Unindexed foreign keys

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== Unindexed Foreign Keys ==
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{{SnippetInfo|Unindexed foreign keys|lang=SQL|version=... – 9.2|category=Administrative}}
 
{{SnippetInfo|Unindexed foreign keys|lang=SQL|version=... – 9.2|category=Administrative}}
 
 
== Unindexed Foreign Keys ==
 
  
 
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.
 
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.

Revision as of 14:43, 8 July 2013

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 unindexed_foreign_keys as
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    (
        select  (case when n1.nspname is not null then n1.nspname
                    else 'public' end) || '.' || c1.relname  as referencing_tbl,
                a1.attname as referencing_column,
                t.conname as existing_fk_on_referencing_tbl,
                (case when n2.nspname is not null then n2.nspname
                    else 'public' end) || '.' || c2.relname as referenced_tbl,
                a2.attname as referenced_column,
                pg_relation_size( ((case when n1.nspname is not null then n1.nspname
                                        else 'public' end) || '.' || c1.relname) ) as referencing_tbl_bytes,
                pg_relation_size( ((case when n2.nspname is not null then n2.nspname
                                        else 'public' end) || '.' || c2.relname) ) as referenced_tbl_bytes,
                'Create an index on column "' || quote_ident(a1.attname) || '" in table "' ||
                    (case when n1.nspname is not null then n1.nspname
                        else 'public' end) || '.' || c1.relname || '"' as suggestion
        from pg_constraint t
        join pg_attribute  a1 on a1.attrelid = t.conrelid and a1.attnum = t.conkey[1]
        join pg_class      c1 on c1.oid = t.conrelid
        join pg_namespace  n1 on n1.oid = c1.relnamespace
        join pg_class      c2 on c2.oid = t.confrelid
        join pg_namespace  n2 on n2.oid = c2.relnamespace
        join 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_index i
            where i.indrelid = t.conrelid
            and i.indkey[0] = t.conkey[1])
        ) as y
order by    referencing_tbl_bytes desc, referenced_tbl_bytes desc,
            referencing_tbl, referenced_tbl, referencing_column, referenced_column;
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