database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-03 09:13:20 +03:00
Code Activity

ALTER TABLE ... DETACH PARTITION ... CONCURRENTLY

Browse Source 
Allow a partition be detached from its partitioned table without
blocking concurrent queries, by running in two transactions and only
requiring ShareUpdateExclusive in the partitioned table.

Because it runs in two transactions, it cannot be used in a transaction
block.  This is the main reason to use dedicated syntax: so that users
can choose to use the original mode if they need it.  But also, it
doesn't work when a default partition exists (because an exclusive lock
would still need to be obtained on it, in order to change its partition
constraint.)

In case the second transaction is cancelled or a crash occurs, there's
ALTER TABLE .. DETACH PARTITION .. FINALIZE, which executes the final
steps.

The main trick to make this work is the addition of column
pg_inherits.inhdetachpending, initially false; can only be set true in
the first part of this command.  Once that is committed, concurrent
transactions that use a PartitionDirectory will include or ignore
partitions so marked: in optimizer they are ignored if the row is marked
committed for the snapshot; in executor they are always included.  As a
result, and because of the way PartitionDirectory caches partition
descriptors, queries that were planned before the detach will see the
rows in the detached partition and queries that are planned after the
detach, won't.

A CHECK constraint is created that duplicates the partition constraint.
This is probably not strictly necessary, and some users will prefer to
remove it afterwards, but if the partition is re-attached to a
partitioned table, the constraint needn't be rechecked.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/20200803234854.GA24158@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2021-03-25 18:00:28 -03:00
parent 650d623530
commit 71f4c8c6f7
41 changed files with 2273 additions and 175 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
src/test/regress/sql/alter_table.sql
View File

@@ -2678,6 +2678,26 @@ DROP TABLE range_parted2;
SELECT * from part_rp;
DROP TABLE part_rp;
-- concurrent detach
CREATE TABLE range_parted2 (
a int
) PARTITION BY RANGE(a);
CREATE TABLE part_rp PARTITION OF range_parted2 FOR VALUES FROM (0) to (100);
BEGIN;
-- doesn't work in a partition block
ALTER TABLE range_parted2 DETACH PARTITION part_rp CONCURRENTLY;
COMMIT;
CREATE TABLE part_rpd PARTITION OF range_parted2 DEFAULT;
-- doesn't work if there's a default partition
ALTER TABLE range_parted2 DETACH PARTITION part_rp CONCURRENTLY;
-- doesn't work for the default partition
ALTER TABLE range_parted2 DETACH PARTITION part_rpd CONCURRENTLY;
DROP TABLE part_rpd;
-- works fine
ALTER TABLE range_parted2 DETACH PARTITION part_rp CONCURRENTLY;
\d+ range_parted2
DROP TABLE range_parted2;
-- Check ALTER TABLE commands for partitioned tables and partitions
-- cannot add/drop column to/from *only* the parent