HBase：HBase如何知道一行是否包含特定的列

Question

HBase如何知道一行是否包含特定的列？例如，考虑以下情况：

null

Scan s = new Scan();
s.setStartRow ( Bytes.toBytes(“R1”) );
s.setStopRow ( Bytes.toBytes(“R2”) );
s.addColumn( STAT_FAM, Bytes.toBytes(“S500”) );
s.addColumn( STAT_FAM, Bytes.toBytes(“S2500”) );

提前感谢！

Answer 1

Hfile的KeyValue由以下内容组成：

<keylength> <valuelength> <key> <value>

键分解为：

<rowlength> <row> <columnfamilylength> <columnfamily> <columnqualifier> <timestamp> <keytype>

它将在一起

<keylength> <valuelength> <key> <rowlength> <row> <columnfamilylength> <columnfamily> <columnqualifier> <timestamp> <keytype> <value>

类名：org.apache.hadoop.hbase.filter.SingleColumnValueFilter

if (!keyValue.matchingColumn(this.columnFamily, this.columnQualifier)) {
      return ReturnCode.INCLUDE;
    }

if (filterColumnValue(keyValue.getBuffer(), keyValue.getValueOffset(), keyValue.getValueLength())) {
      return this.latestVersionOnly? ReturnCode.NEXT_ROW: ReturnCode.INCLUDE;
}

和org.apache.hadoop.hbase.KeyValue类。

  /**
   *
   * @param family column family
   * @param qualifier column qualifier
   * @return True if column matches
   */
  public boolean matchingColumn(final byte[] family, final byte[] qualifier) {
    int rl = getRowLength();
    int o = getFamilyOffset(rl);
    int fl = getFamilyLength(o);
    int ql = getQualifierLength(rl,fl);
    if (!Bytes.equals(family, 0, family.length, this.bytes, o, fl)) {
      return false;
    }
    if (qualifier == null || qualifier.length == 0) {
      if (ql == 0) {
        return true;
      }
      return false;
    }
    return Bytes.equals(qualifier, 0, qualifier.length,
        this.bytes, o + fl, ql);
  }


Image credit: Cloudera-blog