#16759: Expensive sql.Query cloning
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Reporter: Suor | Owner: Suor
Type: Bug | Status: new
Component: Database layer | Version: 1.3
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: orm performance | Needs documentation: 0
cloning | Patch needs improvement: 1
Has patch: 1 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Comment (by akaariai):
And now I remember what the strangeness was. Trees are created by starting
subtrees. When you start a subtree for tree node A, you modify the tree
inplace, such that references to A now point to the new subtree root, and
that subtree root has A in subtree_parents.
That API is really strange. You basically have some sort of global state
for the tree. You can not store a reference to a tree's root node. If
somebody, somewhere calls start_subtree() on the root node, you suddenly
have a reference to a new empty subtree of that root. The root node was
mutated inplace. The tree API is changed to something simpler and more
conventional in #17025. But changing the tree representation should not be
done for 1.4.
In short, the subtree_parents cloning in tree.clone() should be changed to
assert not self.subtree_parents. When cloning you must start from the real
tree root, and in that case no node in the tree should have
subtree_parents.
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Ticket URL: <https://code.djangoproject.com/ticket/16759#comment:22>
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