Hbase 布隆过滤器BloomFilter介绍

if (!scan.isGetScan()) {  
        return true;  
}  
byte[] row = scan.getStartRow();  
switch (this.bloomFilterType) {  
  case ROW:  
    return passesBloomFilter(row, 0, row.length, null, 0, 0);  
 
  case ROWCOL:  
    if (columns != null && columns.size() == 1) {  
      byte[] column = columns.first();  
      return passesBloomFilter(row, 0, row.length, column, 0, column.length);  
    }  
    // For multi-column queries the Bloom filter is checked from the  
    // seekExact operation.  
    return true;  
 
  default:  
    return true;
}

// Seek all scanners to the start of the Row (or if the exact matching row  
// key does not exist, then to the start of the next matching Row).  
if (matcher.isExactColumnQuery()) {  
  for (KeyValueScanner scanner : scanners)  
  scanner.seekExactly(matcher.getStartKey(), false);  
} else {  
  for (KeyValueScanner scanner : scanners)  
  scanner.seek(matcher.getStartKey());  
}

public boolean seekExactly(KeyValue kv, boolean forward)  
      throws IOException {  
    if (reader.getBloomFilterType() != StoreFile.BloomType.ROWCOL ||  
        kv.getRowLength() == 0 || kv.getQualifierLength() == 0) {  
      return forward ? reseek(kv) : seek(kv);  
    }  
  
    boolean isInBloom = reader.passesBloomFilter(kv.getBuffer(),  
        kv.getRowOffset(), kv.getRowLength(), kv.getBuffer(),  
        kv.getQualifierOffset(), kv.getQualifierLength());  
    if (isInBloom) {  
      // This row/column might be in this store file. Do a normal seek.  
      return forward ? reseek(kv) : seek(kv);  
    }  
  
    // Create a fake key/value, so that this scanner only bubbles up to the top  
    // of the KeyValueHeap in StoreScanner after we scanned this row/column in  
    // all other store files. The query matcher will then just skip this fake  
    // key/value and the store scanner will progress to the next column.  
    cur = kv.createLastOnRowCol();  
    return true;  
}

由于Bloom Filter是须要事先知道过滤项的。对于顺序scan是没有事先办法知道rowkey的。

而get是指明了rowkey所以能够用Bloom Filter，scan指明column同理。