Improve plan when self-join table using rdb$db_key
--------------------------------------------------
Key: CORE-4528
URL: http://tracker.firebirdsql.org/browse/CORE-4528
Project: Firebird Core
Issue Type: Improvement
Affects Versions: 3.0 Alpha 2
Reporter: Pavel Zotov
Priority: Minor
Test #1
======
recreate table tn(x int);
commit;
set planonly;
var #1
--------
SQL> select * from (select x a from tn) r join (select x b from tn) s on r.a =
s.b;
PLAN HASH (S TN NATURAL, R TN NATURAL) -- OK
var #2
--------
SQL> select * from (select rdb$db_key||'' a from tn) r join (select
rdb$db_key||'' b from tn) s on r.a = s.b;
PLAN JOIN (R TN NATURAL, S TN NATURAL) -- hash join could be here
Test #2
======
create sequence g; commit;
recreate table t( id int primary key, s varchar(36) ); commit;
insert into t
select i,s from
(
select gen_id(g,1) i, uuid_to_char(gen_uuid()) s
from rdb$types a,rdb$types b,(select 1 i from rdb$types rows 20) rows 10000
)
order by rand();
commit;
var #1 (emulating left join with select only one field from driven table)
--------
select count(*) from (
select x.id, (select z.s from t z where z.rdb$db_key = x.k) s
from (select id, rdb$db_key k from t a order by id) x
)
-- works very fast:
Select Expression
-> Singularity Check
-> Filter
-> Table "T" as "Z" Access By ID
-> DBKEY
Select Expression
-> Aggregate
-> Materialize
-> Table "T" as "X A" Access By ID
-> Index "RDB$PRIMARY2" Full Scan
1 records fetched
31 ms, 50015 fetch(es)
Table Natural Index
****************************************************
T 20000
var #2 (common left join using rdb$db_key):
--------
select count(*) from (
select x.id,z.s
from (select id, rdb$db_key k from t a order by id) x
left join t z on x.k = z.rdb$db_key
);
-- works very slow:
# LI-T3.0.0.31288:
Select Expression
-> Aggregate
-> Nested Loop Join (outer)
-> Table "T" as "X A" Access By ID
-> Index "RDB$PRIMARY2" Full Scan
-> Filter
-> Table "T" as "Z" Full Scan
1 records fetched
67248 ms, 227 read(s), 204300015 fetch(es)
Table Natural Index
****************************************************
T 100000000 10000
== vs 2.5: ==
# LI-V2.5.3.26790:
49146 ms, 204300015 fetch(es)
Table Natural Index Update
***************************************************************
T 100000000 10000
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