTopology}}.
> h2. Proposed Changes
> * Add {{CacheEngine.touch(BlockCacheKey)}} with a default no-op implementation.
> * Add a topology-level access notification hook, e.g. {{CacheTopology.handleAccess(...)}}.
> * Update {{TopologyBackedCacheAccessService}} to notify the topology after a successful cache lookup.
> * Update {{TieredInclusiveTopology}} to propagate an L1 hit to L2 using {{touch()}}.
> * Implement {{touch()}} for cache engines that maintain access-based metadata.
> * Add tests for inclusive, exclusive, and single-tier topology behavior.
> h2. Semantics
> * {{touch()}} is a lightweight access notification and does not retrieve the cached object.
> * {{touch()}} is best-effort. If the block is no longer present in the target engine, the operation has no effect.
> * {{touch()}} must not increment normal cache hit/miss statistics.
> * An L1 hit in {{TieredInclusiveTopology}} causes L2 to receive {{touch()}}.
> * An L2 hit does not require an additional {{touch()}} because L2 already observes the access through {{getBlock()}}.
> * {{TieredExclusiveTopology}} does not propagate L1 hits to L2 because the block is not expected to be present in both tiers.
> * {{SingleTierTopology}} requires no additional access propagation.
> * Cache engines that do not need access notifications retain the default no-op behavior.
> h2. Acceptance Criteria
> * {{CacheEngine}} exposes a {{touch(BlockCacheKey)}} operation.
> * L1 hits in {{TieredInclusiveTopology}} are propagated to L2.
> * L2 can update its access metadata without fetching the cached block.
> * {{TieredExclusiveTopology}} and {{SingleTierTopology}} do not generate unnecessary cross-tier touches.
> * {{touch()}} does not affect cache hit/miss statistics.
> * Existing {{CacheEngine}} implementations remain compatible through the default no-op implementation.



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