BlockCacheKey cacheKey = new BlockCacheKey(name, dataBlockOffset);
boolean useLock = false;
IdLock.Entry lockEntry = null;
TraceScope traceScope = Trace.startSpan("HFileReaderV2.readBlock");
try {
while (true) {
if (useLock) {
lockEntry = offsetLock.getLockEntry(dataBlockOffset);
}
// Check cache for block. If found return.
if (cacheConf.isBlockCacheEnabled()) {
// Try and get the block from the block cache. If the useLock variable is true then this
// is the second time through the loop and it should not be counted as a block cache miss.
HFileBlock cachedBlock = getCachedBlock(cacheKey, cacheBlock, useLock, isCompaction,
updateCacheMetrics, expectedBlockType, expectedDataBlockEncoding);
if (cachedBlock != null) {
assert cachedBlock.isUnpacked() : "Packed block leak.";
if (cachedBlock.getBlockType().isData()) {
if (updateCacheMetrics) {
HFile.dataBlockReadCnt.incrementAndGet();
}
// Validate encoding type for data blocks. We include encoding
// type in the cache key, and we expect it to match on a cache hit.
if (cachedBlock.getDataBlockEncoding() != dataBlockEncoder.getDataBlockEncoding()) {
throw new IOException("Cached block under key " + cacheKey + " "
+ "has wrong encoding: " + cachedBlock.getDataBlockEncoding() + " (expected: "
+ dataBlockEncoder.getDataBlockEncoding() + ")");
}
}
return cachedBlock;
}
// Carry on, please load.
}
if (!useLock) {
// check cache again with lock
useLock = true;
continue;
}
if (Trace.isTracing()) {
traceScope.getSpan().addTimelineAnnotation("blockCacheMiss");
}
// Load block from filesystem.
HFileBlock hfileBlock = fsBlockReader.readBlockData(dataBlockOffset, onDiskBlockSize, -1,
pread);
validateBlockType(hfileBlock, expectedBlockType);
HFileBlock unpacked = hfileBlock.unpack(hfileContext, fsBlockReader);
BlockType.BlockCategory category = hfileBlock.getBlockType().getCategory();
// Cache the block if necessary
if (cacheBlock && cacheConf.shouldCacheBlockOnRead(category)) {
cacheConf.getBlockCache().cacheBlock(cacheKey,
cacheConf.shouldCacheCompressed(category) ? hfileBlock : unpacked,
cacheConf.isInMemory(), this.cacheConf.isCacheDataInL1());
}
if (updateCacheMetrics && hfileBlock.getBlockType().isData()) {
HFile.dataBlockReadCnt.incrementAndGet();
}
return unpacked;
}
} finally {
traceScope.close();
if (lockEntry != null) {
offsetLock.releaseLockEntry(lockEntry);
}
}
}