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| author | Alvaro Herrera <alvherre@alvh.no-ip.org> | 2021-03-25 18:00:28 -0300 |
|---|---|---|
| committer | Alvaro Herrera <alvherre@alvh.no-ip.org> | 2021-03-25 18:00:28 -0300 |
| commit | 71f4c8c6f74ba021e55d35b1128d22fb8c6e1629 (patch) | |
| tree | c53d5e70ef2c8ec1723c9fb62fc8174ba6381e29 /src/backend/commands/indexcmds.c | |
| parent | 650d623530c884c087c565f1d3b8cd76f8fe2b95 (diff) | |
| download | postgresql-71f4c8c6f74ba021e55d35b1128d22fb8c6e1629.tar.gz postgresql-71f4c8c6f74ba021e55d35b1128d22fb8c6e1629.zip | |
ALTER TABLE ... DETACH PARTITION ... CONCURRENTLY
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
Diffstat (limited to 'src/backend/commands/indexcmds.c')
| -rw-r--r-- | src/backend/commands/indexcmds.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c index e4e1bbb7e00..166374cc0c9 100644 --- a/src/backend/commands/indexcmds.c +++ b/src/backend/commands/indexcmds.c @@ -410,7 +410,7 @@ CompareOpclassOptions(Datum *opts1, Datum *opts2, int natts) * GetCurrentVirtualXIDs. If, during any iteration, a particular vxid * doesn't show up in the output, we know we can forget about it. */ -static void +void WaitForOlderSnapshots(TransactionId limitXmin, bool progress) { int n_old_snapshots; @@ -1123,7 +1123,7 @@ DefineIndex(Oid relationId, */ if (partitioned && stmt->relation && !stmt->relation->inh) { - PartitionDesc pd = RelationGetPartitionDesc(rel); + PartitionDesc pd = RelationGetPartitionDesc(rel, false); if (pd->nparts != 0) flags |= INDEX_CREATE_INVALID; @@ -1180,7 +1180,7 @@ DefineIndex(Oid relationId, * * If we're called internally (no stmt->relation), recurse always. */ - partdesc = RelationGetPartitionDesc(rel); + partdesc = RelationGetPartitionDesc(rel, false); if ((!stmt->relation || stmt->relation->inh) && partdesc->nparts > 0) { int nparts = partdesc->nparts; |