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Datatypes

Datatypes and Fixed Encoding

This topic describes standard datatypes and space-saving variations for values stored in HEAVY.AI.

Datatypes

Each HEAVY.AI datatype uses space in memory and on disk. For certain datatypes, you can use fixed encoding for a more compact representation of these values. You can set a default value for a column by using the DEFAULT constraint; for more information, see CREATE TABLE.

Datatypes, variations, and sizes are described in the following table.

[1] - In HEAVY.AI release 4.4.0 and higher, you can use existing 8-byte DATE columns, but you can create only 4-byte DATE columns (default) and 2-byte DATE columns (see DATE ENCODING DAYS(16)).

[2] - See Storage and Compression below for information about geospatial datatype sizes.

HEAVY.AI does not support geometry arrays.
Timestamp values are always stored in 8 bytes. The greater the precision, the lower the fidelity.

Geospatial Datatypes

HEAVY.AI supports the LINESTRING, MULTILINESTRING, POLYGON, MULTIPOLYGON, POINT, and MULTIPOINT geospatial datatypes.

In the following example:

p0, p1, ls0, and poly0 are simple (planar) geometries.
p4 is point geometry with Web Mercator longitude/latitude coordinates.
p2, p3, mp, ls1, ls2, mls1, mls2, poly1, and mpoly0 are geometries using WGS84 SRID=4326 longitude/latitude coordinates.

CREATE TABLE geo ( name TEXT ENCODING DICT(32),
                   p0 POINT,
                   p1 GEOMETRY(POINT),
                   p2 GEOMETRY(POINT, 4326),
                   p3 GEOMETRY(POINT, 4326) ENCODING NONE,
                   p4 GEOMETRY(POINT, 900913),
                   mp GEOMETRY(MULTIPOINT, 4326),
                   ls0  LINESTRING,
                   ls1 GEOMETRY(LINESTRING, 4326) ENCODING COMPRESSED(32),
                   ls2 GEOMETRY(LINESTRING, 4326) ENCODING NONE,
                   mls1 GEOMETRY(MULTILINESTRING, 4326) ENCODING COMPRESSED(32),
                   mls2 GEOMETRY(MULTILINESTRING, 4326) ENCODING NONE,
                   poly0 POLYGON,
                   poly1 GEOMETRY(POLYGON, 4326) ENCODING COMPRESSED(32),
                   mpoly0 GEOMETRY(MULTIPOLYGON, 4326)
                  );

Storage

Geometry storage requirements are largely dependent on coordinate data. Coordinates are normally stored as 8-byte doubles, two coordinates per point, for all points that form a geometry. Each POINT geometry in the p1 column, for example, requires 16 bytes.

Compression

WGS84 (SRID 4326) coordinates are compressed to 32 bits by default. This sacrifices some precision but reduces storage requirements by half.

For example, columns p2, mp, ls1, mls1, poly1, and mpoly0 in the table defined above are compressed. Each geometry in the p2 column requires 8 bytes, compared to 16 bytes for p0.

You can explicitly disable compression. WGS84 columns p3, ls2, mls2 are not compressed and continue using doubles. Simple (planar) columns p0, p1, ls0, poly1 and non-4326 column p4 are not compressed.

For more information about geospatial datatypes and functions, see Geospatial Capabilities.

Defining Arrays

Define datatype arrays by appending square brackets, as shown in the arrayexamples DDL sample.

CREATE TABLE arrayexamples (
  tiny_int_array TINYINT[],
  int_array INTEGER[],
  big_int_array BIGINT[],
  text_array TEXT[] ENCODING DICT(32), --HeavyDB supports only DICT(32) TEXT arrays.
  float_array FLOAT[],
  double_array DOUBLE[],
  decimal_array DECIMAL(18,6)[],
  boolean_array BOOLEAN[],
  date_array DATE[],
  time_array TIME[],
  timestamp_array TIMESTAMP[])

You can also define fixed-length arrays. For example:

CREATE TABLE arrayexamples (
  float_array3 FLOAT[3],
  date_array4 DATE[4]

Fixed-length arrays require less storage space than variable-length arrays.

Fixed Encoding

To use fixed-length fields, the range of the data must fit into the constraints as described. Understanding your schema and the scope of potential values in each field helps you to apply fixed encoding types and save significant storage space.

