[Django] #20516: Prepared statement for MySQL
Django
-------------------------------------+-------------------------------------
Reporter: est | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 1.6-alpha-1
(models, ORM) | Keywords: db, mysql, prepared
Severity: Normal | statement
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Hello,
Since we have persistant connection in Django 1.6 now, can we consider
adding prepared statements?
So we can create statements upon the first query, and use the prepared
statement for all the rest and so on.
http://dev.mysql.com/doc/refman/5.0/en/sql-syntax-prepared-statements.html
This could be a huge speed up for heavy db IO applications. Reduce
traffice size as well as RTT. Also improves security by parameterize
queries.
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Ticket URL: <https://code.djangoproject.com/ticket/20516>
Django <https://code.djangoproject.com/>
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Django
-------------------------------------+-------------------------------------
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Changes (by akaariai):
* needs_better_patch: => 0
* needs_tests: => 0
* version: 1.6-alpha-1 => master
* keywords: db, mysql, prepared statement => db, prepared statement
* needs_docs: => 0
* stage: Unreviewed => Accepted
Comment:
Yes, I think addition of prepared statements is something to consider. No
idea of what would be a nice API, or if this could be somehow delegated to
third party apps. The latter option means some hooks are needed somewhere
in the query execution path. One such point is execute_sql() where it
would be fairly straightforward to change the used SQL to prepared
statements if the query is set to use prepared statements.
FWIW there are use cases where prepared statements can give easily over
50% speedup. Such cases are simple to execute queries which retrieve just
a few rows of data, but which have a massive amount of joins (so that
planning overhead is big). Using .select_related() and complicated
.filter() clauses are easy ways to produce such queries.
I don't see any reason to restrict this to MySQL only.
(This feature seems to need at least these parts:
- API for setting given queryset to use prepared statements - using them
automatically is generally a bad idea
- Convert the query's execution to use prepared statement instead of
SQL. This consists of:
- A check if the given query is already prepared for the used
connection
- If so, use the correct prepared statement
- If not, create a new prepared statement and use that)
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:1>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
* cc: mpessas@… (added)
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Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:2>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by anonymous):
`with` statements seem to be the correct way to handle this from an API
standpoint.
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:3>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Comment (by FunkyBob):
Surely the security only improves if the DB driver is faulty? Django
already passes parameterised queries to the DB driver to handle escaping
[or pass through parameterised, as some do].
But in general, I'm happy to throw my brain behind this effort :)
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:4>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by FunkyBob):
One idea that struck me the other day-
A prepared statement could yield a function with keyword arguments
matching its bound parameters.
Something like:
s = MyModel.objects.filter(foo__bar=Param('able'),
baz=Param('baker')).exclude(foo_quux=7)
Though perhaps an explicit "prepare()" would be better, the Param
arguments mark where to bind parameters, and what to call them.
The, you can execute the query with:
for my in s(able=1, baker="wibble")
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:5>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Comment (by david@…):
This isn't just for MySQL. If possible, it would be really nice to have
some facility for using server-side prepare statements not created by
Django. https://github.com/dimitri/preprepare is an example of such a use
case
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:6>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Comment (by the_drow):
PostgresSQL also supports prepare statements.
@FunkyBob: That syntax looks great but the PreparedQuerySet object should
support a context manager.
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Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:7>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by FunkyBob):
Could you elaborate on how you see context manager working with this
feature?
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:8>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: db, prepared | Needs documentation: 0
statement | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Comment (by the_drow):
The way I see it a PreparedQuerySet should support the following:
* Preparing on execution of a query for the entire session:
{{{
qs = list(MyModel.objects.filter(foo__bar=1).prepare())
qs2 = list(MyModel.objects.filter(foo__bar=2)) # Already prepared for this
session (that is the connection)
}}}
The query parameters are inferred from the query itself.
This is very convenient and doesn't require anyone to learn the new
syntax.
