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psql

ALTER TABLE

Alter an existing table.

Table of contents

Synopsis

ALTER [ BLOB ] TABLE { ONLY table_ident
                       | table_ident [ PARTITION (partition_column = value [ , ... ]) ] }
  { SET ( parameter = value [ , ... ] )
    | RESET ( parameter [ , ... ] )
    | ADD [ COLUMN ] column_name data_type [ column_constraint [ ... ] ]
    | OPEN
    | CLOSE
    | RENAME TO table_ident
    | REROUTE reroute_option
  }

where column_constraint is:

{ PRIMARY KEY |
  NOT NULL |
  INDEX { OFF | USING { PLAIN |
                        FULLTEXT [ WITH ( analyzer = analyzer_name ) ]  } |
  [ CONSTRAINT check_constraint_name ] CHECK (boolean_expression)
}

Description

ALTER TABLE can be used to modify an existing table definition. It provides options to add columns, modify constraints, enabling or disabling table parameters and allows to execute a shard reroute allocation.

Use the BLOB keyword in order to alter a blob table (see blob_support). Blob tables cannot have custom columns which means that the ADD COLUMN keyword won't work.

While altering a partitioned table, using ONLY will apply changes for the table only and not for any possible existing partitions. So these changes will only be applied to new partitions. The ONLY keyword cannot be used together with a PARTITION clause.

See the CREATE TABLE with_clause for a list of available parameters.

table_ident

The name (optionally schema-qualified) of the table to alter.

Clauses

PARTITION

If the table is partitioned this clause can be used to alter only a single partition.

Note

BLOB tables cannot be partitioned and hence this clause cannot be used.

This clause identifies a single partition. It takes one or more partition columns with a value each to identify the partition to alter.

[ PARTITION ( partition_column = value [ , ... ] ) ]
partition_column

The name of the column by which the table is partitioned.

All partition columns that were part of the partitioned_by_clause of the ref-create-table statement must be specified.

value

The columns value.

Alter Partitioned Tables <partitioned_tables_alter>

Arguments

SET/RESET

Can be used to change a table parameter to a different value. Using RESET will reset the parameter to its default value.

parameter

The name of the parameter that is set to a new value or its default.

The supported parameters are listed in the CREATE TABLE WITH CLAUSE <with_clause> documentation. In addition to those, for dynamically changing the number of allocated shards, the parameter number_of_shards can be used. For more more info on that, see alter_change_number_of_shard.

ADD COLUMN

Can be used to add an additional column to a table. While columns can be added at any time, adding a new generated column <ref-generated-columns> is only possible if the table is empty. In addition, adding a base column with ref-default-clause is not supported. It is possible to define a CHECK constraint with the restriction that only the column being added may be used in the boolean expression.

data_type

Data type of the column which should be added.

column_name

Name of the column which should be added.

OPEN/CLOSE

Can be used to open or close the table, respectively. Closing a table prevents all operations, except ALTER TABLE ... OPEN, to fail. Operations on closed partitions will not produce an exception, but will have no effect. Similarly, like SELECT and INSERT on partitioned will exclude closed partitions and continue working.

RENAME TO

Can be used to rename a table, while maintaining its schema and data. During this operation the shards of the table will become temporarily unavailable.

REROUTE

The REROUTE command provides various options to manually control the allocation of shards. It allows the enforcement of explicit allocations, cancellations and the moving of shards between nodes in a cluster. See ddl_reroute_shards to get the convenient use-cases.

The rowcount defines if the reroute or allocation process of a shard was acknowledged or rejected.

Note

Partitioned tables require a Partition Clause <ref-alter-table-partition-clause> in order to specify a unique shard_id.

[ REROUTE reroute_option]

where reroute_option is:

{ MOVE SHARD shard_id FROM node TO node
  | ALLOCATE REPLICA SHARD shard_id ON node
  | PROMOTE REPLICA SHARD shard_id ON node [ WITH (accept_data_loss = { TRUE | FALSE }) ]
  | CANCEL SHARD shard_id ON node [ WITH (allow_primary = {TRUE|FALSE}) ]
}
shard_id

The shard id. Ranges from 0 up to the specified number of sys-shards shards of a table.

node

The ID or name of a node within the cluster.

See sys-nodes how to gain the unique ID.

REROUTE supports the following options to start/stop shard allocation:

MOVE

A started shard gets moved from one node to another. It requests a table_ident and a shard_id to identify the shard that receives the new allocation. Specify FROM node for the node to move the shard from and TO node to move the shard to.

ALLOCATE REPLICA

Allows to force allocation of an unassigned replica shard on a specific node.

PROMOTE REPLICA

Force promote a stale replica shard to a primary. In case a node holding a primary copy of a shard had a failure and the replica shards are out of sync, the system won't promote the replica to primary automatically, as it would result in a silent data loss.

Ideally the node holding the primary copy of the shard would be brought back into the cluster, but if that is not possible due to a permanent system failure, it is possible to accept the potential data loss and force promote a stale replica using this command.

The parameter accept_data_loss needs to be set to true in order for this command to work. If it is not provided or set to false, the command will error out.

CANCEL

This cancels the allocation/recovery of a shard_id of a table_ident on a given node. The allow_primary flag indicates if it is allowed to cancel the allocation of a primary shard.