Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:
 Type:   |  AllenJonathan
  Cleanup/optimization   |   Status:  closed
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  fixed
 Keywords:   | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak ):

 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 In [changeset:"1058fc7023d04d07c22a5e667b6a446705119b14" 1058fc70]:
 {{{
 #!CommitTicketReference repository=""
 revision="1058fc7023d04d07c22a5e667b6a446705119b14"
 Fixed #33191 -- Avoided clearing cached reference when saving child after
 parent.

 Thanks Barry Johnson for the report.
 }}}

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:
 Type:   |  AllenJonathan
  Cleanup/optimization   |   Status:  assigned
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Ready for
 |  checkin
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak):

 * stage:  Accepted => Ready for checkin


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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:
 Type:   |  AllenJonathan
  Cleanup/optimization   |   Status:  assigned
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  1|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Mariusz Felisiak):

 * owner:  nobody => AllenJonathan
 * status:  new => assigned
 * has_patch:  0 => 1


Comment:

 [https://github.com/django/django/pull/15737 PR]

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  Vishal
 Type:   |  Pandey
  Cleanup/optimization   |   Status:  assigned
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Vishal Pandey):

 * owner:  nobody => Vishal Pandey
 * status:  new => assigned


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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Mariusz Felisiak):

 Replying to [comment:7 Barry Johnson]:
 > Changed the suggested correction based on the discussion within the
 mailing list.

 Would you like to prepare a patch?

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Barry Johnson):

 Changed the suggested correction based on the discussion within the
 mailing list.

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Description changed by Barry Johnson:

Old description:

> Consider this case of ORM models "Parent" and "Child", where Child has a
> foreign key reference to Parent (and the database can return generated
> IDs following insert operations):
>
> {{{
> parent = Parent(name='parent_object')
> child = Child(parent=parent)
> parent.save()
> child.save()
> print(child.parent.name)
> }}}
>
> The print statement will cause an unnecessary lazy read of the parent
> object.
>
> In the application where this behavior was first observed, the
> application was creating thousands of parent and child objects using
> bulk_create().  The subsequent lazy reads occurred when creating log
> entries to record the action, and added thousands of unwanted SELECT
> queries.
>
> Closed ticket #29497 solved a problem with potential data loss in this
> situation by essentially executing {{{child.parent_id =
> child.parent.pk}}} while preparing the child object to be saved.
> However, when the child's ForeignKeyDeferredAttrbute "parent_id" changes
> value from None to the parent's ID, the child's internal cache containing
> the reference to "parent" is cleared.  The subsequent reference to
> child.parent then must do a lazy read and reload parent from the
> database.
>
> A workaround to avoid this lazy read is to explicitly update both the
> "parent_id" and "parent" cache entry by adding this non-intuitive
> statement:
> {{{child.parent = child.parent}}}
> after executing parent.save()
>
> But it appears that a simple change could avoid clearing the cache in
> this narrow case.
> Within Model._prepare_related_fields_for_save(), replace
> {{{setattr(self, field.attname, obj.pk)}}}
> with
> {{{self.__dict__[field.attname] = obj.pk}}}
>
> This suggested code has -not- been tested.
>
> This change would set the associated "parent_id" attribute to the desired
> value without affecting the cache.  In this spot of the code, "obj" is
> currently set to the cached parent object that we want to preserve, and
> we're just reconciling the associated copy of the parent's primary key.

New description:

 Consider this case of ORM models "Parent" and "Child", where Child has a
 foreign key reference to Parent (and the database can return generated IDs
 following insert operations):

 {{{
 parent = Parent(name='parent_object')
 child = Child(parent=parent)
 parent.save()
 child.save()
 print(child.parent.name)
 }}}

 The print statement will cause an unnecessary lazy read of the parent
 object.

 In the application where this behavior was first observed, the application
 was creating thousands of parent and child objects using bulk_create().
 The subsequent lazy reads occurred when creating log entries to record the
 action, and added thousands of unwanted SELECT queries.

