APAR status
Closed as program error.
Error description
When the execution of a query involves the scan of an index in the reverse direction some additional precautions are necessary to ensure that execution does not become deadlocked with other threads using the index in the forward direction. These precautions include a back-off and retry mechanism which may include the need to access many index pages. If there are large numbers of index pages containing only deleted entries then the number of pages needing to be accessed will increase which can increase the chances of triggering the retry mechanism. Here is an example query plan showing a reverse index scan: select max(id) as max_id from tab1 where from_time + 10 units second < CURRENT Estimated Cost: 2 Estimated # of Rows Returned: 1 1) informix.tab1: INDEX PATH Filters: informix.tab1.from_time + interval(10) second(9) to second < CURRENT year to fraction(3) (1) Index Name: informix.itab1_x1 Index Keys: id (Reverse) (Aggregate) (Serial, fragments: ALL) Factors to consider to help avoid the problem include monitoring of btscanner activity to remove deleted entries from the index and creation of an index defined using a descending order on the column(s).
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: * * Users of Informix Server prior to 12.10.xC16 and 14.10.xC7. * **************************************************************** * PROBLEM DESCRIPTION: * * See Error Description * **************************************************************** * RECOMMENDATION: * * Upgrade to Informix Server 12.10.xC16Â or 14.10.xC7. * ****************************************************************
Problem conclusion
Fixed in Informix Server 12.10.xC16 and 14.10.xC7.
Temporary fix
Comments
APAR Information
APAR number
IT37120
Reported component name
INFORMIX SERVER
Reported component ID
5725A3900
Reported release
C10
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2021-06-03
Closed date
2021-11-02
Last modified date
2023-05-02
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
[{"Business Unit":{"code":"BU059","label":"IBM Software w\/o TPS"},"Product":{"code":"SSGU8G","label":"Informix Servers"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"C10","Line of Business":{"code":"LOB10","label":"Data and AI"}}]
Document Information
Modified date:
03 May 2023