近日，觀察到HBase集群出現如下WARN日誌： 2020 04 18 16:17:03,081 WARN [regionserver/xxx BucketCacheWriter 1] bucket.BucketCache:Failed allocation for 604acc82edd349ca ...
近日，觀察到HBase集群出現如下WARN日誌：
2020-04-18 16:17:03,081 WARN [regionserver/xxx-BucketCacheWriter-1] bucket.BucketCache:Failed allocation for 604acc82edd349ca906939af14464bcb_175674734;
org.apache.hadoop.hbase.io.hfile.bucket.BucketAllocatorException: Allocation too big size=1114202; adjust BucketCache sizes hbase.bucketcache.bucket.sizes to accomodate if size seems reasonable and you want it cached.
大概意思是說：由於block塊太大（size=1114202）導致BucketAllocator無法為其分配空間，如果想要被緩存並且覺得這樣做合理，可以調整參數hbase.bucketcache.bucket.sizes。
預設情況下，HBase BucketCache 能夠緩存block的最大值為512KB，即hbase.bucketcache.bucket.sizes=5120,9216,17408,33792,41984,50176,58368,66560,99328,132096,197632,263168,394240,525312，預設14種size標簽。如果想要緩存更大的block塊，我們可以調整參數為 hbase.bucketcache.bucket.sizes=5120,9216,17408,33792,41984,50176,58368,66560,99328,132096,197632,263168,394240,525312,1049600,2098176，此時最大容許2MB的block。
下麵我們簡單看一下對應源代碼，涉及相關類為：
/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketAllocator.java
BucketAllocator主要實現對bucket的組織管理，為block分配記憶體空間。
/**
* Allocate a block with specified size. Return the offset
* @param blockSize size of block
* @throws BucketAllocatorException
* @throws CacheFullException
* @return the offset in the IOEngine
*/
public synchronized long allocateBlock(int blockSize) throws CacheFullException,
BucketAllocatorException {
assert blockSize > 0;
BucketSizeInfo bsi = roundUpToBucketSizeInfo(blockSize);
if (bsi == null) {
throw new BucketAllocatorException("Allocation too big size=" + blockSize +
"; adjust BucketCache sizes " + BlockCacheFactory.BUCKET_CACHE_BUCKETS_KEY +
" to accomodate if size seems reasonable and you want it cached.");
}
long offset = bsi.allocateBlock();
// Ask caller to free up space and try again!
if (offset < 0)
throw new CacheFullException(blockSize, bsi.sizeIndex());
usedSize += bucketSizes[bsi.sizeIndex()];
return offset;
}
在調用roundUpToBucketSizeInfo()方法後，返回結果如果為null則拋出BucketAllocatorException異常。看一下roundUpToBucketSizeInfo()方法：
/**
* Round up the given block size to bucket size, and get the corresponding
* BucketSizeInfo
*/
public BucketSizeInfo roundUpToBucketSizeInfo(int blockSize) {
for (int i = 0; i < bucketSizes.length; ++i)
if (blockSize <= bucketSizes[i])
return bucketSizeInfos[i];
return null;
}
該方法將傳入的blockSize與數組bucketSizes從索引0開始取值進行比較，一旦小於bucketSize[i]，則為該block分配bucketSizeInfos[i]大小的空間存放該block。
我們看一下數組bucketSizes的初始化過程：
private static final int DEFAULT_BUCKET_SIZES[] = { 4 * 1024 + 1024, 8 * 1024 + 1024,
16 * 1024 + 1024, 32 * 1024 + 1024, 40 * 1024 + 1024, 48 * 1024 + 1024,
56 * 1024 + 1024, 64 * 1024 + 1024, 96 * 1024 + 1024, 128 * 1024 + 1024,
192 * 1024 + 1024, 256 * 1024 + 1024, 384 * 1024 + 1024,
512 * 1024 + 1024 };
private final int[] bucketSizes;
BucketAllocator(long availableSpace, int[] bucketSizes)
throws BucketAllocatorException {
this.bucketSizes = bucketSizes == null ? DEFAULT_BUCKET_SIZES : bucketSizes;
Arrays.sort(this.bucketSizes);
...
}
可以看到，如果bucketSizes == null預設取數組DEFAULT_BUCKET_SIZES的值，並對該數組進行排序。這一步的排序為上一步的迴圈比較奠定了基礎。
而數組DEFAULT_BUCKET_SIZES的值，也就是參數hbase.bucketcache.bucket.sizes的預設值。
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