 Closed ticket #29497 solved a problem with potential data loss in this
 situation by essentially executing {{{child.parent_id = child.parent.pk}}}
 while preparing the child object to be saved.  However, when the child's
 ForeignKeyDeferredAttrbute "parent_id" changes value from None to the
 parent's ID, the child's internal cache containing the reference to
 "parent" is cleared.  The subsequent reference to child.parent then must
 do a lazy read and reload parent from the database.

 A workaround to avoid this lazy read is to explicitly update both the
 "parent_id" and "parent" cache entry by adding this non-intuitive
 statement:
 {{{child.parent = child.parent}}}
 after executing parent.save()

 But it appears that a simple change could avoid clearing the cache in this
 narrow case.
 Within Model._prepare_related_fields_for_save(), replace
 {{{setattr(self, field.attname, obj.pk)}}}
 with
 {{{setattr(self, field.name, obj)}}}

 This suggested code has -not- been tested.

 This change would set the associated "parent_id" attribute while ensuring
 that the currently referenced object remains referenced.

--

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by John Speno):

 * cc: John Speno (added)


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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:  Accepted
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Carlton Gibson):

 * status:  closed => new
 * resolution:  wontfix =>
 * stage:  Unreviewed => Accepted


Comment:

 [https://groups.google.com/g/django-
 developers/c/JNCrmmSAU5Y/m/7NFUx9eTAAAJ Follow up discussion on the
 mailing list].
 Reopening based on the discussion there.

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  closed
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Carlton Gibson):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 Hi Barry. Thanks for the report.

 For me, this is just how things are expected to work, so I'm going to say
 wontfix. I'm happy if you want to take it to the DevelopersMailingList for
 a wider discussion, but (in general) I'm suspicious of a ''"simple
 change"'' adjusting a long-standing behaviour like this… (Perhaps there's
 a case to be made on the mailing list though.)

 To address the example, my first thought is that you should be saving
 `parent` before creating child:

 {{{
 parent = Parent(name='parent_object')
 parent.save()
 child = Child(parent=parent)
 ...
 }}}

 My second is that, you have `parent`, so print the name from there:

 {{{
 print(parent.name)
 }}}

 I appreciate you've no-doubt reduced this in order to show the issue more
 clearly than in a real example, but I'd suspect those thoughts would go
 back to the more realistic case.

 However, as I say, the DevelopersMailingList is a better venue to pursue
 this kind of thing.
 Thanks.

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Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Description changed by Carlton Gibson:

Old description:

> Consider this case of ORM models "Parent" and "Child", where Child has a
> foreign key reference to Parent (and the database can return generated
> IDs following insert operations):
>
> {{{
> parent = Parent(name='parent_object')
> child = Child(parent=parent)
> parent.save()
> child.save()
> print(child.parent.name)
> }}}
>
> The print statement will cause an unnecessary lazy read of the parent
> object.
>
> In the application where this behavior was first observed, the
> application was creating thousands of parent and child objects using
> bulk_create().  The subsequent lazy reads occurred when creating log
> entries to record the action, and added thousands of unwanted SELECT
> queries.
>
> Closed ticket 29497 solved a problem with potential data loss in this
> situation by essentially executing {{{child.parent_id =
> child.parent.pk}}} while preparing the child object to be saved.
> However, when the child's ForeignKeyDeferredAttrbute "parent_id" changes
> value from None to the parent's ID, the child's internal cache containing
> the reference to "parent" is cleared.  The subsequent reference to
> child.parent then must do a lazy read and reload parent from the
> database.
>
> A workaround to avoid this lazy read is to explicitly update both the
> "parent_id" and "parent" cache entry by adding this non-intuitive
> statement:
> {{{child.parent = child.parent}}}
> after executing parent.save()
>
> But it appears that a simple change could avoid clearing the cache in
> this narrow case.
> Within Model._prepare_related_fields_for_save(), replace
> {{{setattr(self, field.attname, obj.pk)}}}
> with
> {{{self.__dict__[field.attname] = obj.pk}}}
>
> This suggested code has -not- been tested.
>
> This change would set the associated "parent_id" attribute to the desired
> value without affecting the cache.  In this spot of the code, "obj" is
> currently set to the cached parent object that we want to preserve, and
> we're just reconciling the associated copy of the parent's primary key.

