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There was no code to handle foreign key constraints on partitioned tables in the case of ALTER TABLE DETACH; and if you happened to ATTACH a partition that already had an equivalent constraint, that one was ignored and a new constraint was created. Adding this to the fact that foreign key cloning reuses the constraint name on the partition instead of generating a new name (as it probably should, to cater to SQL standard rules about constraint naming within schemas), the result was a pretty poor user experience -- the most visible failure was that just detaching a partition and re-attaching it failed with an error such as ERROR: duplicate key value violates unique constraint "pg_constraint_conrelid_contypid_conname_index" DETAIL: Key (conrelid, contypid, conname)=(26702, 0, test_result_asset_id_fkey) already exists. because it would try to create an identically-named constraint in the partition. To make matters worse, if you tried to drop the constraint in the now-independent partition, that would fail because the constraint was still seen as dependent on the constraint in its former parent partitioned table: ERROR: cannot drop inherited constraint "test_result_asset_id_fkey" of relation "test_result_cbsystem_0001_0050_monthly_2018_09" This fix attacks the problem from two angles: first, when the partition is detached, the constraint is also marked as independent, so the drop now works. Second, when the partition is re-attached, we scan existing constraints searching for one matching the FK in the parent, and if one exists, we link that one to the parent constraint. So we don't end up with a duplicate -- and better yet, we don't need to scan the referenced table to verify that the constraint holds. To implement this I made a small change to previously planner-only struct ForeignKeyCacheInfo to contain the constraint OID; also relcache now maintains the list of FKs for partitioned tables too. Backpatch to 11. Reported-by: Michael Vitale (bug #15425) Discussion: https://postgr.es/m/15425-2dbc9d2aa999f816@postgresql.org
src/backend/nodes/README
Node Structures
===============
Andrew Yu (11/94)
Introduction
------------
The current node structures are plain old C structures. "Inheritance" is
achieved by convention. No additional functions will be generated. Functions
that manipulate node structures reside in this directory.
FILES IN THIS DIRECTORY (src/backend/nodes/)
General-purpose node manipulation functions:
copyfuncs.c - copy a node tree
equalfuncs.c - compare two node trees
outfuncs.c - convert a node tree to text representation
readfuncs.c - convert text representation back to a node tree
makefuncs.c - creator functions for some common node types
nodeFuncs.c - some other general-purpose manipulation functions
Specialized manipulation functions:
bitmapset.c - Bitmapset support
list.c - generic list support
params.c - Param support
tidbitmap.c - TIDBitmap support
value.c - support for Value nodes
FILES IN src/include/nodes/
Node definitions:
nodes.h - define node tags (NodeTag)
primnodes.h - primitive nodes
parsenodes.h - parse tree nodes
plannodes.h - plan tree nodes
relation.h - planner internal nodes
execnodes.h - executor nodes
memnodes.h - memory nodes
pg_list.h - generic list
Steps to Add a Node
-------------------
Suppose you want to define a node Foo:
1. Add a tag (T_Foo) to the enum NodeTag in nodes.h. (If you insert the
tag in a way that moves the numbers associated with existing tags,
you'll need to recompile the whole tree after doing this. It doesn't
force initdb though, because the numbers never go to disk.)
2. Add the structure definition to the appropriate include/nodes/???.h file.
If you intend to inherit from, say a Plan node, put Plan as the first field
of your struct definition.
3. If you intend to use copyObject, equal, nodeToString or stringToNode,
add an appropriate function to copyfuncs.c, equalfuncs.c, outfuncs.c
and readfuncs.c accordingly. (Except for frequently used nodes, don't
bother writing a creator function in makefuncs.c) The header comments
in those files give general rules for whether you need to add support.
4. Add cases to the functions in nodeFuncs.c as needed. There are many
other places you'll probably also need to teach about your new node
type. Best bet is to grep for references to one or two similar existing
node types to find all the places to touch.
Historical Note
---------------
Prior to the current simple C structure definitions, the Node structures
used a pseudo-inheritance system which automatically generated creator and
accessor functions. Since every node inherited from LispValue, the whole thing
was a mess. Here's a little anecdote:
LispValue definition -- class used to support lisp structures
in C. This is here because we did not want to totally rewrite
planner and executor code which depended on lisp structures when
we ported postgres V1 from lisp to C. -cim 4/23/90