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Add btree_bloat metric
Based on the bloat estimation queries from https://github.com/ioguix/pgsql-bloat-estimation
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‎internal/metrics/metrics.yaml‎

Lines changed: 117 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -4187,9 +4187,123 @@ metrics:
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pg_ls_archive_statusdir() a
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where
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name ~ '[0-9A-F]{24}.ready';
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btree_bloat:
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description:
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Estimates B-tree indexes bloat by comparing actual index size against expected size derived from pg_stats and pg_class catalog metadata.
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It reports bloat percentage, real size, extra bloat bytes, and fillfactor for each index, helping identify candidates for REINDEX or maintenance.
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Based on the bloat estimation queries from https://github.com/ioguix/pgsql-bloat-estimation.
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sqls:
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14: |-
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SELECT /* pgwatch_generated */
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(extract(epoch from now()) * 1e9)::bigint as epoch_ns,
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current_database() AS tag_dbname, nspname AS tag_schemaname, tblname AS tag_tblname, idxname as tag_idxname,
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bs*(relpages)::bigint AS real_size,
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bs*(relpages-est_pages)::bigint AS extra_size,
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100 * (relpages-est_pages)::float / relpages AS extra_pct,
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fillfactor,
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CASE WHEN relpages > est_pages_ff
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THEN bs*(relpages-est_pages_ff)
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ELSE 0
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END AS bloat_size,
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100 * (relpages-est_pages_ff)::float / relpages AS bloat_pct,
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is_na
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-- , 100-(pst).avg_leaf_density AS pst_avg_bloat, est_pages, index_tuple_hdr_bm, maxalign, pagehdr, nulldatawidth, nulldatahdrwidth, reltuples, relpages -- (DEBUG INFO)
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FROM (
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SELECT coalesce(1 +
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ceil(reltuples/floor((bs-pageopqdata-pagehdr)/(4+nulldatahdrwidth)::float)), 0 -- ItemIdData size + computed avg size of a tuple (nulldatahdrwidth)
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) AS est_pages,
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coalesce(1 +
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ceil(reltuples/floor((bs-pageopqdata-pagehdr)*fillfactor/(100*(4+nulldatahdrwidth)::float))), 0
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) AS est_pages_ff,
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bs, nspname, tblname, idxname, relpages, fillfactor, is_na
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-- , pgstatindex(idxoid) AS pst, index_tuple_hdr_bm, maxalign, pagehdr, nulldatawidth, nulldatahdrwidth, reltuples -- (DEBUG INFO)
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FROM (
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SELECT maxalign, bs, nspname, tblname, idxname, reltuples, relpages, idxoid, fillfactor,
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( index_tuple_hdr_bm +
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maxalign - CASE -- Add padding to the index tuple header to align on MAXALIGN
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WHEN index_tuple_hdr_bm%maxalign = 0 THEN maxalign
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ELSE index_tuple_hdr_bm%maxalign
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END
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+ nulldatawidth + maxalign - CASE -- Add padding to the data to align on MAXALIGN
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WHEN nulldatawidth = 0 THEN 0
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WHEN nulldatawidth::integer%maxalign = 0 THEN maxalign
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ELSE nulldatawidth::integer%maxalign
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END
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)::numeric AS nulldatahdrwidth, pagehdr, pageopqdata, is_na
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-- , index_tuple_hdr_bm, nulldatawidth -- (DEBUG INFO)
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FROM (
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SELECT n.nspname, i.tblname, i.idxname, i.reltuples, i.relpages,
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i.idxoid, i.fillfactor, current_setting('block_size')::numeric AS bs,
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CASE -- MAXALIGN: 4 on 32bits, 8 on 64bits (and mingw32 ?)
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WHEN version() ~ 'mingw32' OR version() ~ '64-bit|x86_64|ppc64|ia64|amd64' THEN 8
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ELSE 4
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END AS maxalign,
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/* per page header, fixed size: 20 for 7.X, 24 for others */
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24 AS pagehdr,
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/* per page btree opaque data */
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16 AS pageopqdata,
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/* per tuple header: add IndexAttributeBitMapData if some cols are null-able */
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CASE WHEN max(coalesce(s.null_frac,0)) = 0
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THEN 8 -- IndexTupleData size
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ELSE 8 + (( 32 + 8 - 1 ) / 8) -- IndexTupleData size + IndexAttributeBitMapData size ( max num filed per index + 8 - 1 /8)
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END AS index_tuple_hdr_bm,
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/* data len: we remove null values save space using it fractionnal part from stats */
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sum( (1-coalesce(s.null_frac, 0)) * coalesce(s.avg_width, 1024)) AS nulldatawidth,
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max( CASE WHEN i.atttypid = 'pg_catalog.name'::regtype THEN 1 ELSE 0 END ) > 0 AS is_na
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FROM (
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SELECT ct.relname AS tblname, ct.relnamespace, ic.idxname, ic.attpos, ic.indkey, ic.indkey[ic.attpos], ic.reltuples, ic.relpages, ic.tbloid, ic.idxoid, ic.fillfactor,
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coalesce(a1.attnum, a2.attnum) AS attnum, coalesce(a1.attname, a2.attname) AS attname, coalesce(a1.atttypid, a2.atttypid) AS atttypid,
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CASE WHEN a1.attnum IS NULL
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THEN ic.idxname
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ELSE ct.relname
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END AS attrelname
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FROM (
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SELECT idxname, reltuples, relpages, tbloid, idxoid, fillfactor, indkey,
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pg_catalog.generate_series(1,indnatts) AS attpos
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FROM (
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SELECT ci.relname AS idxname, ci.reltuples, ci.relpages, i.indrelid AS tbloid,
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i.indexrelid AS idxoid,
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coalesce(substring(
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array_to_string(ci.reloptions, ' ')
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from 'fillfactor=([0-9]+)')::smallint, 90) AS fillfactor,
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i.indnatts,
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pg_catalog.string_to_array(pg_catalog.textin(
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pg_catalog.int2vectorout(i.indkey)),' ')::int[] AS indkey
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FROM pg_catalog.pg_index i
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JOIN pg_catalog.pg_class ci ON ci.oid = i.indexrelid
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WHERE ci.relam=(SELECT oid FROM pg_am WHERE amname = 'btree')
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AND ci.relpages > 0
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) AS idx_data
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) AS ic
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JOIN pg_catalog.pg_class ct ON ct.oid = ic.tbloid
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LEFT JOIN pg_catalog.pg_attribute a1 ON
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ic.indkey[ic.attpos] <> 0
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AND a1.attrelid = ic.tbloid
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AND a1.attnum = ic.indkey[ic.attpos]
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LEFT JOIN pg_catalog.pg_attribute a2 ON
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ic.indkey[ic.attpos] = 0
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AND a2.attrelid = ic.idxoid
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AND a2.attnum = ic.attpos
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) i
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JOIN pg_catalog.pg_namespace n ON n.oid = i.relnamespace
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JOIN pg_catalog.pg_stats s ON s.schemaname = n.nspname
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AND s.tablename = i.attrelname
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AND s.attname = i.attname
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GROUP BY 1,2,3,4,5,6,7,8,9,10,11
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) AS rows_data_stats
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) AS rows_hdr_pdg_stats
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) AS relation_stats
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WHERE (bs * relpages::float / (1024 * 1024)) > 1 /* exclude indexes below 1 MiB */
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ORDER BY is_na, bloat_pct desc
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LIMIT 100
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gauges:
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- real_size
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- extra_size
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- extra_pct
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- fillfactor
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- bloat_size
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- bloat_pct
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- is_na
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presets:
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aiven:
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description: aiven database metrics

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