New description:

 Consider this case of ORM models "Parent" and "Child", where Child has a
 foreign key reference to Parent (and the database can return generated IDs
 following insert operations):

 {{{
 parent = Parent(name='parent_object')
 child = Child(parent=parent)
 parent.save()
 child.save()
 print(child.parent.name)
 }}}

 The print statement will cause an unnecessary lazy read of the parent
 object.

 In the application where this behavior was first observed, the application
 was creating thousands of parent and child objects using bulk_create().
 The subsequent lazy reads occurred when creating log entries to record the
 action, and added thousands of unwanted SELECT queries.

 Closed ticket #29497 solved a problem with potential data loss in this
 situation by essentially executing {{{child.parent_id = child.parent.pk}}}
 while preparing the child object to be saved.  However, when the child's
 ForeignKeyDeferredAttrbute "parent_id" changes value from None to the
 parent's ID, the child's internal cache containing the reference to
 "parent" is cleared.  The subsequent reference to child.parent then must
 do a lazy read and reload parent from the database.

 A workaround to avoid this lazy read is to explicitly update both the
 "parent_id" and "parent" cache entry by adding this non-intuitive
 statement:
 {{{child.parent = child.parent}}}
 after executing parent.save()

 But it appears that a simple change could avoid clearing the cache in this
 narrow case.
 Within Model._prepare_related_fields_for_save(), replace
 {{{setattr(self, field.attname, obj.pk)}}}
 with
 {{{self.__dict__[field.attname] = obj.pk}}}

 This suggested code has -not- been tested.

 This change would set the associated "parent_id" attribute to the desired
 value without affecting the cache.  In this spot of the code, "obj" is
 currently set to the cached parent object that we want to preserve, and
 we're just reconciling the associated copy of the parent's primary key.

--

-- 
Ticket URL: 

Re: [Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
 Reporter:  Barry Johnson|Owner:  nobody
 Type:   |   Status:  new
  Cleanup/optimization   |
Component:  Database layer   |  Version:  3.2
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:   | Triage Stage:
 |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Description changed by Barry Johnson:

Old description:

> Consider this case of ORM models "Parent" and "Child", where Child has a
> foreign key reference to Parent (and the database can return generated
> IDs following insert operations):
>
> {{{
> parent = Parent(name='parent_object')
> child = child(parent=parent)
> parent.save()
> child.save()
> print(child.parent.name)
> }}}
>
> The print statement will cause an unnecessary lazy read of the parent
> object.
>
> In the application where this behavior was first observed, the
> application was creating thousands of parent and child objects using
> bulk_create().  The subsequent lazy reads occurred when creating log
> entries to record the action, and added thousands of unwanted SELECT
> queries.
>
> Closed ticket 29497 solved a problem with potential data loss in this
> situation by essentially executing {{{child.parent_id =
> child.parent.pk}}} while preparing the child object to be saved.
> However, when the child's ForeignKeyDeferredAttrbute "parent_id" changes
> value from None to the parent's ID, the child's internal cache containing
> the reference to "parent" is cleared.  The subsequent reference to
> child.parent then must do a lazy read and reload parent from the
> database.
>
> A workaround to avoid this lazy read is to explicitly update both the
> "parent_id" and "parent" cache entry by adding this non-intuitive
> statement:
> {{{child.parent = child.parent}}}
> after executing parent.save()
>
> But it appears that a simple change could avoid clearing the cache in
> this narrow case.
> Within Model._prepare_related_fields_for_save(), replace
> {{{setattr(self, field.attname, obj.pk)}}}
> with
> {{{self.__dict__[field.attname] = obj.pk}}}
>
> This suggested code has -not- been tested.
>
> This change would set the associated "parent_id" attribute to the desired
> value without affecting the cache.  In this spot of the code, "obj" is
> currently set to the cached parent object that we want to preserve, and
> we're just reconciling the associated copy of the parent's primary key.

