add unused indexes script

Author: Shane Borden

postgres/postgres_find_unused_indexes.sql

@@ -0,0 +1,96 @@
+-- Copyright 2025 shaneborden
+-- 
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+-- 
+--     https://www.apache.org/licenses/LICENSE-2.0
+-- 
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+
+WITH table_scans as (
+    SELECT relid,
+        tables.idx_scan + tables.seq_scan as all_scans,
+        ( tables.n_tup_ins + tables.n_tup_upd + tables.n_tup_del ) as writes,
+                pg_relation_size(relid) as table_size
+        FROM pg_stat_all_tables as tables
+        WHERE schemaname not in ('pg_toast','pg_catalog','partman')
+),
+all_writes as (
+    SELECT sum(writes) as total_writes
+    FROM table_scans
+),
+indexes as (
+    SELECT idx_stat.relid, idx_stat.indexrelid,
+        idx_stat.schemaname, idx_stat.relname as tablename,
+        idx_stat.indexrelname as indexname,
+        idx_stat.idx_scan,
+        pg_relation_size(idx_stat.indexrelid) as index_bytes,
+        indexdef ~* 'USING btree' AS idx_is_btree
+    FROM pg_stat_user_indexes as idx_stat
+        JOIN pg_index
+            USING (indexrelid)
+        JOIN pg_indexes as indexes
+            ON idx_stat.schemaname = indexes.schemaname
+                AND idx_stat.relname = indexes.tablename
+                AND idx_stat.indexrelname = indexes.indexname
+    WHERE pg_index.indisunique = FALSE
+),
+index_ratios AS (
+SELECT schemaname, tablename, indexname,
+    idx_scan, all_scans,
+    round(( CASE WHEN all_scans = 0 THEN 0.0::NUMERIC
+        ELSE idx_scan::NUMERIC/all_scans * 100 END),2) as index_scan_pct,
+    writes,
+    round((CASE WHEN writes = 0 THEN idx_scan::NUMERIC ELSE idx_scan::NUMERIC/writes END),2)
+        as scans_per_write,
+    pg_size_pretty(index_bytes) as index_size_pretty,
+    pg_size_pretty(table_size) as table_size,
+    idx_is_btree, 
+    index_bytes as index_size_bytes
+    FROM indexes
+    JOIN table_scans
+    USING (relid)
+),
+index_groups AS (
+SELECT 'Never Used Indexes' as reason, *, 1 as grp
+FROM index_ratios
+WHERE
+    idx_scan = 0
+    and idx_is_btree
+UNION ALL
+SELECT 'Low Scans, High Writes' as reason, *, 2 as grp
+FROM index_ratios
+WHERE
+    scans_per_write <= 1
+    and index_scan_pct < 10
+    and idx_scan > 0
+    and writes > 100
+    and idx_is_btree
+UNION ALL
+SELECT 'Seldom Used Large Indexes' as reason, *, 3 as grp
+FROM index_ratios
+WHERE
+    index_scan_pct < 5
+    and scans_per_write > 1
+    and idx_scan > 0
+    and idx_is_btree
+    and index_size_bytes > 100000000
+UNION ALL
+SELECT 'High-Write Large Non-Btree' as reason, index_ratios.*, 4 as grp 
+FROM index_ratios, all_writes
+WHERE
+    ( writes::NUMERIC / ( total_writes + 1 ) ) > 0.02
+    AND NOT idx_is_btree
+    AND index_size_bytes > 100000000
+ORDER BY grp, index_size_bytes DESC )
+SELECT reason, schemaname, tablename, indexname,
+    index_scan_pct, scans_per_write, index_size_pretty,index_size_bytes, table_size
+FROM index_groups
+WHERE tablename like '%'
+ORDER BY reason, index_size_bytes,table_size;