Oracle SQL | Monthly Archives: June 2019

Recently I got a question: why CBO chooses “FIXED TABLE FULL TABLE” scan instead of “FIXED INDEX” in case of a join to flashback_transaction_query view with the predicate “q.xid = a.versions_xid”:

select
  versions_xid,
  versions_startscn,
  versions_starttime,
  versions_endscn,
  versions_endtime,
  --scn_to_timestamp,
  to_char(a.classification), a.* 
from vms.advisory_arch_20190624 versions between
         timestamp timestamp'2019-06-24 13:28:00' and maxvalue a
    join flashback_transaction_query q
      on q.xid = a.versions_xid
 where a.advisoryid = 100511;

As you can see flashback_transaction_query is just a wrapper view for SYS.X$KTUQQRY, ie fixed table, which obviously has good “fixed index” for that:

And simple query with the predicate xid=hextoraw(…) uses it:

In such cases we need to check another part of the equality predicate, because usually it means that we use some function instead of literal, bind variable or SQL operator. Simple example with v$session_event:

explain plan for
SELECT SUM(E.TIME_WAITED)/100 AS TIME_WAITED 
FROM V$SESSION_EVENT E 
WHERE E.SID = SYS_CONTEXT('userenv', 'sid')
AND (E.EVENT = 'TCP Socket (KGAS)' OR E.EVENT LIKE 'SQL*Net%dblink');

But it works fine with bind variables or if we use “precompute_subquery” hint to replace function call with the computed literal:

SQL> explain plan for
  2  SELECT  SUM(E.TIME_WAITED)/100 AS TIME_WAITED
  3  FROM  V$SESSION_EVENT E
  4  WHERE E.SID = :sid
  5    AND (E.EVENT = 'TCP Socket (KGAS)' OR E.EVENT LIKE 'SQL*Net%dblink');

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------------
Plan hash value: 404853953

---------------------------------------------------------------------------------------------
| Id  | Operation                 | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT          |                 |     1 |    47 |     1 (100)| 00:00:01 |
|   1 |  SORT AGGREGATE           |                 |     1 |    47 |            |          |
|   2 |   NESTED LOOPS            |                 |     3 |   141 |     1 (100)| 00:00:01 |
|*  3 |    FIXED TABLE FIXED INDEX| X$KSLES (ind:1) |   403 |  6851 |     1 (100)| 00:00:01 |
|*  4 |    FIXED TABLE FIXED INDEX| X$KSLED (ind:2) |     1 |    30 |     0   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - filter("S"."KSLESSID"=TO_NUMBER(:SID) AND "S"."KSLESWTS"<>0 AND
              "S"."INST_ID"=USERENV('INSTANCE'))
   4 - filter(("D"."KSLEDNAM"='TCP Socket (KGAS)' OR "D"."KSLEDNAM" LIKE
              'SQL*Net%dblink') AND "S"."KSLESENM"="D"."INDX")
---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
  1  explain plan for
  2  SELECT SUM(E.TIME_WAITED)/100 AS TIME_WAITED
  3  FROM
  4   V$SESSION_EVENT E
  5  WHERE E.SID in (select/*+ precompute_subquery */ SYS_CONTEXT('userenv', 'sid') from dual) AND (E.EVENT =
  6*   'TCP Socket (KGAS)' OR E.EVENT LIKE 'SQL*Net%dblink')
SQL> /

Explained.

SQL> @xplan ""



PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------------
Plan hash value: 2330447422

---------------------------------------------------------------------------------------------
| Id  | Operation                 | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT          |                 |     1 |    50 |     0   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE           |                 |     1 |    50 |            |          |
|   2 |   NESTED LOOPS            |                 |     3 |   150 |     0   (0)| 00:00:01 |
|*  3 |    FIXED TABLE FIXED INDEX| X$KSLES (ind:1) |   514 | 10280 |     0   (0)| 00:00:01 |
|*  4 |    FIXED TABLE FIXED INDEX| X$KSLED (ind:2) |     1 |    30 |     0   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - filter("S"."KSLESSID"=382 AND "S"."KSLESWTS"<>0 AND ("S"."CON_ID"=0 OR
              "S"."CON_ID"=3) AND "S"."INST_ID"=USERENV('INSTANCE'))
   4 - filter("S"."KSLESENM"="D"."INDX" AND ("D"."KSLEDNAM"='TCP Socket (KGAS)' OR
              "D"."KSLEDNAM" LIKE 'SQL*Net%dblink'))

19 rows selected.