New description:

 Consider this case of ORM models "Parent" and "Child", where Child has a
 foreign key reference to Parent (and the database can return generated IDs
 following insert operations):

 {{{
 parent = Parent(name='parent_object')
 child = Child(parent=parent)
 parent.save()
 child.save()
 print(child.parent.name)
 }}}

 The print statement will cause an unnecessary lazy read of the parent
 object.

 In the application where this behavior was first observed, the application
 was creating thousands of parent and child objects using bulk_create().
 The subsequent lazy reads occurred when creating log entries to record the
 action, and added thousands of unwanted SELECT queries.

 Closed ticket 29497 solved a problem with potential data loss in this
 situation by essentially executing {{{child.parent_id = child.parent.pk}}}
 while preparing the child object to be saved.  However, when the child's
 ForeignKeyDeferredAttrbute "parent_id" changes value from None to the
 parent's ID, the child's internal cache containing the reference to
 "parent" is cleared.  The subsequent reference to child.parent then must
 do a lazy read and reload parent from the database.

 A workaround to avoid this lazy read is to explicitly update both the
 "parent_id" and "parent" cache entry by adding this non-intuitive
 statement:
 {{{child.parent = child.parent}}}
 after executing parent.save()

 But it appears that a simple change could avoid clearing the cache in this
 narrow case.
 Within Model._prepare_related_fields_for_save(), replace
 {{{setattr(self, field.attname, obj.pk)}}}
 with
 {{{self.__dict__[field.attname] = obj.pk}}}

 This suggested code has -not- been tested.

 This change would set the associated "parent_id" attribute to the desired
 value without affecting the cache.  In this spot of the code, "obj" is
 currently set to the cached parent object that we want to preserve, and
 we're just reconciling the associated copy of the parent's primary key.

--

-- 
Ticket URL: 

[Django] #33191: Avoid unnecessary clear of cached reference

[Django]

#33191: Avoid unnecessary clear of cached reference
-+-
   Reporter: |  Owner:  nobody
  callerbear |
   Type: | Status:  new
  Cleanup/optimization   |
  Component:  Database   |Version:  3.2
  layer (models, ORM)|
   Severity:  Normal |   Keywords:
   Triage Stage: |  Has patch:  0
  Unreviewed |
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  0
  UI/UX:  0  |
-+-
 Consider this case of ORM models "Parent" and "Child", where Child has a
 foreign key reference to Parent (and the database can return generated IDs
 following insert operations):

 {{{
 parent = Parent(name='parent_object')
 child = child(parent=parent)
 parent.save()
 child.save()
 print(child.parent.name)
 }}}

 The print statement will cause an unnecessary lazy read of the parent
 object.

 In the application where this behavior was first observed, the application
 was creating thousands of parent and child objects using bulk_create().
 The subsequent lazy reads occurred when creating log entries to record the
 action, and added thousands of unwanted SELECT queries.

 Closed ticket 29497 solved a problem with potential data loss in this
 situation by essentially executing {{{child.parent_id = child.parent.pk}}}
 while preparing the child object to be saved.  However, when the child's
 ForeignKeyDeferredAttrbute "parent_id" changes value from None to the
 parent's ID, the child's internal cache containing the reference to
 "parent" is cleared.  The subsequent reference to child.parent then must
 do a lazy read and reload parent from the database.

 A workaround to avoid this lazy read is to explicitly update both the
 "parent_id" and "parent" cache entry by adding this non-intuitive
 statement:
 {{{child.parent = child.parent}}}
 after executing parent.save()

 But it appears that a simple change could avoid clearing the cache in this
 narrow case.
 Within Model._prepare_related_fields_for_save(), replace
 {{{setattr(self, field.attname, obj.pk)}}}
 with
 {{{self.__dict__[field.attname] = obj.pk}}}

 This suggested code has -not- been tested.

 This change would set the associated "parent_id" attribute to the desired
 value without affecting the cache.  In this spot of the code, "obj" is
 currently set to the cached parent object that we want to preserve, and
 we're just reconciling the associated copy of the parent's primary key.

-- 
Ticket URL: 
Django 
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