[Pig Wiki] Update of "Howl/HowlAuthorizationProposal" by PradeepKamath

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The "Howl/HowlAuthorizationProposal" page has been changed by PradeepKamath.
http://wiki.apache.org/pig/Howl/HowlAuthorizationProposal

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New page:
<<TableOfContents>>

<<Anchor(Permissions)>>
== Permissions ==
The initial idea for authorization in Howl is to use the hdfs permissions to authorize metadata operations. To be able to do this, we would like to extend createTable() to add the ability to record a different group from the user's primary group and to record the complete unix permissions on the table directory. Also, we would like to have a way for partition directories to inherit permissions and group information based on the table directory. To keep the metastore backward compatible for use with hive. The following conf variables can be used to achieve these objectives:
   * table.group.name : value will indicate the name of the unix group for the table directory. This will be used by createTable() to perform a chgrp to the value provided. This property will provide the user the ability to choose from one of the many unix groups he is part of to associate with the table.
   * table.permissions : value will be of the form rwxrwxrwx to indicate read-write-execute permissions on the table directory. This will be used by createTable() to perform a chmod to the value provided. This will let the user decide what permissions he wants on the table.
   * partitions.inherit.permissions : a value of true will indicate that partitions inherit the group name and permissions of the table level directory. This will be used by addPartition() to perform a chgrp and chmod to the values as on the table directory.

Conf properties are preferable over API changes since the complete authorization design for hive is not finalized yet. These properties can be deprecated/removed when that is in place. These properties would also be useful to some installation of vanilla hive since at least DFS level authorization can now be achieved by hive without the user having to manually perform chgrp and chmod operations on DFS.

<<Anchor(Reading_data(Select)/Writing_data_(Insert))>>
== Reading data(Select)/Writing data (Insert) ==
This will simply be governed by the dfs permission at the time of the read and will result in runtime errors if the user does not have permissions.

<<Anchor(Create_table)>>
== Create table ==

<<Anchor(Internal/External_table_without_location_specified)>>
=== Internal/External table without location specified ===
If the user has permissions to the directory pointed by hive.metastore.warehouse.dir then he can create the table. 

<<Anchor(Internal/External_table_with_location_specified)>>
=== Internal/External table with location specified ===
If the user has permissions to the location specified then he can create the table.

<<Anchor(Drop_Table)>>
== Drop Table ==
A user can drop a table (internal or external) only if he has write permissions to the table directory. A user could have write permission either by virtue of him being the owner of the table or through the group he belongs
to. So if the permissions on the table directory allow him to write to it, he can drop the table.

<<Anchor(Partition_permissions)>>
== Partition permissions ==
Partition directories will inherit the permissions/(owner,group) of the table directory.

<<Anchor(Alter_table)>>
== Alter table ==
A user can "alter" table if he has write permissions on the table directory. So any of the following alter table commands are allowed only if the user has write permissions on the table directory:
   * ALTER TABLE table_name ADD partition_spec [ LOCATION 'location1' ] partition_spec [ LOCATION 'location2' ] ...
   * ALTER TABLE table_name DROP partition_spec, partition_spec,...
   * ALTER TABLE table_name RENAME TO new_table_name
   * ALTER TABLE table_name CHANGE [COLUMN] col_old_name col_new_name column_type [COMMENT col_comment] [FIRST||AFTER column_name]
   * ALTER TABLE table_name ADD||REPLACE COLUMNS (col_name data_type [COMMENT col_comment], ...)
   * ALTER TABLE table_name SET TBLPROPERTIES table_properties
   * ALTER TABLE table_name SET SERDE serde_class_name [WITH SERDEPROPERTIES serde_properties]
   * ALTER TABLE table_name SET SERDEPROPERTIES serde_properties
   * ALTER TABLE table_name SET FILEFORMAT file_format
   * ALTER TABLE table_name CLUSTERED BY (col_name, col_name, ...) [SORTED BY (col_name, ...)] INTO num_buckets BUCKETS
   * ALTER TABLE table_name TOUCH;
   * ALTER TABLE table_name TOUCH PARTITION partition_spec;

<<Anchor(Show_tables)>>
== Show tables ==
Since the top level warehouse dir will have read/write permissions for everyone, show tables will show all tables to all users 

<<Anchor(Show_Table/Partitions_Extended)>>
== Show Table/Partitions Extended ==
A user can issue "show table/partitions extended" on a table only if he has read permissions on the table directory. This query is of the form:
   * SHOW TABLE EXTENDED [IN||FROM database_name] LIKE identifier_with_wildcards [PARTITION(partition_desc)]

<<Anchor(Show_partitions)>>
== Show partitions ==
A user can issue "show partitions" on a table only if he has read permissions on the table directory.

<<Anchor(Describe_table/column/partition)>>
== Describe table/column/partition ==
A user can issue "describe table/column/partition" on a table only if he has read permissions on the table directory.

<<Anchor(Database_related_operations)>>
== Database related operations ==

<<Anchor(create_db)>>
=== create db ===
Just like create table, create db will have db.group.name and db.permissions properties which will dictate the group and permissions of the db directory. This will be set up by the howl cli and the database directory will need to be updated with the appropriate chgroup and chmod operations. There will be '''NO''' inheritance of permissions from db directory to table directory. The table directory can have potentially different group/perms from the db directory.

<<Anchor(use_db)>>
=== use db ===
use db will be permitted only if the user has read permission on the db directory. So subsequent operation like create table will still be authorized based on the rules laid above once the "use db" call has been authorized. So the user would need write permission on the db directory to be able create the table directory under it.

If  db.tablename syntax is supported (I believe it may not be supported in the initial commit), then create db.tablename will need to check that the user has write permission on db directory.