These encodings are most effective on low-cardinality TEXT fields, where you can achieve large savings of storage space and improved processing speed, and on TIMESTAMP fields where the timestamps range between 1901-12-13 20:45:53 and 2038-01-19 03:14:07. If a TEXT ENCODING field does not match the defined cardinality, HEAVY.AI substitutes a NULL value and logs the change.

For DATE types, you can use the terms FIXED and DAYS interchangeably. Both are synonymous for the DATE type in HEAVY.AI.

Some of the INTEGER options overlap. For example, INTEGER ENCODINGFIXED(8) and SMALLINT ENCODINGFIXED(8) are essentially identical.

Shared Dictionaries

You can improve performance of string operations and optimize storage using shared dictionaries. You can share dictionaries within a table or between different tables in the same database. The table with which you want to share dictionaries must exist when you create the table that references the TEXT ENCODING DICT field, and the column that you are referencing in that table must also exist. The following small DDL shows the basic structure:

CREATE TABLE text_shard (
i TEXT ENCODING DICT(32),
s TEXT ENCODING DICT(32),
SHARD KEY (i))
WITH (SHARD_COUNT = 2);

CREATE TABLE text_shard1 (
i TEXT,
s TEXT ENCODING DICT(32),
SHARD KEY (i),
SHARED DICTIONARY (i) REFERENCES text_shard(i))
WITH (SHARD_COUNT = 2);

In the table definition, make sure that referenced columns appear before the referencing columns.

For example, this DDL is a portion of the schema for the flights database. Because airports are both origin and destination locations, it makes sense to reuse the same dictionaries for name, city, state, and country values.

create table flights (
*
*
*
dest_name TEXT ENCODING DICT,
dest_city TEXT ENCODING DICT,
dest_state TEXT ENCODING DICT,
dest_country TEXT ENCODING DICT,

*
*
*
origin_name TEXT,
origin_city TEXT,
origin_state TEXT,
origin_country TEXT,
*
*
*

SHARED DICTIONARY (origin_name) REFERENCES flights(dest_name),
SHARED DICTIONARY (origin_city) REFERENCES flights(dest_city),
SHARED DICTIONARY (origin_state) REFERENCES flights(dest_state),
SHARED DICTIONARY (origin_country) REFERENCES flights(dest_country),
*
*
*
)
WITH(
*
*
*
)

To share a dictionary in a different existing table, replace the table name in the REFERENCES instruction. For example, if you have an existing table called us_geography, you can share the dictionary by following the pattern in the DDL fragment below.

create table flights (

*
*
*

SHARED DICTIONARY (origin_city) REFERENCES us_geography(city),
SHARED DICTIONARY (origin_state) REFERENCES us_geography(state),
SHARED DICTIONARY (origin_country) REFERENCES us_geography(country),
SHARED DICTIONARY (dest_city) REFERENCES us_geography(city),
SHARED DICTIONARY (dest_state) REFERENCES us_geography(state),
SHARED DICTIONARY (dest_country) REFERENCES us_geography(country),

*
*
*
)
WITH(
*
*
*
);

The referencing column cannot specify the encoding of the dictionary, because it uses the encoding from the referenced column.

Datatypes

Datatypes and Fixed Encoding

This topic describes standard datatypes and space-saving variations for values stored in HEAVY.AI.

Datatypes

Datatypes, variations, and sizes are described in the following table.

[2] - See Storage and Compression below for information about geospatial datatype sizes.

HEAVY.AI does not support geometry arrays.
Timestamp values are always stored in 8 bytes. The greater the precision, the lower the fidelity.

Geospatial Datatypes

HEAVY.AI supports the LINESTRING, MULTILINESTRING, POLYGON, MULTIPOLYGON, POINT, and MULTIPOINT geospatial datatypes.

In the following example:

p0, p1, ls0, and poly0 are simple (planar) geometries.
p4 is point geometry with Web Mercator longitude/latitude coordinates.
p2, p3, mp, ls1, ls2, mls1, mls2, poly1, and mpoly0 are geometries using WGS84 SRID=4326 longitude/latitude coordinates.

