Table partitioning, bucketing and sort ordering

Table partitioning

To create a partitioned table, you should provide the following two components to construct a valid partitioned table.

• Partitioning strategy. It defines how Gravitino distributes table data across partitions. Currently, Gravitino supports the following partitioning strategies.

note

The score, createTime, and city appearing in the table below refer to the field names in a table.

Partitioning strategy	Description	JSON example	Java example	Equivalent SQL semantics
identity	Source value, unmodified.	{"strategy":"identity","fieldName":["score"]}	Transforms.identity("score")	PARTITION BY score
hour	Extract a timestamp hour, as hours from '1970-01-01 00:00:00'.	{"strategy":"hour","fieldName":["createTime"]}	Transforms.hour("createTime")	PARTITION BY hour(createTime)
day	Extract a date or timestamp day, as days from '1970-01-01'.	{"strategy":"day","fieldName":["createTime"]}	Transforms.day("createTime")	PARTITION BY day(createTime)
month	Extract a date or timestamp month, as months from '1970-01-01'	{"strategy":"month","fieldName":["createTime"]}	Transforms.month("createTime")	PARTITION BY month(createTime)
year	Extract a date or timestamp year, as years from 1970.	{"strategy":"year","fieldName":["createTime"]}	Transforms.year("createTime")	PARTITION BY year(createTime)
bucket[N]	Hash of value, mod N.	{"strategy":"bucket","numBuckets":10,"fieldNames":[["score"]]}	Transforms.bucket(10, "score")	PARTITION BY bucket(10, score)
truncate[W]	Value truncated to width W.	{"strategy":"truncate","width":20,"fieldName":["score"]}	Transforms.truncate(20, "score")	PARTITION BY truncate(20, score)
list	Partition the table by a list value.	{"strategy":"list","fieldNames":[["createTime"],["city"]]}	Transforms.list(new String[] {"createTime", "city"})	PARTITION BY list(createTime, city)
range	Partition the table by a range value.	{"strategy":"range","fieldName":["createTime"]}	Transforms.range("createTime")	PARTITION BY range(createTime)

As well as the strategies mentioned before, you can use other functions strategies to partition the table, for example, the strategy can be {"strategy":"functionName","fieldName":["score"]}. The functionName can be any function name that you can use in SQL, for example, {"strategy":"toDate","fieldName":["createTime"]} is equivalent to PARTITION BY toDate(createTime) in SQL. For complex functions, please refer to FunctionPartitioningDTO.

• Field names: It defines which fields Gravitino uses to partition the table.

• In some cases, you require other information. For example, if the partitioning strategy is bucket, you should provide the number of buckets; if the partitioning strategy is truncate, you should provide the width of the truncate.

The following is an example of creating a partitioned table:

Json

[
  {
    "strategy": "identity",
    "fieldName": ["score"]
  }
]

Java

new Transform[] {
    // Partition by score
    Transforms.identity("score")
    }

Table bucketing

To create a bucketed table, you should use the following three components to construct a valid bucketed table.

• Strategy. It defines how Gravitino distributes table data across partitions.

Bucket strategy	Description	JSON	Java
hash	Bucket table using hash. Gravitino distributes table data into buckets based on the hash value of the key.	hash	Strategy.HASH
range	Bucket table using range. Gravitino distributes table data into buckets based on a specified range or interval of values.	range	Strategy.RANGE
even	Bucket table using even. Gravitino distributes table data, ensuring an equal distribution of data.	even	Strategy.EVEN

• Number. It defines how many buckets you use to bucket the table.
• Function arguments. It defines the arguments of the strategy, Gravitino supports the following three kinds of arguments, for more, you can refer to Java class FunctionArg and DistributionDTO to use more complex function arguments.

Expression type	JSON example	Java example	Equivalent SQL semantics	Description
field	{"type":"field","fieldName":["score"]}	FieldReferenceDTO.of("score")	score	The field reference value score
function	{"type":"function","functionName":"hour","fieldName":["dt"]}	new FuncExpressionDTO.Builder().withFunctionName("hour").withFunctionArgs("dt").build()	hour(dt)	The function value hour(dt)
constant	{"type":"literal","value":10, "dataType": "integer"}	new LiteralDTO.Builder().withValue("10").withDataType(Types.IntegerType.get()).build()	10	The integer literal 10

Json

{
  "strategy": "hash",
  "number": 4,
  "funcArgs": [
    {
      "type": "field",
      "fieldName": ["score"]
    }
  ]
}

Java

Distributions.of(Strategy.HASH, 4, NamedReference.field("score"));

Sort ordering

To define a sorted order table, you should use the following three components to construct a valid sorted order table.

