hi,
in certain cases, django-postgresql creates duplicate indexes...
imagine the following model:
> class Item(Model):
> text = CharField(maxlength=200,unique=True, db_index = True)
when installing it, it generates the following sql: (manage.py sqlall)
> BEGIN;
> CREATE TABLE "y_item" (
> "id" serial NOT NULL PRIMARY KEY,
> "text" varchar(200) NOT NULL UNIQUE
> );
> CREATE UNIQUE INDEX y_item_text ON "y_item" ("text");
> COMMIT;
and the result is the following db schema:
> boo=# \d y_item
> Table "public.y_item"
> Column | Type | Modifiers
>
> --------+------------------------+-----------------------------------------------------
> id | integer | not null default
> nextval('y_item_id_seq'::regclass)
> text | character varying(200) | not null
> Indexes:
> "y_item_pkey" PRIMARY KEY, btree (id)
> "y_item_text" UNIQUE, btree (text)
> "y_item_text_key" UNIQUE, btree (text)
now, if you check the indexes, ithe "text" column is indexed twice...
the reason is that because it is UNIQUE, postgres automatically creates
an index for it.
and then, because it has db_index = True, it gets a second index from
django.
i'm no postgresql expert, but it seems to me that having 2 indexes on
the same column is a bad thing (because when writing into this table,
the index will have to be calculated twice).
(or are they "different" indexes?)
so, should i open a bugreport (ticket) about this?
or is this intentional?
also, in this case, the "workaround" is simple. simply remove the
db_index=True.
but it's not that simple always.
for example imagine an unique SlugField. in that case the only possible
fix is to manually delete the redundant index from the db.
gabor
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