#24203: Optimisation: adding multiple fields to same model should attempt to run
single ALTER TABLE statement
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Reporter: peterlauri | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Migrations | Version: 1.7
Severity: Normal | Keywords: migration
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Origin: https://groups.google.com/d/msg/django-users/DDekrNgXH2U/k1un-
e8CbnMJ
When adding multiple fields to a Model the makemigrate and migrate does
not attempt to create one ALTER TABLE statement, but rather one per field
added. This can cause slow migrations of large tables.
I propose to optimise to attempt to merge multiple AddField to one single
ALTER TABLE request when the migrate is run.
My real world case the db backend was MySQL, here is PG example of 2nd
migration db output after adding two fields to one model.
{{{
Applying play.0002_auto_20150122_1825...DEBUG ALTER TABLE "play_play"
ADD COLUMN "field2" varchar(100) NULL; (params [])
DEBUG (0.000) ALTER TABLE "play_play" ADD COLUMN "field2" varchar(100)
NULL; args=[]
DEBUG ALTER TABLE "play_play" ALTER COLUMN "field2" DROP DEFAULT; (params
[])
DEBUG (0.000) ALTER TABLE "play_play" ALTER COLUMN "field2" DROP DEFAULT;
args=[]
DEBUG ALTER TABLE "play_play" ADD COLUMN "field3" varchar(100) NULL;
(params [])
DEBUG (0.000) ALTER TABLE "play_play" ADD COLUMN "field3" varchar(100)
NULL; args=[]
DEBUG ALTER TABLE "play_play" ALTER COLUMN "field3" DROP DEFAULT; (params
[])
DEBUG (0.000) ALTER TABLE "play_play" ALTER COLUMN "field3" DROP DEFAULT;
args=[]
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/24203>
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