As proposed by timgraham in https://code.djangoproject.com/ticket/24507 I
open the discussion here.
When adding db_index=True on a CharField Django automatically create 2
indexes on some backends as PostgreSQL. But in usage the second index is
not always necessary if you never use contains() or similar queries. As you
can see here I extracted indexes usages statistics from one of our
production server.
The index *foo_bar_email_from_create_like* is never use even if
*foo_bar_email_from_create* is, and if we look on our queries this is
totally logic and regular. And it's the same for *foo_bar_tech_id* and
*foo_bar_user_type*, and it's the same on the other table.
indexrelname | idx_scan | idx_tup_read |
idx_tup_fetch
--------------------------------------+------------+--------------+--------------
foo_bar_address_like | 0 | 0 |
0
foo_bar_current_profile_id | 1846 | 617 |
236
foo_bar_date_delete | 0 | 0 |
0
foo_bar_email_from_create | 31209 | 90886 |
21903
foo_bar_email_from_create_like | 0 | 0 |
0
foo_bar_entity_id | 8026 | 28957 |
14
foo_bar_pkey | 1258565593 | 1418841848 |
1194873240
foo_bar_site_id | 4495829 | 51000840065 |
3564
foo_bar_tech_id | 25045160 | 28233693 |
25087324
foo_bar_tech_id_like | 0 | 0 |
0
foo_bar_user_type | 21428 | 263769329 |
216686751
foo_bar_user_type_like | 0 | 0 |
0
foo_bar_uuid_like | 0 | 0 |
0
foo_bar_uuid_uniq | 13134415 | 13157636 |
12928178
A last point is each index on this table is consumming more the 2Gb on disk.
Even if we can suppress the indexes, and this is what we do with
(https://github.com/novafloss/django-json-dbindex) on bigger one realy
problematic, we'd prefer to not create them.
Thanks for your time and this wonderful project Django is.
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