29.5. Column Lists#
Each publication can optionally specify which columns of each table are replicated to subscribers. The table on the subscriber side must have at least all the columns that are published. If no column list is specified, then all columns on the publisher are replicated. SeeCREATE PUBLICATION for details on the syntax.
The choice of columns can be based on behavioral or performance reasons. However, do not rely on this feature for security: a malicious subscriber is able to obtain data from columns that are not specifically published. If security is a consideration, protections can be applied at the publisher side.
If no column list is specified, any columns added to the table later are automatically replicated. This means that having a column list which names all columns is not the same as having no column list at all.
A column list can contain only simple column references. The order of columns in the list is not preserved.
Specifying a column list when the publication also publishesFOR TABLES IN SCHEMA is not supported.
For partitioned tables, the publication parameterpublish_via_partition_root determines which column list is used. Ifpublish_via_partition_root istrue, the root partitioned table's column list is used. Otherwise, ifpublish_via_partition_root isfalse (the default), each partition's column list is used.
If a publication publishesUPDATE orDELETE operations, any column list must include the table's replica identity columns (seeREPLICA IDENTITY). If a publication publishes onlyINSERT operations, then the column list may omit replica identity columns.
Column lists have no effect for theTRUNCATE command.
During initial data synchronization, only the published columns are copied. However, if the subscriber is from a release prior to 15, then all the columns in the table are copied during initial data synchronization, ignoring any column lists.
Warning: Combining Column Lists from Multiple Publications
There's currently no support for subscriptions comprising several publications where the same table has been published with different column lists.CREATE SUBSCRIPTION disallows creating such subscriptions, but it is still possible to get into that situation by adding or altering column lists on the publication side after a subscription has been created.
This means changing the column lists of tables on publications that are already subscribed could lead to errors being thrown on the subscriber side.
If a subscription is affected by this problem, the only way to resume replication is to adjust one of the column lists on the publication side so that they all match; and then either recreate the subscription, or useALTER SUBSCRIPTION ... DROP PUBLICATION to remove one of the offending publications and add it again.
29.5.1. Examples#
Create a tablet1 to be used in the following example.
test_pub=# CREATE TABLE t1(id int, a text, b text, c text, d text, e text, PRIMARY KEY(id));CREATE TABLE
Create a publicationp1. A column list is defined for tablet1 to reduce the number of columns that will be replicated. Notice that the order of column names in the column list does not matter.
test_pub=# CREATE PUBLICATION p1 FOR TABLE t1 (id, b, a, d);CREATE PUBLICATION
psql can be used to show the column lists (if defined) for each publication.
test_pub=# \dRp+ Publication p1 Owner | All tables | Inserts | Updates | Deletes | Truncates | Via root----------+------------+---------+---------+---------+-----------+---------- postgres | f | t | t | t | t | fTables: "public.t1" (id, a, b, d)
psql can be used to show the column lists (if defined) for each table.
test_pub=# \d t1 Table "public.t1" Column | Type | Collation | Nullable | Default--------+---------+-----------+----------+--------- id | integer | | not null | a | text | | | b | text | | | c | text | | | d | text | | | e | text | | |Indexes: "t1_pkey" PRIMARY KEY, btree (id)Publications: "p1" (id, a, b, d)
On the subscriber node, create a tablet1 which now only needs a subset of the columns that were on the publisher tablet1, and also create the subscriptions1 that subscribes to the publicationp1.
test_sub=# CREATE TABLE t1(id int, b text, a text, d text, PRIMARY KEY(id));CREATE TABLEtest_sub=# CREATE SUBSCRIPTION s1test_sub-# CONNECTION 'host=localhost dbname=test_pub application_name=s1'test_sub-# PUBLICATION p1;CREATE SUBSCRIPTION
On the publisher node, insert some rows to tablet1.
test_pub=# INSERT INTO t1 VALUES(1, 'a-1', 'b-1', 'c-1', 'd-1', 'e-1');INSERT 0 1test_pub=# INSERT INTO t1 VALUES(2, 'a-2', 'b-2', 'c-2', 'd-2', 'e-2');INSERT 0 1test_pub=# INSERT INTO t1 VALUES(3, 'a-3', 'b-3', 'c-3', 'd-3', 'e-3');INSERT 0 1test_pub=# SELECT * FROM t1 ORDER BY id; id | a | b | c | d | e----+-----+-----+-----+-----+----- 1 | a-1 | b-1 | c-1 | d-1 | e-1 2 | a-2 | b-2 | c-2 | d-2 | e-2 3 | a-3 | b-3 | c-3 | d-3 | e-3(3 rows)
Only data from the column list of publicationp1 is replicated.
test_sub=# SELECT * FROM t1 ORDER BY id; id | b | a | d----+-----+-----+----- 1 | b-1 | a-1 | d-1 2 | b-2 | a-2 | d-2 3 | b-3 | a-3 | d-3(3 rows)