weird hash plan cost, starting with pg10 - Mailing list pgsql-hackers

Hello

While messing with EXPLAIN on a query emitted by pg_dump, I noticed that
current Postgres 10 emits weird bucket/batch/memory values for certain
hash nodes:

                         ->  Hash  (cost=0.11..0.11 rows=10 width=12) (actual time=0.002..0.002 rows=1 loops=8)
                               Buckets: 2139062143  Batches: 2139062143  Memory Usage: 8971876904722400kB
                               ->  Function Scan on unnest init_1  (cost=0.01..0.11 rows=10 width=12) (actual
time=0.001..0.001rows=1 loops=8) 

It shows normal values in 9.6.

The complete query is:

SELECT c.tableoid, c.oid, c.relname, (SELECT pg_catalog.array_agg(acl ORDER BY row_n) FROM (SELECT acl, row_n FROM
pg_catalog.unnest(coalesce(c.relacl,pg_catalog.acldefault(CASEWHEN c.relkind = 'S' THEN 's' ELSE 'r'
END::"char",c.relowner)))WITH ORDINALITY AS perm(acl,row_n) WHERE NOT EXISTS ( SELECT 1 FROM
pg_catalog.unnest(coalesce(pip.initprivs,pg_catalog.acldefault(CASEWHEN c.relkind = 'S' THEN 's' ELSE 'r'
END::"char",c.relowner)))AS init(init_acl) WHERE acl = init_acl)) as foo) AS relacl, (SELECT pg_catalog.array_agg(acl
ORDERBY row_n) FROM (SELECT acl, row_n FROM pg_catalog.unnest(coalesce(pip.initprivs,pg_catalog.acldefault(CASE WHEN
c.relkind= 'S' THEN 's' ELSE 'r' END::"char",c.relowner))) WITH ORDINALITY AS initp(acl,row_n) WHERE NOT EXISTS (
SELECT1 FROM pg_catalog.unnest(coalesce(c.relacl,pg_catalog.acldefault(CASE WHEN c.relkind = 'S' THEN 's' ELSE 'r'
END::"char",c.relowner)))AS permp(orig_acl) WHERE acl = orig_acl)) as foo) as rrelacl, NULL AS initrelacl, NULL as
initrrelacl,c.relkind, c.relnamespace, (SELECT rolname FROM pg_catalog.pg_roles WHERE oid = c.relowner) AS rolname,
c.relchecks,c.relhastriggers, c.relhasindex, c.relhasrules, 'f'::bool AS relhasoids, c.relrowsecurity,
c.relforcerowsecurity,c.relfrozenxid, c.relminmxid, tc.oid AS toid, tc.relfrozenxid AS tfrozenxid, tc.relminmxid AS
tminmxid,c.relpersistence, c.relispopulated, c.relreplident, c.relpages, am.amname, CASE WHEN c.reloftype <> 0 THEN
c.reloftype::pg_catalog.regtypeELSE NULL END AS reloftype, d.refobjid AS owning_tab, d.refobjsubid AS owning_col,
(SELECTspcname FROM pg_tablespace t WHERE t.oid = c.reltablespace) AS reltablespace,
array_remove(array_remove(c.reloptions,'check_option=local'),'check_option=cascaded')AS reloptions, CASE WHEN
'check_option=local'= ANY (c.reloptions) THEN 'LOCAL'::text WHEN 'check_option=cascaded' = ANY (c.reloptions) THEN
'CASCADED'::textELSE NULL END AS checkoption, tc.reloptions AS toast_reloptions, c.relkind = 'S' AND EXISTS (SELECT 1
FROMpg_depend WHERE classid = 'pg_class'::regclass AND objid = c.oid AND objsubid = 0 AND refclassid =
'pg_class'::regclassAND deptype = 'i') AS is_identity_sequence, EXISTS (SELECT 1 FROM pg_attribute at LEFT JOIN
pg_init_privspip ON (c.oid = pip.objoid AND pip.classoid = 'pg_class'::regclass AND pip.objsubid = at.attnum)WHERE
at.attrelid= c.oid AND ((SELECT pg_catalog.array_agg(acl ORDER BY row_n) FROM (SELECT acl, row_n FROM
pg_catalog.unnest(coalesce(at.attacl,pg_catalog.acldefault('c',c.relowner)))WITH ORDINALITY AS perm(acl,row_n) WHERE
NOTEXISTS ( SELECT 1 FROM pg_catalog.unnest(coalesce(pip.initprivs,pg_catalog.acldefault('c',c.relowner))) AS
init(init_acl)WHERE acl = init_acl)) as foo) IS NOT NULL OR (SELECT pg_catalog.array_agg(acl ORDER BY row_n) FROM
(SELECTacl, row_n FROM pg_catalog.unnest(coalesce(pip.initprivs,pg_catalog.acldefault('c',c.relowner))) WITH ORDINALITY
ASinitp(acl,row_n) WHERE NOT EXISTS ( SELECT 1 FROM
pg_catalog.unnest(coalesce(at.attacl,pg_catalog.acldefault('c',c.relowner)))AS permp(orig_acl) WHERE acl = orig_acl))
asfoo) IS NOT NULL OR NULL IS NOT NULL OR NULL IS NOT NULL))AS changed_acl, pg_get_partkeydef(c.oid) AS partkeydef,
c.relispartitionAS ispartition, pg_get_expr(c.relpartbound, c.oid) AS partbound FROM pg_class c LEFT JOIN pg_depend d
ON(c.relkind = 'S' AND d.classid = c.tableoid AND d.objid = c.oid AND d.objsubid = 0 AND d.refclassid = c.tableoid AND
d.deptypeIN ('a', 'i')) LEFT JOIN pg_class tc ON (c.reltoastrelid = tc.oid AND c.relkind <> 'p') LEFT JOIN pg_am am ON
(c.relam= am.oid) LEFT JOIN pg_init_privs pip ON (c.oid = pip.objoid AND pip.classoid = 'pg_class'::regclass AND
pip.objsubid= 0) WHERE c.relkind in ('r', 'S', 'v', 'c', 'm', 'f', 'p') ORDER BY c.oid 

I'm not looking into this right now.  If somebody is bored in
quarantine, they might have a good time bisecting this.

--
Álvaro Herrera