#27323: Using USER_SEQUENCES instead of USER_CATALOG
-------------------------------------+-------------------------------------
Reporter: felixxm | Owner: felixxm
Type: | Status: assigned
Cleanup/optimization |
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: Oracle sequences | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by felixxm):
Replying to [comment:5 Tim Graham]:
> Could you explain why it's more optimal so we have that rationale
recorded?
Query with `USER_CATALOG` has a cost equal **3** and it has **2**
conditions in WHERE clause.
Query with `USER_SEQUENCES` has a cost equal **2** and it has **1**
condition in WHERE clause.
`USER_CATALOG` is quite complicate, it depends on the
`_CURRENT_EDITION_OBJ` and it contains all of the user objects from which
we are choosing sequences:
{{{#!sql
CREATE OR REPLACE FORCE VIEW "SYS"."_CURRENT_EDITION_OBJ" ("OBJ#",
"DATAOBJ#", "DEFINING_OWNER#", "NAME", "NAMESPACE", "SUBNAME", "TYPE#",
"CTIME", "MTIME", "STIME", "STATUS", "REMOTEOWNER", "LINKNAME", "FLAGS",
"OID$", "SPARE1", "SPARE2", "SPARE3", "SPARE4", "SPARE5", "SPARE6",
"OWNER#", "DEFINING_EDITION") AS
select
o."OBJ#",o."DATAOBJ#",o."OWNER#",o."NAME",o."NAMESPACE",o."SUBNAME",o."TYPE#",o."CTIME",o."MTIME",o."STIME",o."STATUS",o."REMOTEOWNER",o."LINKNAME",o."FLAGS",o."OID$",o."SPARE1",o."SPARE2",o."SPARE3",o."SPARE4",o."SPARE5",o."SPARE6",
o.spare3,
case when (o.type# not in (4,5,7,8,9,10,11,12,13,14,22,87) or
bitand(u.spare1, 16) = 0) then
null
when (u.type# = 2) then
(select eo.name from obj$ eo where eo.obj# = u.spare2)
else
'ORA$BASE'
end
from obj$ o, user$ u
where o.owner# = u.user#
and ( /* non-versionable object */
( o.type# not in (4,5,7,8,9,10,11,12,13,14,22,87,88)
or bitand(u.spare1, 16) = 0)
/* versionable object visible in current edition */
or ( o.type# in (4,5,7,8,9,10,11,12,13,14,22,87)
and ( (u.type# <> 2 and
sys_context('userenv', 'current_edition_name') =
'ORA$BASE')
or (u.type# = 2 and
u.spare2 = sys_context('userenv',
'current_edition_id'))
or exists (select 1 from obj$ o2, user$ u2
where o2.type# = 88
and o2.dataobj# = o.obj#
and o2.owner# = u2.user#
and u2.type# = 2
and u2.spare2 =
sys_context('userenv',
'current_edition_id'))
)
)
);
}}}
`USER_SEQUENCES` is much more readable and it contains only sequences:
{{{#!sql
CREATE OR REPLACE FORCE VIEW "SYS"."USER_SEQUENCES" ("SEQUENCE_NAME",
"MIN_VALUE", "MAX_VALUE", "INCREMENT_BY", "CYCLE_FLAG", "ORDER_FLAG",
"CACHE_SIZE", "LAST_NUMBER") AS
select o.name,
s.minvalue, s.maxvalue, s.increment$,
decode (s.cycle#, 0, 'N', 1, 'Y'),
decode (s.order$, 0, 'N', 1, 'Y'),
s.cache, s.highwater
from sys.seq$ s, sys.obj$ o
where o.owner# = userenv('SCHEMAID')
and o.obj# = s.obj#;
}}}
To sum up, in the first approach we choose all objects (including
sequences), and in the second step we limit results to sequences with the
given name. In the second approach we choose sequences and next limit
results to the given name.
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Ticket URL: <https://code.djangoproject.com/ticket/27323#comment:6>
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