So the same problem we got with flashback_transaction_query, because VERSIONS_XID is a pseudocolumn in fact (ie function). So we can easily hide it in inline view:

SQL> ;
  1  explain plan for
  2  with a as (
  3  select/*+ no_merge */
  4         versions_xid, versions_startscn, versions_starttime, versions_endscn, versions_endtime, --scn_to_timestamp,
  5         to_char(x.classification),
  6         x.*
  7    from advisory_arch_20190624 versions between timestamp to_timestamp('2019-06-25 22:14:00', 'YYYY-MM-DD HH24:MI:SS') and maxvalue x
  8    where x.advisoryid = 100511
  9  )
 10  select/*+ leading(a q) use_nl(q) index(q (xid)) */ *
 11  from a
 12*      join flashback_transaction_query q on q.xid = a.versions_xid
SQL> /

Explained.

SQL> @xplan +outline

P_FORMAT
------------------------
typical +outline

1 row selected.


PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------------------------
Plan hash value: 2200855354

---------------------------------------------------------------------------------------------------
| Id  | Operation                | Name                   | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT         |                        |     1 |  2596 |     6   (0)| 00:00:01 |
|   1 |  NESTED LOOPS            |                        |     1 |  2596 |     6   (0)| 00:00:01 |
|   2 |   VIEW                   |                        |     1 |    98 |     6   (0)| 00:00:01 |
|*  3 |    TABLE ACCESS FULL     | ADVISORY_ARCH_20190624 |     1 |     9 |     6   (0)| 00:00:01 |
|*  4 |   FIXED TABLE FIXED INDEX| X$KTUQQRY (ind:1)      |     1 |  2498 |     0   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------

Outline Data
-------------

  /*+
      BEGIN_OUTLINE_DATA
      FULL(@"SEL$4" "X"@"SEL$4")
      USE_NL(@"SEL$62A6D27E" "X$KTUQQRY"@"SEL$3")
      LEADING(@"SEL$62A6D27E" "A"@"SEL$1" "X$KTUQQRY"@"SEL$3")
      FULL(@"SEL$62A6D27E" "X$KTUQQRY"@"SEL$3")
      NO_ACCESS(@"SEL$62A6D27E" "A"@"SEL$1")
      OUTLINE(@"SEL$3")
      OUTLINE(@"SEL$2")
      MERGE(@"SEL$3" >"SEL$2")
      OUTLINE(@"SEL$335DD26A")
      OUTLINE(@"SEL$1")
      MERGE(@"SEL$335DD26A" >"SEL$1")
      OUTLINE(@"SEL$5C160134")
      OUTLINE(@"SEL$5")
      MERGE(@"SEL$5C160134" >"SEL$5")
      OUTLINE_LEAF(@"SEL$62A6D27E")
      OUTLINE_LEAF(@"SEL$4")
      ALL_ROWS
      DB_VERSION('18.1.0')
      OPTIMIZER_FEATURES_ENABLE('18.1.0')
      IGNORE_OPTIM_EMBEDDED_HINTS
      END_OUTLINE_DATA
  */

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - filter("X"."ADVISORYID"=100511)
   4 - filter("XID"="A"."VERSIONS_XID" AND ("CON_ID"=0 OR "CON_ID"=3))

And in addition a couple of my scripts for fixed tables:

https://github.com/xtender/xt_scripts/blob/master/fixed_tables.sql

https://github.com/xtender/xt_scripts/blob/master/fixed_indexes.sql

Some time ago there was a question on the sql.ru about splitting validity periods for gym cards to enabled and blocked periods:

