#31208: Index introspection fails on Postgresql in presence of schema copy
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Reporter: Shai | Owner: Shai Berger
Berger |
Type: Bug | Status: assigned
Component: Database | Version: master
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Take a normal database schema created by Django.
Duplicate it under a different schema name (e.g. `pg_dump` it into a file,
`ALTER SCHEMA public RENAME TO other`, and then `psql` the dump file).
Following this operation, index introspection fails -- if you look for an
index for a column, it will not be found, because the introspection
queries now return the columns lists doubled.
In details: For a Postgresql connection `conn`, the function
`conn.introspection.get_constraints()` returns a dictionary whose keys
are the constraint and index names and whose values are themselves
dictionaries of information for constraints and indexes. In the situation
described above, the `'columns'` entry in these dictionaries has the
contents `['column_name', 'column_name']` where it should have just
`['column_name']`. When Django code later looks for indexes for the
specified columns, it compares this entry to `['column_name']`, and since
they are not equal, the index will not be found.
Context:
We sometimes like to take database contents from one machine and recreate
the database on another.
In cases where the target database cluster already had some contents, we
like to preserve it first by renaming the schema. We usually delete the
renamed schema once the new schema creation completes successfully, but
someone forgot it and our code which relied on the introspection erred
(the schemas in our case were not exact duplicates, but similar enough).
Found this on 1.11, but the relevant code is the same on master:
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Ticket URL: <https://code.djangoproject.com/ticket/31208>
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