Details
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New Feature
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Status: Closed
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Major
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Resolution: Fixed
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None
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None
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Important
Description
This proposal is to add support for multiple column families in trafodion tables. With this feature, one can store columns into multiple column families. One use for this would be to store frequently used columns in one column family and infrequently used columns to be stored in a different column family. That will have performance improvement when those columns are retrieved from hbase. There could be other uses as well.
Syntax:
create table <tablename> ( <colFam1>.<colName1> <datatype>, <colFam2>.<colName2> <datatype> ….)
attributes default column family <colFam>;
alter table <tablename> add column <colFam>.<colName> datatype;
<colFam> : name of column family for that column
Semantics:
<colFam> name follows identifier rules. If not double quoted, then it will be upper cased. If double quoted, then case will be maintained.
User specified column family can be of arbitrary length. To optimize space for column family stored in a cell, a 2 byte encoding is generated.
Mapping of user specified column family to encoded column family is stored in metadata.
If no column family is specified for a column during create table, then the family specified in ‘attributes default column family’ clause is used.
If no ‘attribute default column family’ clause is specified , then system default col family is used.
column family specification is supported for regular and volatile tables.
all unique column families specified during create or alter are added to the table
maximum number of column families supported in one table is 32. But it is hbase recommendation to not create too many column families.
alter statement can be used to assign specific hbase options to specific column families
using the NAME clause. If no name clause is specified, then alter hbase options are applied
to all col families.
invoke and showddl statements will show the original user specified column families and not the encoded column families
Currently, multiple column families are not supported for columns of a user created or an implicitly created index.
The default column family of the corresponding base table is used for all index columns.
column family cannot be specified in a DML query
column family cannot be specified for columns of an aligned row format table since all columns are stored as one cell
Column names must be unique for each table. The same column name cannot be used as part of multiple column families.
Attachments
Issue Links
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- Closed
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