PostgresDB Vacuum Issues
Autovacuum not running efficiently, leading to bloat in tables or indexes and causing performance issues.
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What is
PostgresDB Vacuum Issues
?
- Check for Long-Running Transactions:
- Query to find long-running transactions:
SELECT pid, age(clock_timestamp(), query_start), usename, query
FROM pg_stat_activity
WHERE state IN ('idle in transaction', 'active')
ORDER BY query_start;- If any transactions are running longer than expected, consider terminating them (if safe) using:
SELECT pg_terminate_backend(pid);
- Analyze Table Bloat:
- Use the following query to identify table and index bloat:
SELECT schemaname, tablename, pg_size_pretty(real_size) AS real_size,
pg_size_pretty(extra_size) AS extra_size, extra_size::float / real_size::float * 100 AS extra_pct,
fillfactor, (real_size - otta) AS wastedbytes
FROM (
SELECT schemaname, tablename, cc.reltuples, cc.relpages, bs,
CEIL((cc.reltuples*((datahdr+ma-
(CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))+nullhdr2+4))
/ (bs-20::float)) AS otta,
COALESCE(ceil(relpages/((bs-20::float)/((datahdr+ma-
(CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))+nullhdr2+4))::numeric), 0) AS expectedpages,
relpages, fillfactor, (bs*(cc.relpages-otta)) AS extra_size,
(ceil(relpages/((bs-20::float)/((datahdr+ma-
(CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))+nullhdr2+4))::numeric)-otta)::int AS unusedpages,
CASE WHEN relpages > otta THEN bs*(relpages-otta)::bigint ELSE 0 END AS real_size
FROM (
SELECT ma,bs,schemaname,tablename,
(datawidth+(hdr+ma-(CASE WHEN hdr%ma=0 THEN ma ELSE hdr%ma END))/4)*(CASE WHEN hdr%ma=0 THEN 1 ELSE 2 END) AS datahdr,
(maxfracsum*(nullhdr+ma-(CASE WHEN nullhdr%ma=0 THEN ma ELSE nullhdr%ma END))/4) AS nullhdr2,
hdr, fillfactor, reltuples, relpages, pg_class.oid
FROM (
SELECT ns.nspname AS schemaname, tbl.relname AS tablename, tbl.reltuples,
tbl.relpages, tbl.reltoastrelid, tbl.reloptions, tbl.oid,
coalesce(substring(
array_to_string(tbl.reloptions, ' ')
FROM 'fillfactor=([0-9]+)')::smallint, 100) AS fillfactor,
current_setting('block_size')::numeric AS bs,
CASE WHEN tbl.relhasoids THEN 24 ELSE 8 END AS hdr,
sum((1-coalesce(s.null_frac,0)) * coalesce(s.avg_width, 2048) + (CASE WHEN s.data_type='numeric' THEN 12 ELSE 0 END)) AS datawidth,
max(coalesce(s.null_frac,0)) AS maxfracsum,
hdr+(
CASE WHEN max(coalesce(s.null_frac,0)) > 0 THEN
coalesce(nullhdr, 23)
ELSE
23
END
) AS nullhdr,
count(s.*) AS ma
FROM pg_attribute s
JOIN pg_class tbl ON s.attrelid = tbl.oid
JOIN pg_namespace ns ON ns.oid = tbl.relnamespace
LEFT JOIN pg_stats y ON s.attrelid=y.tableoid AND s.attnum=y.attnum
LEFT JOIN (
SELECT
CASE WHEN count(*) > 1 THEN 32 ELSE 16 END AS nullhdr,
CASE WHEN count(*) = 0 THEN 0 ELSE sum((1-coalesce(s.null_frac,0))*coalesce(s.avg_width, 2048))::int END AS datahdr,
max(attrelid) AS attrelid
FROM pg_attribute s
JOIN pg_stats y ON s.attrelid=y.tableoid AND s.attnum=y.attnum
WHERE s.attnum > 0
GROUP BY s.attrelid
) AS g ON s.attrelid=g.attrelid
WHERE s.attnum > 0
GROUP BY 1,2,3,4,5,6,7,8,9,10
) AS foo
) AS rs
JOIN pg_class cc ON cc.oid=rs.oid
JOIN pg_namespace nn ON cc.relnamespace = nn.oid AND nn.nspname <> 'information_schema'
) AS sml
ORDER BY wastedbytes DESC;- This query will highlight tables that may benefit from vacuuming or reindexing due to bloat.
- Manual Vacuum and Analyze:
- If specific tables are identified as bloated, consider manually vacuuming or analyzing them:
VACUUM (VERBOSE, ANALYZE) table_name;- For critical production systems, use
VACUUMwithoutFULLto avoid exclusive locks.
- Monitor Vacuum Processes:
- To monitor ongoing vacuum processes:
SELECT pid, phase, relation::regclass, query, age(clocktimestamp(), querystart) AS runningfor
FROM pgstat_activity
WHERE query ~* '^autovacuum:' AND state = 'active';
- To monitor ongoing vacuum processes:
These actions, taken immediately upon noticing vacuum issues, can help in identifying and mitigating the root causes of the problems.
Attached error:
PostgresDB Vacuum Issues
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