• Direction. It defines in which direction Gravitino sorts the table. The default value is ascending.

Direction	Description	JSON	Java
ascending	Sorted by a field or a function ascending.	asc	SortDirection.ASCENDING
descending	Sorted by a field or a function descending.	desc	SortDirection.DESCENDING

• Null ordering. It describes how to handle null values when ordering

Null ordering Type	Description	JSON	Java
null_first	Puts the null value in the first place.	nulls_first	NullOrdering.NULLS_FIRST
null_last	Puts the null value in the last place.	nulls_last	NullOrdering.NULLS_LAST

Note: If the direction value is ascending, the default ordering value is nulls_first and if the direction value is descending, the default ordering value is nulls_last.

• Sort term. It shows which field or function Gravitino uses to sort the table, please refer to the Function arguments in the table bucketing section.

Json

{
  "direction": "asc",
  "nullOrder": "NULLS_LAST",
  "sortTerm": {
    "type": "field",
    "fieldName": ["score"]
  }
}

Java

SortOrders.of(FieldReferenceDTO.of("score"), SortDirection.ASCENDING, NullOrdering.NULLS_LAST);

tip

Not all catalogs may support those features.. Please refer to the related document for more details.

The following is an example of creating a partitioned, bucketed table, and sorted order table:

Shell

curl -X POST -H "Accept: application/vnd.gravitino.v1+json" \
-H "Content-Type: application/json" -d '{
  "name": "table",
  "columns": [
    {
      "name": "id",
      "type": "integer",
      "nullable": true,
      "comment": "Id of the user"
    },
    {
      "name": "name",
      "type": "varchar(2000)",
      "nullable": true,
      "comment": "Name of the user"
    },
    {
      "name": "age",
      "type": "short",
      "nullable": true,
      "comment": "Age of the user"
    },
    {
      "name": "score",
      "type": "double",
      "nullable": true,
      "comment": "Score of the user"
    }
  ],
  "comment": "Create a new Table",
  "properties": {
    "format": "ORC"
  },
  "partitioning": [
    {
      "strategy": "identity",
      "fieldName": ["score"]
    }
  ],
  "distribution": {
    "strategy": "hash",
    "number": 4,
    "funcArgs": [
      {
        "type": "field",
        "fieldName": ["score"]
      }
    ]
  },
  "sortOrders": [
    {
      "direction": "asc",
      "nullOrder": "NULLS_LAST",
      "sortTerm":  {
        "type": "field",
        "fieldName": ["name"]
      }
    }
  ]
}' http://localhost:8090/api/metalakes/metalake/catalogs/catalog/schemas/schema/tables

Java

tableCatalog.createTable(
    NameIdentifier.of("metalake", "hive_catalog", "schema", "table"),
    new ColumnDTO[] {
      ColumnDTO.builder()
        .withComment("Id of the user")
        .withName("id")
        .withDataType(Types.IntegerType.get())
        .withNullable(true)
      .build(),
      ColumnDTO.builder()
        .withComment("Name of the user")
        .withName("name")
        .withDataType(Types.VarCharType.of(1000))
        .withNullable(true)
        .build(),
      ColumnDTO.builder()
        .withComment("Age of the user")
        .withName("age")
        .withDataType(Types.ShortType.get())
        .withNullable(true)
        .build(),
      ColumnDTO.builder()
        .withComment("Score of the user")
        .withName("score")
        .withDataType(Types.DoubleType.get())
        .withNullable(true)
        .build(),
    },
    "Create a new Table",
    tablePropertiesMap,
    new Transform[] {
    // Partition by id
      Transforms.identity("score")
    },
    // CLUSTERED BY id
    Distributions.of(Strategy.HASH, 4, NamedReference.field("id")),,
    // SORTED BY name asc
    new SortOrder[] {
      SortOrders.of(
        NamedReference.field("age"), SortDirection.ASCENDING, NullOrdering.NULLS_LAST),
    });