CREATE TABLE geo ( name TEXT ENCODING DICT(32),
                   p0 POINT,
                   p1 GEOMETRY(POINT),
                   p2 GEOMETRY(POINT, 4326),
                   p3 GEOMETRY(POINT, 4326) ENCODING NONE,
                   p4 GEOMETRY(POINT, 900913),
                   mp GEOMETRY(MULTIPOINT, 4326),
                   ls0  LINESTRING,
                   ls1 GEOMETRY(LINESTRING, 4326) ENCODING COMPRESSED(32),
                   ls2 GEOMETRY(LINESTRING, 4326) ENCODING NONE,
                   mls1 GEOMETRY(MULTILINESTRING, 4326) ENCODING COMPRESSED(32),
                   mls2 GEOMETRY(MULTILINESTRING, 4326) ENCODING NONE,
                   poly0 POLYGON,
                   poly1 GEOMETRY(POLYGON, 4326) ENCODING COMPRESSED(32),
                   mpoly0 GEOMETRY(MULTIPOLYGON, 4326)
                  );

Storage

Compression

WGS84 (SRID 4326) coordinates are compressed to 32 bits by default. This sacrifices some precision but reduces storage requirements by half.

For example, columns p2, mp, ls1, mls1, poly1, and mpoly0 in the table defined above are compressed. Each geometry in the p2 column requires 8 bytes, compared to 16 bytes for p0.

For more information about geospatial datatypes and functions, see Geospatial Capabilities.

Defining Arrays

Define datatype arrays by appending square brackets, as shown in the arrayexamples DDL sample.

CREATE TABLE arrayexamples (
  tiny_int_array TINYINT[],
  int_array INTEGER[],
  big_int_array BIGINT[],
  text_array TEXT[] ENCODING DICT(32), --HeavyDB supports only DICT(32) TEXT arrays.
  float_array FLOAT[],
  double_array DOUBLE[],
  decimal_array DECIMAL(18,6)[],
  boolean_array BOOLEAN[],
  date_array DATE[],
  time_array TIME[],
  timestamp_array TIMESTAMP[])

You can also define fixed-length arrays. For example:

CREATE TABLE arrayexamples (
  float_array3 FLOAT[3],
  date_array4 DATE[4]

Fixed-length arrays require less storage space than variable-length arrays.

Fixed Encoding

For DATE types, you can use the terms FIXED and DAYS interchangeably. Both are synonymous for the DATE type in HEAVY.AI.

Some of the INTEGER options overlap. For example, INTEGER ENCODINGFIXED(8) and SMALLINT ENCODINGFIXED(8) are essentially identical.

Shared Dictionaries

CREATE TABLE text_shard (
i TEXT ENCODING DICT(32),
s TEXT ENCODING DICT(32),
SHARD KEY (i))
WITH (SHARD_COUNT = 2);

CREATE TABLE text_shard1 (
i TEXT,
s TEXT ENCODING DICT(32),
SHARD KEY (i),
SHARED DICTIONARY (i) REFERENCES text_shard(i))
WITH (SHARD_COUNT = 2);

In the table definition, make sure that referenced columns appear before the referencing columns.

create table flights (
*
*
*
dest_name TEXT ENCODING DICT,
dest_city TEXT ENCODING DICT,
dest_state TEXT ENCODING DICT,
dest_country TEXT ENCODING DICT,

*
*
*
origin_name TEXT,
origin_city TEXT,
origin_state TEXT,
origin_country TEXT,
*
*
*

SHARED DICTIONARY (origin_name) REFERENCES flights(dest_name),
SHARED DICTIONARY (origin_city) REFERENCES flights(dest_city),
SHARED DICTIONARY (origin_state) REFERENCES flights(dest_state),
SHARED DICTIONARY (origin_country) REFERENCES flights(dest_country),
*
*
*
)
WITH(
*
*
*
)

create table flights (

*
*
*

SHARED DICTIONARY (origin_city) REFERENCES us_geography(city),
SHARED DICTIONARY (origin_state) REFERENCES us_geography(state),
SHARED DICTIONARY (origin_country) REFERENCES us_geography(country),
SHARED DICTIONARY (dest_city) REFERENCES us_geography(city),
SHARED DICTIONARY (dest_state) REFERENCES us_geography(state),
SHARED DICTIONARY (dest_country) REFERENCES us_geography(country),

*
*
*
)
WITH(
*
*
*
);

The referencing column cannot specify the encoding of the dictionary, because it uses the encoding from the referenced column.