-- Originally from: https://github.com/ioguix/pgsql-bloat-estimation/blob/master/btree/btree_bloat.sql
-- WARNING: executed with a non-superuser role, the query inspect only index on tables you are granted to read.
-- WARNING: rows with is_na = 't' are known to have bad statistics ("name" type is not supported).
-- This query is compatible with PostgreSQL 8.2 and after
SELECT current_database(), nspname AS schemaname, tblname, idxname AS object_name, bs*(relpages)::bigint AS real_size,
  bs*(relpages-est_pages)::bigint AS extra_size,
  100 * (relpages-est_pages)::float / relpages AS extra_ratio,
  fillfactor,
  CASE WHEN relpages > est_pages_ff
    THEN bs*(relpages-est_pages_ff)
    ELSE 0
  END AS bloat_size,
  100 * (relpages-est_pages_ff)::float / relpages AS bloat_ratio,
  is_na
  -- , 100-(sub.pst).avg_leaf_density, est_pages, index_tuple_hdr_bm, maxalign, pagehdr, nulldatawidth, nulldatahdrwidth, sub.reltuples, sub.relpages -- (DEBUG INFO)
FROM (
  SELECT coalesce(1 +
       ceil(reltuples/floor((bs-pageopqdata-pagehdr)/(4+nulldatahdrwidth)::float)), 0 -- ItemIdData size + computed avg size of a tuple (nulldatahdrwidth)
    ) AS est_pages,
    coalesce(1 +
       ceil(reltuples/floor((bs-pageopqdata-pagehdr)*fillfactor/(100*(4+nulldatahdrwidth)::float))), 0
    ) AS est_pages_ff,
    bs, nspname, table_oid, tblname, idxname, relpages, fillfactor, is_na
    -- , stattuple.pgstatindex(quote_ident(nspname)||'.'||quote_ident(idxname)) AS pst, index_tuple_hdr_bm, maxalign, pagehdr, nulldatawidth, nulldatahdrwidth, reltuples -- (DEBUG INFO)
  FROM (
    SELECT maxalign, bs, nspname, tblname, idxname, reltuples, relpages, relam, table_oid, fillfactor,
      ( index_tuple_hdr_bm +
          maxalign - CASE -- Add padding to the index tuple header to align on MAXALIGN
            WHEN index_tuple_hdr_bm%maxalign = 0 THEN maxalign
            ELSE index_tuple_hdr_bm%maxalign
          END
        + nulldatawidth + maxalign - CASE -- Add padding to the data to align on MAXALIGN
            WHEN nulldatawidth = 0 THEN 0
            WHEN nulldatawidth::integer%maxalign = 0 THEN maxalign
            ELSE nulldatawidth::integer%maxalign
          END
      )::numeric AS nulldatahdrwidth, pagehdr, pageopqdata, is_na
      -- , index_tuple_hdr_bm, nulldatawidth -- (DEBUG INFO)
    FROM (
      SELECT
        i.nspname, i.tblname, i.idxname, i.reltuples, i.relpages, i.relam, a.attrelid AS table_oid,
        current_setting('block_size')::numeric AS bs, fillfactor,
        CASE -- MAXALIGN: 4 on 32bits, 8 on 64bits (and mingw32 ?)
          WHEN version() ~ 'mingw32' OR version() ~ '64-bit|x86_64|ppc64|ia64|amd64' THEN 8
          ELSE 4
        END AS maxalign,
        /* per page header, fixed size: 20 for 7.X, 24 for others */
        24 AS pagehdr,
        /* per page btree opaque data */
        16 AS pageopqdata,
        /* per tuple header: add IndexAttributeBitMapData if some cols are null-able */
        CASE WHEN max(coalesce(s.null_frac,0)) = 0
          THEN 2 -- IndexTupleData size
          ELSE 2 + (( 32 + 8 - 1 ) / 8) -- IndexTupleData size + IndexAttributeBitMapData size ( max num filed per index + 8 - 1 /8)
        END AS index_tuple_hdr_bm,
        /* data len: we remove null values save space using it fractionnal part from stats */
        sum( (1-coalesce(s.null_frac, 0)) * coalesce(s.avg_width, 1024)) AS nulldatawidth,
        max( CASE WHEN a.atttypid = 'pg_catalog.name'::regtype THEN 1 ELSE 0 END ) > 0 AS is_na
      FROM pg_attribute AS a
        JOIN (
          SELECT nspname, tbl.relname AS tblname, idx.relname AS idxname, idx.reltuples, idx.relpages, idx.relam,
            indrelid, indexrelid, indkey::smallint[] AS attnum,
            coalesce(substring(
              array_to_string(idx.reloptions, ' ')
               from 'fillfactor=([0-9]+)')::smallint, 90) AS fillfactor
          FROM pg_index
            JOIN pg_class idx ON idx.oid=pg_index.indexrelid
            JOIN pg_class tbl ON tbl.oid=pg_index.indrelid
            JOIN pg_namespace ON pg_namespace.oid = idx.relnamespace
          WHERE pg_index.indisvalid AND tbl.relkind = 'r' AND idx.relpages > 0
        ) AS i ON a.attrelid = i.indexrelid
        JOIN pg_stats AS s ON s.schemaname = i.nspname
          AND ((s.tablename = i.tblname AND s.attname = pg_catalog.pg_get_indexdef(a.attrelid, a.attnum, TRUE)) -- stats from tbl
          OR   (s.tablename = i.idxname AND s.attname = a.attname))-- stats from functionnal cols
        JOIN pg_type AS t ON a.atttypid = t.oid
      WHERE a.attnum > 0
      GROUP BY 1, 2, 3, 4, 5, 6, 7, 8, 9
    ) AS s1
  ) AS s2
    JOIN pg_am am ON s2.relam = am.oid WHERE am.amname = 'btree'
) AS sub
WHERE NOT is_na
AND   nspname = 'public'
ORDER BY 2,3,4;