[jira] [Created] (HBASE-30305) Replace CombinedBlockCache orchestration with TieredExclusiveTopology-backed CacheAccessService

["Vladimir Rodionov (Jira)" <ji...@apache.org>]

Vladimir Rodionov created HBASE-30305:
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             Summary: Replace CombinedBlockCache orchestration with TieredExclusiveTopology-backed CacheAccessService
                 Key: HBASE-30305
                 URL: https://issues.apache.org/jira/browse/HBASE-30305
             Project: HBase
          Issue Type: New Feature
          Components: BlockCache, Performance
    Affects Versions: 4.0.0-alpha-1
            Reporter: Vladimir Rodionov
            Assignee: Vladimir Rodionov


h3. Description

HBASE-30024 introduced BlockCacheBackedCacheEngine, allowing existing BlockCache
implementations to participate as CacheEngine instances.

HBASE-30025 added the construction path for creating a TopologyBackedCacheAccessService
from existing L1 and L2 BlockCache instances using TieredExclusiveTopology.

The next step is to replace CombinedBlockCache as the primary L1/L2 orchestration object
used by CacheAccessService.

Today, the combined block cache path is assembled as:

  LruBlockCache + BucketCache
    -> CombinedBlockCache
        -> BlockCacheBackedCacheAccessService

This ticket should change the CacheAccessService construction path to use:

  LruBlockCache + BucketCache
    -> BlockCacheBackedCacheEngine
        -> TieredExclusiveTopology
            -> TopologyBackedCacheAccessService

CombinedBlockCache should not be removed in this ticket. It should remain available for
legacy APIs, diagnostics, tests, and any code paths that still require a BlockCache instance.
However, new cache access should no longer depend on CombinedBlockCache for tiered
orchestration.

The goal is to make TieredExclusiveTopology the primary orchestration model for the
combined L1/L2 cache path while preserving existing behavior and keeping CombinedBlockCache
as a compatibility object.
h3. Scope

* Change CacheConfig / BlockCacheFactory construction so CacheAccessService for combined
  L1/L2 cache uses TopologyBackedCacheAccessService.

* Reuse TopologyBackedCacheAccessServices.fromTieredExclusiveBlockCaches(...).

* Keep LruBlockCache and BucketCache as existing BlockCache implementations underneath.

* Keep CombinedBlockCache class in the source tree.

* Keep any existing BlockCache-returning APIs working if they still need to expose a
  CombinedBlockCache or legacy BlockCache view.

* Add tests proving the CacheAccessService path no longer wraps CombinedBlockCache when
  L1/L2 combined cache is enabled.

* Add compatibility tests proving the old BlockCache view, if still exposed, remains usable.
h3. Out of scope

* Do not delete CombinedBlockCache.
* Do not migrate LruBlockCache or BucketCache to implement CacheEngine directly yet.
* Do not remove BlockCacheBackedCacheAccessService.
* Do not migrate JSP/admin diagnostics yet unless required by compilation.
* Do not remove CombinedBlockCache tests yet.



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