* Preparing for a certain scope and deallocating:
{{{
with MyModel.objects.filter(foo__bar=Param('foobar')).prepare() as qs:
results = qs(1)
# Some logic
results = qs(2)
# Some logic
}}}
When the PreparedQuerySet enters the context the query is prepared. When
it exists the prepared query is deallocated.
It's not always a good idea to prepare queries for a very long time for
rapidly changing tables (small tables don't need to use indexes for
example).
* Preparing a query for usage in a Manager or QuerySet:
{{{
class MyQuerySet(QuerySet):
foobars = MyModel.objects.filter(foo__bar=Param('foobar')).prepare()
}}}
This will turn foobars into a callable with an argument named foobar.
The query will be prepared once the first query using it will be executed.
You can prepare ahead of time:
{{{
class MyQuerySet(QuerySet):
foobars =
MyModel.objects.filter(foo__bar=Param('foobar')).prepare(ahead=True) # I
need a better name for the argument here
}}}
You can also prepare a query that will be deallocated after a TTL:
{{{
class MyQuerySet(QuerySet):
foobars =
MyModel.objects.filter(foo__bar=Param('foobar')).prepare(ttl=60000)
}}}
Explicitly deallocating a prepared query should also be possible:
{{{
qs = MyModel.objects.filter(foo__bar=1).prepare()
results = list(qs)
qs2 = list(MyModel.objects.filter(foo__bar=2)) # Already prepared for this
session (that is the connection)
qs.deallocate()
results = list(qs) # the query is prepared again
}}}
The query will be prepared again once the first query is executed.
What do you guys think?
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:9>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: db, prepared | Triage Stage: Accepted
statement |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by thedrow):
I investigated about implementing it today and it turns out that the Query
class has a method called sql_with_params() which returns the SQL query
without concatenating the parameters.
MySQL uses the following syntax:
{{{#!sql
PREPARE usrrptplan FROM "SELECT * FROM users u, logs l WHERE u.usrid=? AND
u.usrid=l.usrid
AND l.date = ?;"
EXECUTE usrrptplan USING 1, NOW()
}}}
PostgreSQL uses the following syntax:
{{{#!sql
PREPARE usrrptplan (int) AS
SELECT * FROM users u, logs l WHERE u.usrid=$1 AND u.usrid=l.usrid
AND l.date = $2;
EXECUTE usrrptplan(1, NOW());
}}}
It seems that when you call prepare() you need to switch the query
entirely with the EXECUTE syntax.
Moreover, at least in PostgreSQL you have to check if the statement is
already prepared and there's no SQL syntax to do that.
You need to query the pg_prepared_statements table in order to verify that
it doesn't exist.
Since a prepared statement requires a name we can either randomize one or
have one provided for us.
I think that providing both options is a good idea.
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:10>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: db, prepared | Triage Stage: Accepted
statement |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by thedrow):
As apollo13 mentioned on IRC, prepared statements are at the session level
on PostgresSQL so we can just store them on the connection object.
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:11>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: db, prepared | Triage Stage: Accepted
statement |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by thedrow):
akaariai says we can just subclass the Query object and replace the
parameters with the prepared statements placeholders.
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:12>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: db, prepared | Triage Stage: Accepted
statement |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by shaib):
On Oracle, the concept of prepared statements is linked to a connection-
level statement cache. Prepared statements are not handled with different
SQL, but with different API calls -- specifically, cx_Oracle provides a
[http://cx-oracle.readthedocs.org/en/latest/cursor.html#Cursor.prepare
prepare] method on its cursors. This method is not currently used by
Django's Oracle backend.
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:13>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: db, prepared | Triage Stage: Accepted
statement |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: aron45 (added)
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:14>
Django
Reporter: est | Owner: nobody
Type: New feature | Status: new
(models, ORM) |
Severity: Normal | Resolution:
Keywords: db, prepared | Triage Stage: Accepted
statement |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: Jeongsoo, Park (added)
--
Ticket URL: <https://code.djangoproject.com/ticket/20516#comment:15>