Fix a join in the postgres_indexes view

Change the join condition in the postgres_indexes view that joins only
by index name, instead of by both index name and schema. If we have two
indexes in different schema with the same name, the previous join would
return extra rows.

Changelog: fixed

db/migrate/20211018161447_fix_double_entries_in_postgres_index_view.rb

+# frozen_string_literal: true
+
+class FixDoubleEntriesInPostgresIndexView < Gitlab::Database::Migration[1.0]
+  def up
+    execute(<<~SQL)
+      DROP VIEW IF EXISTS postgres_indexes;
+
+      CREATE VIEW postgres_indexes AS
+      SELECT (pg_namespace.nspname::text || '.'::text) || i.relname::text AS identifier,
+        pg_index.indexrelid,
+        pg_namespace.nspname AS schema,
+        i.relname AS name,
+        pg_indexes.tablename,
+        a.amname AS type,
+        pg_index.indisunique AS "unique",
+        pg_index.indisvalid AS valid_index,
+        i.relispartition AS partitioned,
+        pg_index.indisexclusion AS exclusion,
+        pg_index.indexprs IS NOT NULL AS expression,
+        pg_index.indpred IS NOT NULL AS partial,
+        pg_indexes.indexdef AS definition,
+        pg_relation_size(i.oid::regclass) AS ondisk_size_bytes
+      FROM pg_index
+        JOIN pg_class i ON i.oid = pg_index.indexrelid
+        JOIN pg_namespace ON i.relnamespace = pg_namespace.oid
+        JOIN pg_indexes ON i.relname = pg_indexes.indexname AND pg_namespace.nspname = pg_indexes.schemaname
+        JOIN pg_am a ON i.relam = a.oid
+      WHERE pg_namespace.nspname <> 'pg_catalog'::name AND (pg_namespace.nspname = ANY (ARRAY["current_schema"(), 'gitlab_partitions_dynamic'::name, 'gitlab_partitions_static'::name]));
+    SQL
+  end
+
+  def down
+    execute(<<~SQL)
+      DROP VIEW IF EXISTS postgres_indexes;
+
+      CREATE VIEW postgres_indexes AS
+      SELECT (pg_namespace.nspname::text || '.'::text) || i.relname::text AS identifier,
+        pg_index.indexrelid,
+        pg_namespace.nspname AS schema,
+        i.relname AS name,
+        pg_indexes.tablename,
+        a.amname AS type,
+        pg_index.indisunique AS "unique",
+        pg_index.indisvalid AS valid_index,
+        i.relispartition AS partitioned,
+        pg_index.indisexclusion AS exclusion,
+        pg_index.indexprs IS NOT NULL AS expression,
+        pg_index.indpred IS NOT NULL AS partial,
+        pg_indexes.indexdef AS definition,
+        pg_relation_size(i.oid::regclass) AS ondisk_size_bytes
+      FROM pg_index
+        JOIN pg_class i ON i.oid = pg_index.indexrelid
+        JOIN pg_namespace ON i.relnamespace = pg_namespace.oid
+        JOIN pg_indexes ON i.relname = pg_indexes.indexname
+        JOIN pg_am a ON i.relam = a.oid
+      WHERE pg_namespace.nspname <> 'pg_catalog'::name AND (pg_namespace.nspname = ANY (ARRAY["current_schema"(), 'gitlab_partitions_dynamic'::name, 'gitlab_partitions_static'::name]));
+    SQL
+  end
+end

db/schema_migrations/20211018161447

+168b383c4a85de35ade8a26e442ca49a40342ba05fb23fab4f0444814d976f65
\ No newline at end of file

db/structure.sql

@@ -17661,7 +17661,7 @@ CREATE VIEW postgres_indexes AS
    FROM ((((pg_index
      JOIN pg_class i ON ((i.oid = pg_index.indexrelid)))
      JOIN pg_namespace ON ((i.relnamespace = pg_namespace.oid)))
-     JOIN pg_indexes ON ((i.relname = pg_indexes.indexname)))
+     JOIN pg_indexes ON (((i.relname = pg_indexes.indexname) AND (pg_namespace.nspname = pg_indexes.schemaname))))
      JOIN pg_am a ON ((i.relam = a.oid)))
   WHERE ((pg_namespace.nspname <> 'pg_catalog'::name) AND (pg_namespace.nspname = ANY (ARRAY["current_schema"(), 'gitlab_partitions_dynamic'::name, 'gitlab_partitions_static'::name])));