IT27689: IF XYUNITS IN SPATIAL_REFERENCES TABLE IS SET TOO LARGE, SPATIALINDEXES CAN BE IGNORED WHEN DISTRIBUTIONS ARE BUILT

APAR status

• Closed as program error.

Error description

• Consider the following example:
  
  create table t1 (col1 int, col2 st_geometry);
  
  create index idx1 on t1(col2 st_geometry_ops) using rtree;
  
  If the xyunits column of the included spatial reference system
  with SRID == 4 is modified to increase it's value with the
  following SQL statement:
  
  update spatial_references
  set xyunits = 596523200
  where srid = 4;
  
  If you then load data to the table and run update statistics
  high and/or medium and try and run the following query with set
  explain on, you would see the server pick a sequential scan,
  rather then using the index on the spatial column, col2.
  
  If the distributions on the spatial column are dropped, the
  query will go back to using the spatial index.
  
  example query:
  
  select count(*) from t1
  where
  informix.SE_EnvelopesIntersect(col2,ST_PolyFromText('POLYGON
  ((-43.4274583345408 -22.4553006230988, -43.4274583345408
  -22.4482426104252, -43.4105975264892 -22.4482426104252,
  -43.4105975264892 -22.4553006230988, -43.4274583345408
  -22.4553006230988))' , 4 ) );
  
  
  Bad set explain output showing sequential scan:
  
  Estimated Cost: 34001
  Estimated # of Rows Returned: 1
  
    1) informix.t1: SEQUENTIAL SCAN
  
          Filters: informix.se_envelopesintersect(informix.t1.col2
  ,UDT )
  
  If the xyunits value is not modified and left with it's default
  the query would use the index and the set explain output would
  look like this:
  
  Estimated Cost: 1
  Estimated # of Rows Returned: 1
  
    1) informix.t1: INDEX PATH
  
      (1) Index Name: informix.t1_idx1
          VII Index Keys: col2   (Serial, fragments: ALL)
          VII Index Filter:
  informix.se_envelopesintersect(informix.t1.col2,UDT )
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Users of IDS prior to 12.10.xC13.                            *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * When xyunits value in spatial_references table gets too      *
  * large, indexes on spatial columns may not get used when      *
  * distributions are built on that column.                      *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  

Problem conclusion

• Fixed in IDS 12.10.xC13.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  INFORMIX SERVER

• Fixed component ID

  5725A3900

Applicable component levels