-- we have a table with gym cards (card id, validity period: from/to)
CREATE TABLE cards(id_card NUMBER, num_card VARCHAR2(100), dt_from DATE, dt_to DATE);
-- periods when cards were blocked (record id, card id, dates from/to)
CREATE TABLE blocks(id_block NUMBER, id_card NUMBER, dt_from DATE, dt_to DATE);
-- cards data:
INSERT INTO cards (id_card, num_card, dt_from, dt_to) VALUES (1,'111111', TO_DATE('01.09.2016','DD.MM.YYYY'), TO_DATE('01.09.2019','DD.MM.YYYY'));
INSERT INTO cards (id_card, num_card, dt_from, dt_to) VALUES (2,'222222', TO_DATE('06.10.2017','DD.MM.YYYY'), TO_DATE('31.12.2050','DD.MM.YYYY'));
INSERT INTO cards (id_card, num_card, dt_from, dt_to) VALUES (3,'333333', TO_DATE('09.05.2019','DD.MM.YYYY'), TO_DATE('31.12.2050','DD.MM.YYYY'));
-- blocks data:
INSERT INTO blocks (id_block, id_card, dt_from, dt_to) VALUES (101, 1, TO_DATE('20.03.2017','DD.MM.YYYY'), TO_DATE('09.04.2017','DD.MM.YYYY'));
INSERT INTO blocks (id_block, id_card, dt_from, dt_to) VALUES (102, 1, TO_DATE('14.01.2018','DD.MM.YYYY'), TO_DATE('03.02.2018','DD.MM.YYYY'));
INSERT INTO blocks (id_block, id_card, dt_from, dt_to) VALUES (103, 1, TO_DATE('18.02.2019','DD.MM.YYYY'), TO_DATE('10.03.2019','DD.MM.YYYY'));
INSERT INTO blocks (id_block, id_card, dt_from, dt_to) VALUES (201, 2, TO_DATE('02.08.2018','DD.MM.YYYY'), TO_DATE('10.11.2018','DD.MM.YYYY'));
COMMIT;

Just for fun, I’ve solved it using match_recognise:

with 
 cards (id_card, num_card, dt_from, dt_to) as (
   select 1,'111111', TO_DATE('01.09.2016','DD.MM.YYYY'), TO_DATE('01.09.2019','DD.MM.YYYY') from dual union all
   select 2,'222222', TO_DATE('06.10.2017','DD.MM.YYYY'), TO_DATE('31.12.2050','DD.MM.YYYY') from dual union all
   select 3,'333333', TO_DATE('09.05.2019','DD.MM.YYYY'), TO_DATE('31.12.2050','DD.MM.YYYY') from dual 
),blocks (id_block, id_card, dt_from, dt_to) as (
   select 101, 1, TO_DATE('20.03.2017','DD.MM.YYYY'), TO_DATE('09.04.2017','DD.MM.YYYY') from dual union all
   select 102, 1, TO_DATE('14.01.2018','DD.MM.YYYY'), TO_DATE('03.02.2018','DD.MM.YYYY') from dual union all
   select 103, 1, TO_DATE('18.02.2019','DD.MM.YYYY'), TO_DATE('10.03.2019','DD.MM.YYYY') from dual union all
   select 201, 2, TO_DATE('02.08.2018','DD.MM.YYYY'), TO_DATE('10.11.2018','DD.MM.YYYY') from dual
)
,data as (
   select *
   from (
         select * 
         from (
            select id_card,dt_from,dt_to,'c' t from cards
            union all
            select id_card,dt_to,dt_from,'b' from blocks
         ) v
         --where v.id_card=1 -- here we can filter card ID if needed
        ) piv
   unpivot(dt for x in (dt_from as 'dt_from', dt_to as 'dt_to'))
)
select * 
from data
match_recognize (
   partition by id_card
   order by dt /* we can modify add "t" into "order by clause" to make it more deterministic */
   measures
      match_number() as N,
      first(dt) as dt_from,
      last(dt) as dt_to
   pattern (x_start+ x_end)
   define
      x_start as x = 'dt_from'
     ,x_end   as x = 'dt_to'
);

Monthly Archives: June 2019

flashback_transaction_query: fixed table full table scan

SQL: Split periods