saintstack commented on a change in pull request #3215:
URL: https://github.com/apache/hbase/pull/3215#discussion_r638044447
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File path:
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/TinyLfuBlockCache.java
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@@ -158,7 +158,13 @@ public boolean containsBlock(BlockCacheKey cacheKey) {
@Override
public Cacheable getBlock(BlockCacheKey cacheKey,
boolean caching, boolean repeat, boolean updateCacheMetrics) {
- Cacheable value = cache.getIfPresent(cacheKey);
+ Cacheable value = cache.asMap().computeIfPresent(cacheKey, (blockCacheKey,
cacheable) -> {
+ // It will be referenced by RPC path, so increase here. NOTICE: Must do
the retain inside
+ // this block. because if retain outside the map#computeIfPresent, the
evictBlock may remove
+ // the block and release, then we're retaining a block with refCnt=0
which is disallowed.
+ cacheable.retain();
+ return cacheable;
+ });
Review comment:
Smile. Related. I've been studying at this bit of code here.. the flip
to computeIfPresent. #get in CHM is lockless but computeIfPresent takes a lock
on the bucket (of keys) so seems to slow us down especially if high read load
with most data in cache; e.g. meta hits.
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