INFORMIX SERVER / 5725A3900 / B70 - IDS 11.70

Consider following query, finding the last existing date value
in a given year:

 select max(date_column) from my_table where year(date_column) =
2018;

If an index exists having 'date_column' as only or leading
field, you'll see a reverse aggregate key-only scan on such
index scanning exactly as many index entries (not keys) as there
are above the 'index key filter'.

  1) owner.my_table: INDEX PATH

    (1) Index Name: owner.date_ix
        Index Keys: dt c i   (Key-Only) (Reverse)  (Aggregate)
(Serial, fragments: ALL)
        Index Key Filters:  (YEAR (owner.my_table.date_column )
= 2018 )

Query statistics will show as many rows scanned ('rows_scan'),
as there exist rows (not key values) for years greater than
2018, duration can be considerable.

This was found to be the cause behind recurring
"listener-thread: err = -25582: oserr = 0" connection failures
(and succeeding connections being delayed simultaneously), as a
consequence of such scan potentially extensively blocking an
entire vp.

****************************************************************
* USERS AFFECTED:                                              *
* Users of IDS version prior to 11.70.xC10.                    *
****************************************************************
* PROBLEM DESCRIPTION:                                         *
* QUERYING MAXIMUM VALUE OUT OF A GIVEN RANGE IN A DATE COLUMN *
* WILL SCAN INDEX FROM END WITHOUT YIELDING VP                 *
****************************************************************
* RECOMMENDATION:                                              *
****************************************************************

Semantically identical query 'select max(date_column) from
my_table where date_column

not known / see Local fix

Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :

06.05.2019
26.09.2019
31.08.2020