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Add pg_partition_root to display top-most parent of a partition tree

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This is useful when looking at partition trees with multiple layers, and
combined with pg_partition_tree, it provides the possibility to show up
an entire tree by just knowing one member at any level.

Author: Michael Paquier
Reviewed-by: Álvaro Herrera, Amit Langote
Discussion: https://postgr.es/m/20181207014015.GP2407@paquier.xyz
This commit is contained in:
Michael Paquier
2019-02-08 08:56:14 +09:00
parent 34ea1ab7fd
commit 3677a0b26b
6 changed files with 153 additions and 11 deletions
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75
src/backend/utils/adt/partitionfuncs.c
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@@ -25,6 +25,33 @@
#include "utils/lsyscache.h"
#include "utils/syscache.h"
/*
* Checks if a given relation can be part of a partition tree. Returns
* false if the relation cannot be processed, in which case it is up to
* the caller to decide what to do, by either raising an error or doing
* something else.
*/
static bool
check_rel_can_be_partition(Oid relid)
{
char relkind;
/* Check if relation exists */
if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(relid)))
return false;
relkind = get_rel_relkind(relid);
/* Only allow relation types that can appear in partition trees. */
if (relkind != RELKIND_RELATION &&
relkind != RELKIND_FOREIGN_TABLE &&
relkind != RELKIND_INDEX &&
relkind != RELKIND_PARTITIONED_TABLE &&
relkind != RELKIND_PARTITIONED_INDEX)
return false;
return true;
}
/*
* pg_partition_tree
@@ -39,19 +66,10 @@ pg_partition_tree(PG_FUNCTION_ARGS)
{
#define PG_PARTITION_TREE_COLS 4
Oid rootrelid = PG_GETARG_OID(0);
char relkind = get_rel_relkind(rootrelid);
FuncCallContext *funcctx;
ListCell **next;
if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(rootrelid)))
PG_RETURN_NULL();
/* Return NULL for relation types that cannot appear in partition trees */
if (relkind != RELKIND_RELATION &&
relkind != RELKIND_FOREIGN_TABLE &&
relkind != RELKIND_INDEX &&
relkind != RELKIND_PARTITIONED_TABLE &&
relkind != RELKIND_PARTITIONED_INDEX)
if (!check_rel_can_be_partition(rootrelid))
PG_RETURN_NULL();
/* stuff done only on the first call of the function */
@@ -153,3 +171,40 @@ pg_partition_tree(PG_FUNCTION_ARGS)
/* done when there are no more elements left */
SRF_RETURN_DONE(funcctx);
}
/*
* pg_partition_root
*
* Returns the top-most parent of the partition tree to which a given
* relation belongs, or NULL if it's not (or cannot be) part of any
* partition tree.
*/
Datum
pg_partition_root(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
Oid rootrelid;
List *ancestors;
if (!check_rel_can_be_partition(relid))
PG_RETURN_NULL();
/*
* If the relation is not a partition (it may be the partition parent),
* return itself as a result.
*/
if (!get_rel_relispartition(relid))
PG_RETURN_OID(relid);
/* Fetch the top-most parent */
ancestors = get_partition_ancestors(relid);
rootrelid = llast_oid(ancestors);
list_free(ancestors);
/*
* "rootrelid" must contain a valid OID, given that the input relation is
* a valid partition tree member as checked above.
*/
Assert(OidIsValid(rootrelid));
PG_RETURN_OID(rootrelid);
}