SYNC_WITH_HCATALOG_SCHEMA

Copies the structure of a Hive database schema available through the HCatalog Connector to a Vertica schema. If the HCatalog schema and the target Vertica schema have matching table names, SYNC_WITH_HCATALOG_SCHEMA overwrites the Vertica tables.

This function can synchronize the HCatalog schema directly. In this case, call it with the same schema name for the vertica_schema and hcatalog_schema parameters. The function can also synchronize a different schema to the HCatalog schema.

If you change the settings of HCatalog Connector configuration parameters, you must call this function again.

Syntax

SYNC_WITH_HCATALOG_SCHEMA( vertica_schema, hcatalog_schema, [drop_non_existent] )

Parameters

Privileges

Non-superuser: CREATE privileges on vertica_schema.

Users also require access to Hive data, one of the following:

• USAGE permissions on hcat_schema, if Hive does not use an authorization service to manage access.
• Permission through an authorization service (Sentry or Ranger), and access to the underlying files in HDFS. (Sentry can provide that access through ACL synchronization.)
• dbadmin user privileges, with or without an authorization service.

Data Type Matching

Hive STRING and BINARY data types are matched, in Vertica, to the VARCHAR(65000) and VARBINARY(65000) types. Adjust the data types with ALTER TABLE as needed after creating the schema. The maximum size of a VARCHAR or VARBINARY in Vertica is 65000, but you can use LONG VARCHAR and LONG VARBINARY to specify larger values.

Hive and Vertica define string length in different ways. In Hive the length is the number of characters; in Vertica it is the number of bytes. Thus, a character encoding that uses more than one byte, such as Unicode, can cause mismatches between the two. To avoid data truncation, set values in Vertica based on bytes, not characters.

If data size exceeds the column size, Vertica logs an event at read time in the QUERY_EVENTS system table.

Examples

The following example uses SYNC_WITH_HCATALOG_SCHEMA to synchronize an HCatalog schema named hcat:

=> CREATE HCATALOG SCHEMA hcat WITH hostname='hcathost' HCATALOG_SCHEMA='default' 
   HCATALOG_USER='hcatuser';
CREATE SCHEMA
=> SELECT sync_with_hcatalog_schema('hcat', 'hcat');
sync_with_hcatalog_schema                                             
----------------------------------------
Schema hcat synchronized with hcat
tables in hcat = 56
tables altered in hcat = 0
tables created in hcat = 56
stale tables in hcat = 0
table changes erred in hcat = 0
(1 row)

=> -- Use vsql's \d command to describe a table in the synced schema				
				
=> \d hcat.messages
List of Fields by Tables
  Schema   |   Table  | Column  |      Type      | Size  | Default | Not Null | Primary Key | Foreign Key
-----------+----------+---------+----------------+-------+---------+----------+-------------+-------------
hcat       | messages | id      | int            |     8 |         | f        | f           |
hcat       | messages | userid  | varchar(65000) | 65000 |         | f        | f           |
hcat       | messages | "time"  | varchar(65000) | 65000 |         | f        | f           |
hcat       | messages | message | varchar(65000) | 65000 |         | f        | f           |
(4 rows)

The following example uses SYNC_WITH_HCATALOG_SCHEMA followed by ALTER TABLE to adjust a column value:

=> CREATE HCATALOG SCHEMA hcat WITH hostname='hcathost' HCATALOG_SCHEMA='default' 
-> HCATALOG_USER='hcatuser';
CREATE SCHEMA
=> SELECT sync_with_hcatalog_schema('hcat', 'hcat');
...
=> ALTER TABLE hcat.t ALTER COLUMN a1 SET DATA TYPE long varchar(1000000);
=> ALTER TABLE hcat.t ALTER COLUMN a2 SET DATA TYPE long varbinary(1000000);

The following example uses SYNC_WITH_HCATALOG_SCHEMA with a local (non-HCatalog) schema:

=> CREATE HCATALOG SCHEMA hcat WITH hostname='hcathost' HCATALOG_SCHEMA='default'
-> HCATALOG_USER='hcatuser';
CREATE SCHEMA
=> CREATE SCHEMA hcat_local;
CREATE SCHEMA
=> SELECT sync_with_hcatalog_schema('hcat_local', 'hcat');