saintstack commented on a change in pull request #3407:
URL: https://github.com/apache/hbase/pull/3407#discussion_r671532481
##########
File path:
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruAdaptiveBlockCache.java
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@@ -646,14 +639,16 @@ private long updateSizeMetrics(LruCachedBlock cb, boolean
evict) {
@Override
public Cacheable getBlock(BlockCacheKey cacheKey, boolean caching, boolean
repeat,
boolean updateCacheMetrics) {
- LruCachedBlock cb = map.computeIfPresent(cacheKey, (key, val) -> {
- // 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.
- // see HBASE-22422.
- val.getBuffer().retain();
- return val;
- });
+ LruCachedBlock cb = map.get(cacheKey);
+ if (cb != null) {
+ try {
+ cb.getBuffer().retain();
Review comment:
Looking at this more.... I don't think we can do your trick afterall.
The refcounting is not for the cache, it is for a backing pool of memory
used reading data in from hdfs into the cache. When we evict a block from the
cache, we call #release on the memory. If the refcount is zero, the memory is
released and can be reused in the backing pool. If #release is called and the
#refcount is not zero, we just decrement the refcount.
A cached buffer item detached from the cache still needs to have its
#release called w/ refcount at zero so the backing memory gets readded to the
pool.
So it seems to me. What you think @virajjasani
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