#24203: Optimisation: adding multiple fields to same model should attempt to run
single ALTER TABLE statement
-------------------------------------+-------------------------------------
Reporter: peterlauri | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Migrations | Version: master
Severity: Normal | Resolution:
Keywords: migration | Triage Stage:
| Someday/Maybe
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by peterlauri):
Replying to [comment:2 timgraham]:
> Could you give some performance numbers for comparison?
I prepped a DB with some fields and 500k rows. The alter table statements
as in my original description executed each in few milliseconds. No
significant improvement to execute them in a single statement.
{{{
ballongen=# select count(*) from testtable;
count
--------
500000
(1 row)
Time: 34.261 ms
ballongen=# ALTER TABLE "testtable" ADD COLUMN "field2" varchar(100) NULL;
ALTER TABLE
Time: 56.649 ms
ballongen=# ALTER TABLE "testtable" ALTER COLUMN "field2" DROP DEFAULT;
ALTER TABLE
Time: 2.563 ms
ballongen=# ALTER TABLE "testtable" ADD COLUMN "field3" varchar(100) NULL;
ALTER TABLE
Time: 1.165 ms
ballongen=# ALTER TABLE "testtable" ALTER COLUMN "field3" DROP DEFAULT;
ALTER TABLE
Time: 0.240 ms
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/24203#comment:7>
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