Enabling a Term Index When Creating a Table

Updated on 2024-11-28 GMT+08:00

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Function Description

Follow instructions in Creating a Table to create a table. In addition, configure a term index schema in table properties.

Sample Code

public void testCreateTable() {
  LOG.info("Entering testCreateTable.");
  HTableDescriptor tableDesc = new HTableDescriptor(tableName);
  HColumnDescriptor cdm = new HColumnDescriptor(FAM_M);
  cdm.setDataBlockEncoding(DataBlockEncoding.FAST_DIFF);
  tableDesc.addFamily(cdm);
  HColumnDescriptor cdn = new HColumnDescriptor(FAM_N);
  cdn.setDataBlockEncoding(DataBlockEncoding.FAST_DIFF);
  tableDesc.addFamily(cdn);

  // Add bitmap index definitions.
  List<BitmapIndexDescriptor> bitmaps = new ArrayList<>();//(1)
  bitmaps.add(BitmapIndexDescriptor.builder()
    // Describe which column should be indexed.
    .setColumnName(FamilyOnlyName.valueOf(FAM_M))//(2)
    // Describe how to extract term(s) from KeyValue
    .setTermExtractor(TermExtractor.NAME_VALUE_EXTRACTOR)//(3)
    .build());
  // It will help to add several properties into HTableDescriptor.
  // SHARD_NUM should be less than the region number
  IndexHelper.enableAutoIndex(tableDesc, SHARD_NUM, bitmaps);//(4)

  List<byte[]> splitList = Arrays.stream(SPLIT.split(LemonConstants.COMMA))
    .map(s -> org.lemon.common.Bytes.toBytes(s.trim()))
    .collect(Collectors.toList());
  byte[][] splitArray = splitList.toArray(new byte[splitList.size()][]);

  Admin admin = null;
  try {
    // Instantiate an Admin object.
    admin = conn.getAdmin();
    if (!admin.tableExists(tableName)) {
      LOG.info("Creating table...");
      admin.createTable(tableDesc, splitArray);
      LOG.info(admin.getClusterStatus());
      LOG.info(admin.listNamespaceDescriptors());
      LOG.info("Table created successfully.");
    } else {
      LOG.warn("table already exists");
    }
  } catch (IOException e) {
    LOG.error("Create table failed.", e);
  } finally {
    if (admin != null) {
      try {
        // Close the Admin object.
        admin.close();
      } catch (IOException e) {
        LOG.error("Failed to close admin ", e);
      }
    }
  }
  LOG.info("Exiting testCreateTable.");
}

Precautions

(1) BitmapIndexDescriptor describes which fields use what rules to extract terms. One or more BitmapIndexDescriptor can be defined in a data table.
(2) Defines which columns need to extract terms. The options are as follows:
- ExplicitColumnName: Specifies a column.
- FamilyOnlyName: Indicates all columns in a column family.
- PrefixColumnName: Indicates columns with a specific prefix.
(3) Defines a rule for extracting terms from columns. The options are as follows:
- QualifierExtractor: Indicates that terms are extracted by column name.
  For example, if qualifier is Male and value is 1, the extracted term is Male.
- QualifierValueExtractor: Indicates that terms are extracted by column name and value.
  For example, if qualifier is education and value is master, the extracted term is education:master.
- QualifierArrayValueExtractor: Indicates that multiple terms can be extracted. The value is in JSON array format.
  For example, if qualifier is hobby and value is ["basketball","football","volleyball"], the extracted terms are as follows:
```
hobby:basketball
hobby:football
hobby:volleyball
```
- QualifierMapValueExtractor: Indicates that multiple terms can be extracted. The value is in JSON map format.
  For example, if qualifier is hobby and value is {"basketball":"9","football":"8","volleyball":"7"}, the extracted terms are as follows:
```
hobby:basketball
hobby:football
hobby:volleyball
hobby:basketball_9
hobby:football_8
hobby:volleyball_7
```
(4) The number of shards (SHARD_NUM) in the index table must be less than or equal to that in the data table.

Parent topic: Sample Code Description

Previous topic: Creating the Configuration Object

Next topic: Writing Data

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