Unindexed foreign keys

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Unindexed Foreign Keys

Administrative Snippets

Unindexed foreign keys

Works with PostgreSQL

... – 9.2

Written in

SQL

Depends on

Nothing


I'm not sure of the original source of this query, but it might be from Michael Fuhr in the pgsql-performance mailing lists back in 2007.

It has been modified in several ways:

  • Size of referencing and referenced tables added,
  • Suggestion on index to add,
  • Searches only for single-column or compound indexes where the leading column is the referencing key.

Tested in PostgreSQL 9.2 (might work with earlier versions).

CREATE OR REPLACE VIEW admin.unindexed_foreign_keys AS
WITH y AS (
    SELECT
        pg_catalog.format('%I.%I', n1.nspname, c1.relname)  AS referencing_tbl,
        pg_catalog.quote_ident(a1.attname) AS referencing_column,
        t.conname AS existing_fk_on_referencing_tbl,
        pg_catalog.format('%I.%I', n2.nspname, c2.relname) AS referenced_tbl,
        pg_catalog.quote_ident(a2.attname) AS referenced_column,
        pg_relation_size( pg_catalog.format('%I.%I', n1.nspname, c1.relname) ) AS referencing_tbl_bytes,
        pg_relation_size( pg_catalog.format('%I.%I', n2.nspname, c2.relname) ) AS referenced_tbl_bytes,
        pg_catalog.format($$CREATE INDEX ON %I.%I(%I);$$, n1.nspname, c1.relname, a1.attname) AS suggestion
    FROM pg_catalog.pg_constraint t
    JOIN pg_catalog.pg_attribute  a1 ON a1.attrelid = t.conrelid AND a1.attnum = t.conkey[1]
    JOIN pg_catalog.pg_class      c1 ON c1.oid = t.conrelid
    JOIN pg_catalog.pg_namespace  n1 ON n1.oid = c1.relnamespace
    JOIN pg_catalog.pg_class      c2 ON c2.oid = t.confrelid
    JOIN pg_catalog.pg_namespace  n2 ON n2.oid = c2.relnamespace
    JOIN pg_catalog.pg_attribute  a2 ON a2.attrelid = t.confrelid AND a2.attnum = t.confkey[1]
    WHERE t.contype = 'f'
    AND NOT EXISTS (
        SELECT 1
        FROM pg_catalog.pg_index i
        WHERE i.indrelid = t.conrelid
        AND i.indkey[0] = t.conkey[1]
    )
)
SELECT  referencing_tbl,
        referencing_column,
        existing_fk_on_referencing_tbl,
        referenced_tbl,
        referenced_column,
        pg_size_pretty(referencing_tbl_bytes) AS referencing_tbl_size,
        pg_size_pretty(referenced_tbl_bytes) AS referenced_tbl_size,
        suggestion
FROM y
ORDER BY
    referencing_tbl_bytes DESC,
    referenced_tbl_bytes DESC,
    referencing_tbl,
    referenced_tbl,
    referencing_column,
    referenced_column;
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