HBASE-26083 L1 miss metric is always 0 when using CombinedBlockCache (#3474)

Signed-off-by Anoop Sam John <anoopsamjohn@apache.org>
Signed-off-by Reid Chan <reidchan@apache.org>

Author: YutSean

hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/CombinedBlockCache.java

@@ -79,7 +79,13 @@ public Cacheable getBlock(BlockCacheKey cacheKey, boolean caching,
       boolean repeat, boolean updateCacheMetrics) {
     // TODO: is there a hole here, or just awkwardness since in the lruCache getBlock
     // we end up calling l2Cache.getBlock.
-    return lruCache.containsBlock(cacheKey)?
+    boolean existInL1 = lruCache.containsBlock(cacheKey);
+    if (!existInL1 && updateCacheMetrics && !repeat) {
+      // If the block does not exist in L1, this check should be counted as a miss.
+      combinedCacheStats.lruCacheStats
+        .miss(caching, cacheKey.isPrimary(), cacheKey.getBlockType());
+    }
+    return existInL1 ?
         lruCache.getBlock(cacheKey, caching, repeat, updateCacheMetrics):
         l2Cache.getBlock(cacheKey, caching, repeat, updateCacheMetrics);
   }