RE: DB grow overtime with autovacuum (postgres 9.6.9)

You need to find why the autovacuum is not completing. Use the following
to find the tables that have not been updated - its more than likely to be
the xmin horizon issue due to long running uncommitted transactions.

WITH constants

AS (SELECT

current_setting('autovacuum_vacuum_scale_factor')::float8 AS
autovacuum_vacuum_scale_factor,

current_setting('autovacuum_vacuum_threshold')::float8 AS
autovacuum_vacuum_threshold,

1000000 AS
autovacuum_vacuum_threshold_trigger

)

SELECT

t.schemaname AS
"SchemaName",

t.relname AS
"TableName",

TO_CHAR(t.n_tup_ins, 'fm999G999G999G990') AS
"Inserts",

TO_CHAR(t.n_tup_upd, 'fm999G999G999G990') AS
"Updates",

TO_CHAR(t.n_tup_del, 'fm999G999G999G990') AS
"Deletes",

TO_CHAR(c.reltuples, 'fm999G999G999G990') AS
"AnalyzedTuples",

CASE WHEN c.reltuples < t.n_live_tup THEN '<' WHEN c.reltuples >
t.n_live_tup THEN '>' ELSE '' END

AS "Stale",

TO_CHAR(t.n_live_tup,'fm999G999G999G990') AS
"LiveTuples",

TO_CHAR(t.n_dead_tup,'fm999G999G999G990') AS
"DeadTuples",

TO_CHAR(LEAST(99.999,n_dead_tup::float4/GREATEST(1,n_live_tup)::float4*100),'fm990D00%')

AS
"DeadRatio", --Limit to 1000%

TO_CHAR(c.reltuples *
COALESCE(SPLIT_PART(c.reloptions[1],'=',2)::float8,autovacuum_vacuum_scale_factor)
+ autovacuum_vacuum_threshold,'fm999G999G990')

AS
"AutoVacuumTrigger",

CASE WHEN t.n_dead_tup > c.reltuples *
COALESCE(SPLIT_PART(c.reloptions[1],'=',2)::float8,autovacuum_vacuum_scale_factor)
+ autovacuum_vacuum_threshold THEN '*' ELSE '' END

AS
"ShouldVacuum",

TO_CHAR(COALESCE(SPLIT_PART(c.reloptions[1],'=',2)::float8,autovacuum_vacuum_scale_factor)*100,'fm999G990D00%')

AS
"CurrentScaleFactor",

CASE WHEN c.reltuples *
COALESCE(SPLIT_PART(c.reloptions[1],'=',2)::float8,autovacuum_vacuum_scale_factor)
+ autovacuum_vacuum_threshold > autovacuum_vacuum_threshold_trigger

THEN
TO_CHAR(autovacuum_vacuum_threshold_trigger,'fm999G999G990') --threshold
instead of scale factor

ELSE
TO_CHAR(COALESCE(SPLIT_PART(c.reloptions[1],'=',2)::float8,autovacuum_vacuum_scale_factor)*100,'fm999G990D00%')

END AS
"SuggestedScaleFactor",

t.last_analyze,

t.last_autoanalyze,

t.last_vacuum,

t.last_autovacuum,

t.analyze_count AS analyzecount,

t.autoanalyze_count AS autoanalyzecount,

t.vacuum_count AS vacuumcount,

t.autovacuum_count AS autovacuumcount,

pg_size_pretty(pg_total_relation_size(c.oid)) AS
totalSize,

pg_size_pretty(pg_indexes_size(c.oid)) AS
indexSize,

pg_size_pretty(COALESCE(pg_total_relation_size(c.reltoastrelid),0))
AS ToastSize

FROM pg_stat_user_tables AS t

JOIN pg_class AS c ON c.relname=t.relname

JOIN pg_catalog.pg_namespace AS n ON n.oid = c.relnamespace AND
n.nspname=t.schemaname

CROSS JOIN constants

WHERE (t.n_live_tup > 0 AND

t.n_dead_tup > GREATEST(100000,c.reltuples *
autovacuum_vacuum_scale_factor + autovacuum_vacuum_threshold) --more than
10k dead tuples or dead tuples exceed threshold

)

-- OR c.reltuples * autovacuum_vacuum_scale_factor +
autovacuum_vacuum_threshold > autovacuum_vacuum_threshold_trigger -- the
autovacuum threshold is over threshold - might need reducing

ORDER BY 1,2;

If you manually vacuum verbose analyze for one of the tables this reports
on, it should then tell you the minimum xmin value (which is the horizon).

If you then look in pg_stat_activity it should tell you the transactions
that are preventing the horizon from moving forward

select * from pg_stat_activity where backend_xmin::text::bigint <=
<*minimum_xmin
value here*> order by xact_start

eg

select * from pg_stat_activity where backend_xmin::text::bigint <=
422050991 order by xact_start

regards

Captain.Glumbo 😊

*From:* Avihai Shoham <avihai(dot)shoham(at)gmail(dot)com>
*Sent:* 01 March 2022 12:21
*To:* pgsql-admin(at)lists(dot)postgresql(dot)org
*Subject:* DB grow overtime with autovacuum (postgres 9.6.9)

Hi All,

We use postgres 9.6.9

we set the following autovacuum setting , but still the DB grow overtime

autovacuum = on
work_mem= 50MB
wal_buffers= -1
synchronous_commit=off
log_autovacuum_min_duration = 0
autovacuum_vacuum_scale_factor = 0.1
autovacuum_analyze_scale_factor = 0.05
autovacuum_vacuum_threshold = 25
autovacuum_max_workers= 6
autovacuum_naptime = 10s
autovacuum_vacuum_cost_delay = 10ms
autovacuum_vacuum_cost_limit = -1
autovacuum_freeze_max_age = 1000000000
autovacuum_multixact_freeze_max_age = 400000000
autovacuum_work_mem = -1
autovacuum_analyze_threshold = 10

we have

any idea ?

DB size grew from 11G to 25G in 2wks.

I read that we may need to increase the max_fsm_pages setting. not sure if
it is needed if we have autovacuum or how to do it if needed?

Thank you all

Avihai

Graham Myers