virajjasani commented on a change in pull request #3407:
URL: https://github.com/apache/hbase/pull/3407#discussion_r666473427
##########
File path:
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruAdaptiveBlockCache.java
##########
@@ -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:
It is purged from cache by:
```
protected long evictBlock(LruCachedBlock block, boolean
evictedByEvictionProcess) {
LruCachedBlock previous = map.remove(block.getCacheKey()); =======>
removed from map
if (previous == null) {
return 0;
}
updateSizeMetrics(block, true);
long val = elements.decrementAndGet();
if (LOG.isTraceEnabled()) {
long size = map.size();
assertCounterSanity(size, val);
}
if (block.getBuffer().getBlockType().isData()) {
dataBlockElements.decrement();
}
if (evictedByEvictionProcess) {
// When the eviction of the block happened because of invalidation of
HFiles, no need to
// update the stats counter.
stats.evicted(block.getCachedTime(), block.getCacheKey().isPrimary());
if (victimHandler != null) {
victimHandler.cacheBlock(block.getCacheKey(), block.getBuffer());
}
}
// Decrease the block's reference count, and if refCount is 0, then
it'll auto-deallocate. DO
// NOT move this up because if do that then the victimHandler may access
the buffer with
// refCnt = 0 which is disallowed.
previous.getBuffer().release(); ============================>
buffer released
return block.heapSize();
}
```
Based on above mentioned eviction code, we have below mentioned
possibilities when eviction and getBlock happens for the same block at the same
time:
1. getBlock retrieves block from map, eviction removes it from map, eviction
does release(), getBlock does retain() and encounters IllegalRefCount
Exception, we handler it with this patch and treat it as cache miss.
2. getBlock retrieves block from map, eviction removes it from map, getBlock
does retain(), eviction does release(). Since getBlock retain() was successful,
it proceeds as successful cache hit, which happens even today with
computeIfPresent. Subsequent getBlock call will return null as block was
evicted previously.
3. eviction removes from map, getBlock gets null, it's clear cache miss.
I think we seem good here. WDYT @saintstack?
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