What are the pitfalls of using "Preserve" for Cursor Behavior in Informix ODBC DSN?
Based on the research below, I feel confident that I can recommend to change the Cursor Behavior to Preserve, though at a potential performance hit.  I believe the performance loss with Preserve is minimal compared to the potential performance hit on a large recordset with code that performs a .MoveLast/.MoveFirst to populate the recordset.



Useless info From IBM:
Flag for cursor behavior when a commit or rollback transaction is called
Possible values are:
•   0=close cursor
•   1=preserve cursor
https://www.ibm.com/support/knowledgecenter/en/SSGU8G_11.70.0/com.ibm.odbc.doc/ids_odbc_069.htm

Performance risks From DataDirect for ODBC:
Purpose
Determines whether cursors will be preserved or closed at the end of transactions.
Valid Values
0 | 1
Behavior
If set to 1 (Enabled), cursors are held at their current position when transactions end. This value may slow the performance of your database operations.
If set to set to 0 (Disabled), cursors are closed at the end of transactions.

http://media.datadirect.com/download/docs/odbc/allodbc/index.html#page/odbc/cursor-behavior.html

Performance risks From Pace University for connecting to Informix for administering ColdFusion Server:
Preserve cursors at the end of each transaction -- Determines whether cursors will be preserved or closed at the end of each transaction. Enable this attribute if you want cursors to be held at the current position when the transaction ends. Enabling this option may impact the performance of your database operations.
http://csis.pace.edu/~ctappert/cs615-02/support/Help/Administering_ColdFusion_Server/admin0416.htm

Required Preserve For ArcGIS (popular software):
Cursor Behavior must be set to 1 - Preserve because ArcGIS expects Informix cursors to remain open and active following a database COMMIT operation.
Setting the Cursor Behavior to 0 - Close will have undesirable effects during data insertions and updates.
http://desktop.arcgis.com/en/arcmap/10.3/manage-data/gdbs-in-informix/set-odbc-informix.htm

Required Preserve For TOTVS DBACCESS (unknown software):
… determines the behavior of the database in relation to the automatic closing of cursors when instructions COMMIT WORK or ROLLBACK WORK are submitted.
If the configuration is not proper [during Fetch operations], Cursors may return EOF before the end of data recovery

http://tdn.totvs.com/display/tecen/DBAccess+-+Informix+-+ODBC+-+Cursor+Behavior