Alter table - access group modification after adding data

[Burak Cankurtaran]

Hi,

Within the ACCESS GROUP section of the CREATE TABLE HQL documentation,
the text describes that "access groups provide control over the
physical layout of the table data on disk". Does this mean that if the
ALTER TABLE hql command is used to add or modify an access group then
any existing data will also be rearranged. If so then it is wise to
have the access groups defined before the table is populated
extensively. Is this line of thought correct?

Thanks
Burak

[Doug Judd]

Currently you cannot move columns from one access group to another with ALTER TABLE.  We plan to support that in the future, but for now the access groups are fixed at table creation time.  ALTER TABLE does allow you to add access groups for new columns, however.

The benefit of access groups comes in situations where you have a table with, say, 100 columns and two of the columns are access together frequently.  By putting those two columns in their own access group, queries for those two columns are much more efficient because only the data for those two columns are read from disk to satisfy the query, instead of data for all 100 columns.

- Doug

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