VladRodionov commented on code in PR #8575:
URL: https://github.com/apache/hbase/pull/8575#discussion_r3890464489
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hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/cache/DefaultHBaseCachePlacementAdmissionPolicy.java:
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@@ -60,7 +63,7 @@ public TierDecision selectTier(BlockCacheKey cacheKey,
Cacheable block, CacheWri
* L2 when both tiers are available, but falls back to any available tier
rather than rejecting
* placement.
*/
- if (topologyView.getType() == CacheTopologyType.SINGLE) {
+ if (topologyView.getType() == CacheTopologyType.SINGLE_TIER) {
return TierDecision.single(CacheTier.SINGLE);
Review Comment:
I think keeping `CacheTier.SINGLE` is intentional here.
`SINGLE_TIER` describes topology cardinality: there is only one active cache
engine. That engine is
not necessarily semantically L1. For example, a configuration may use only
`BucketCache`, in which
case treating the only engine as L1 would be misleading.
So the model is:
* `CacheTopologyType.SINGLE_TIER` uses `CacheTier.SINGLE`
* `CacheTopologyType.TIERED_EXCLUSIVE` uses `CacheTier.L1` and `CacheTier.L2`
* `CacheTopologyType.TIERED_INCLUSIVE` uses `CacheTier.L1` and `CacheTier.L2`
I updated the single-tier code paths to consistently resolve
`CacheTier.SINGLE`.
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