#35918: SQLCompiler.execute_sql result_type CURSOR usage can be minimized
-------------------------------------+-------------------------------------
Reporter: Raphael Gaschignard | Owner: Raphael
Type: | Gaschignard
Cleanup/optimization | Status: assigned
Component: Database layer | Version: dev
(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
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Description changed by Raphael Gaschignard:
Old description:
> (This refactor is motivated by an ongoing experiment to integrate async
> cursor work into the ORM, by simplifying some cursor management)
>
> In ``django.cdb.models.sql.compiler.Compiler.execute_sql``, we can pass
> in the following result types: ``SINGLE``, ``MULTI``, ``NO_RESULTS``,
> and ``CURSOR``.
>
> ``execute_sql``'s docstring to that effect does not reflect this.
>
> - ``SINGLE`` returns a single row. It closes the cursor it uses to query.
> - ``MULTI`` returns many rows (wrapped in a cursor iterator). This either
> closes the cursor it uses to query, or returns an iterator that takes
> ownership of the cursor to close the cursor once reading of all the
> results are done.
> - ``NO_RESULTS`` returns nothing. It closes the cursor it uses to query.
> - ``CURSOR`` returns the cursor, without closing the cursor, effectively
> making the caller in charge of closing the cursor
>
> ``CURSOR`` returns an unclosed cursor that has to be manage by the
> caller. In practice, though, apart from a single test usage, Django's
> codebase currently only uses ``CURSOR`` to do one thing: get the number
> of rows, then close the cursor.
>
> To simplify cursor resource management, I have a two-pronged proposal:
> - a new result type, ``ROW_COUNT``, returns the rows and closes the
> cursor for you. This covers all non-test usage of ``CURSOR`` in Django
> currently.
> - ``CURSOR`` is renamed to ``LEAK_CURSOR``, as a way to more strongly
> indicate that you are now in charge of the cursor
>
> Main point here is to reduce the number of places an open cursor might
> come into play.
New description:
(This refactor is motivated by an ongoing experiment to integrate async
cursor work into the ORM, by simplifying some cursor management)
In `django.cdb.models.sql.compiler.Compiler.execute_sql`, we can pass in
the following result types: `SINGLE`, `MULTI`, `NO_RESULTS`, and
`CURSOR`.
`execute_sql`'s docstring to that effect does not reflect this.
- `SINGLE` returns a single row. It closes the cursor it uses to query.
- `MULTI` returns many rows (wrapped in a cursor iterator). This either
closes the cursor it uses to query, or returns an iterator that takes
ownership of the cursor to close the cursor once reading of all the
results are done.
- `NO_RESULTS` returns nothing. It closes the cursor it uses to query.
- `CURSOR` returns the cursor, without closing the cursor, effectively
making the caller in charge of closing the cursor
`CURSOR` returns an unclosed cursor that has to be manage by the caller.
In practice, though, apart from a single test usage, Django's codebase
currently only uses `CURSOR` to do one thing: get the number of rows, then
close the cursor.
To simplify cursor resource management, I have a two-pronged proposal:
- a new result type, `ROW_COUNT`, returns the rows and closes the cursor
for you. This covers all non-test usage of `CURSOR` in Django currently.
- `CURSOR` is renamed to `LEAK_CURSOR`, as a way to more strongly indicate
that you are now in charge of the cursor
Main point here is to reduce the number of places an open cursor might
come into play.
--
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Ticket URL: <https://code.djangoproject.com/ticket/35918#comment:1>
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