PostgreSQL 19: The “repack” command

-- session 1
postgres=# create table t ( a int primary key, b text );
CREATE TABLE
postgres=# insert into t select i, md5(i::text) from generate_series(1,10000000) i;
INSERT 0 1000000
postgres=# vacuum full t;

-- session 2
postgres=# select count(*) from t;  -- this blocks until vacuum full completes

-- session 1
postgres=# \d t
                 Table "public.t"
 Column |  Type   | Collation | Nullable | Default 
--------+---------+-----------+----------+---------
 a      | integer |           | not null | 
 b      | text    |           |          | 
Indexes:
    "t_pkey" PRIMARY KEY, btree (a)

postgres=# cluster t using t_pkey;

-- session 2
postgres=# select count(*) from t;  -- this blocks until clustering completes

Introduce the REPACK command

REPACK absorbs the functionality of VACUUM FULL and CLUSTER in a single
command.  Because this functionality is completely different from
regular VACUUM, having it separate from VACUUM makes it easier for users
to understand; as for CLUSTER, the term is heavily overloaded in the
IT world and even in Postgres itself, so it's good that we can avoid it.

We retain those older commands, but de-emphasize them in the
documentation, in favor of REPACK; the difference between VACUUM FULL
and CLUSTER (namely, the fact that tuples are written in a specific
ordering) is neatly absorbed as two different modes of REPACK.

This allows us to introduce further functionality in the future that
works regardless of whether an ordering is being applied, such as (and
especially) a concurrent mode.

postgres=# \h repack
Command:     REPACK
Description: rewrite a table to reclaim disk space
Syntax:
REPACK [ ( option [, ...] ) ] [ table_and_columns [ USING INDEX [ index_name ] ] ]
REPACK [ ( option [, ...] ) ] USING INDEX

where option can be one of:

    VERBOSE [ boolean ]
    ANALYZE [ boolean ]
    CONCURRENTLY [ boolean ]

and table_and_columns is:

    table_name [ ( column_name [, ...] ) ]

URL: https://www.postgresql.org/docs/devel/sql-repack.html

-- session 1
postgres=# repack (concurrently) t;
-- or
postgres=# repack (concurrently) t using index t_pkey;

-- session 2
postgres=# select count(*) from t;  -- not blocking