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Informix - Problem description

Problem IT32532 Status: Closed

QUERY PLAN WITH BEST ESTIMATED COST THAT ALSO RUNS THE QUICKEST IS NOT
CHOSEN

product:
INFORMIX SERVER / 5725A3900 / B70 - IDS 11.70
Problem description:
Consider the following query (tab1 is a temp table)

select distinct
    tab2.c1,
    tab2.sn,
    tab2.c2||" "||tab2.c3||":"||tab2.c4||" "||
    tab2.c5 as OUT1,
    tab2.c15,
    t.c14t * t.c8 / abs(t.c8) OUT2,
    t.c13 * t.c8 / abs(t.c8) OUT3,
    case when (tc.tc10='S') then tab2.c6 else sd.c9 end as OUT4,
    tc.c12,
    tab1.c11,
    tc.c10
from
    tab1, tab2, tab3 t, tab4 tc, outer tab5 sd
where
    tab2.c7 = t.c7 and
    tc.c7 = t.c7 and
    tab2.c1 = t.c1 and
    tab1.c1 = tab2.c1 and
    tab2.c1 = sd.c1 and
    t.c8  "0"
into temp
    tran_n_p;

Query plan 1:

    DIRECTIVES FOLLOWED:
    INDEX ( tab2 tab2_idx03 )

    Estimated Cost: 348628

    Query time: 28 seconds

Query plan 2:

    DIRECTIVES FOLLOWED:
    INDEX ( tab2 tab2_idx06 )

    Estimated Cost: 8141022

    Query time: 18 seconds

The optimizer choses Query plan 1 above, HOWEVER, there is
another query plan that is not chosen that has the best
Estimated Cost and query time:

    DIRECTIVES FOLLOWED:
    INDEX ( tab2 tab2_idx06 )
    AVOID_HASH ( tab2 )

    Estimated Cost: 5108

    Query time: 10 seconds

Note: In a system with much more data, the query times are
significantly longer for the query plans with the higher
estimated costs.
Problem Summary:
****************************************************************
* USERS AFFECTED:                                              *
* Users of Informix Server prior to 11.70.FC9W2, 12.10.xC15    *
* and 14.10.xC5.                                               *
****************************************************************
* PROBLEM DESCRIPTION:                                         *
* See Error Description                                        *
****************************************************************
* RECOMMENDATION:                                              *
* Upgrade to Informix Server 11.70.xC9W2, 12.10.xC15 (when     *
* available) or 14.10.xC5.                                     *
****************************************************************
Local Fix:
Solution
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
12.04.2020
21.12.2020
21.12.2020
Problem solved at the following versions (IBM BugInfos)
Problem solved according to the fixlist(s) of the following version(s)
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