What to do before RBA or LRSN limits are reached

Before a Db2 subsystem or data sharing group reaches the end of the log RBA range, you must reset the log RBA value. The process that you use to reset the log RBA value depends on whether the Db2 subsystem is a member of a data sharing group or in a non-data sharing environment.

About this task

The log limits are expressed as RBA values in non-data-sharing environments and as LRSN timestamps in data-sharing environments. Approximately one year before the end of the LRSN is reached, message DSNJ034I is issued to inform you that the LRSN is approaching the log limit. Contact IBM® Support if this happens.

The log RBA is an ever-increasing 10-byte hexadecimal value. The maximum value is 2**80 (x'FFFFFFFFFFFFFFFFFFFF').

The rate at which the log RBA value increases through this range depends on the logging rate of the Db2 subsystem. When a heavy logging rate is sustained over a period of years, the log RBA value can begin to approach the end of the range.

When the logs are in 10-byte format, page sets can be in 6-byte format or 10-byte format, depending on whether the page sets have been converted to extended format. If the page sets have not been converted to extended format, two logging limits affect processing:

Soft limit
The soft limit occurs at RBA x'00000000FFF800000000' or at an LRSN approximately two months before the 6-byte capacity is reached. When the soft limit is reached, user objects in basic 6-byte format are restricted to read-only access. Attempts to update those objects are rejected. If you need to update table spaces and indexes that have reached the soft limit, you can convert them to extended 10-byte page format. Ensure that all catalog and directory page sets are converted to extended format. Utilities that open an output object as unrecoverable can still run after the soft limit is reached. If the output object will be in extended format, such as for a REORG that converts from basic to extended format, the utility can run successfully.
Attention: In a non-data sharing environment, failure to convert page sets to the 10-byte RBA format before the 6-byte logging limit is reached results in failed updates with reason code 00C2026D. No updates are allowed for any object that is still in basic format. It is strongly recommended that the catalog and directory table spaces be converted immediately following the conversion of the BSDS to the 10-byte format. All other objects need to be converted to extended format before the logging limit is reached in order to avoid outages.

In a data sharing environment, page sets contain LRSNs instead of RBAs. After the BSDS has been converted to allow for 10-byte LRSNs, an LRSN that is greater than 6 bytes does not result in failed updates with reason code 00C2026D. It is recommended that after the BSDS has been converted, the catalog and directory table spaces are converted before any other objects. Other objects need to be converted to extended format before the LRSN value reaches the 6-byte LRSN limit.

Hard limit
The hard limit is the actual limit, and occurs when the RBA or LRSN no longer fits in 6 bytes. That value is x'00000000FFFFFFFFFFFF' for an RBA, and x'00FFFFFFFFFFFFFFFFFF' for an LRSN. When the actual limit is reached, you cannot update objects that are in basic format. Attempts to update an object that is in basic format are rejected. When the hard limit has been reached, no online utilities can run if catalog and directory page sets are not in extended format.
Important: If the RBA for a non data sharing Db2 subsystem reaches or exceeds the hard or soft limit, you must either convert all table spaces and indexes to the 10-byte format or use the RBA reset procedure. Enabling data sharing is not sufficient to resolve the problem.

Db2 might issue message DSNB233I to remind you to convert page sets to the 10-byte format.

Procedure

  1. Determine when the 10-byte RBA and LRSN limits are likely to be reached by using one of the following methods:
    • Message DSNJ032I is issued at the active log switch when the RBA threshold is reached for the 10-byte format. If the RBA exceeds x'FFFFFFFF000000000000', the message is issued with the keyword WARNING, and processing continues. If the RBA exceeds x'FFFFFFFFFF0000000000', the message is issued with the keyword CRITICAL, and Db2 stops. To resolve any outstanding units of work, Db2 restarts automatically in restart-light mode. Then Db2 stops again. In this situation, you can restart Db2 in ACCESS(MAINT) mode.

    • Calculate how much space is left in the log. You can use the print log map (DSNJU004) utility to obtain the highest written RBA value in the log. Subtract this RBA from x'FFFFFFFFFFFFFFFFFFFF' to determine how much space is left in the log.

      You can use the output from the print log map utility to determine how many archive logs are created on an average day. This number multiplied by the RBA range of the archive log data sets (ENDRBA minus STARTRBA) provides the average number of bytes that are logged per day. Divide this value into the space remaining in the log to determine approximately how much time is left before the end of the log RBA range is reached. If there is less than one year remaining before the end of the log RBA range is reached, start planning to reset the log RBA value. If less than three months remain before the end of the log RBA range is reached, you need to take immediate action to reset the log RBA value.

  2. Monitor the log for RBAs that reach the 6-byte soft and hard RBA limits.
    You need to do this if any page sets still use the basic 6-byte format.
    1. Calculate how much space is left in the log. You can use the print log map (DSNJU004) utility to obtain the highest written RBA value in the log. To determine the amount of space that is left until you reach the soft limit, subtract the highest written RBA from the soft limit of x'00000000FFF800000000'. To determine the amount of space that is left before you reach the hard limit, subtract the highest written RBA from the hard limit of x'00000000FFFFFFFFFFFF'.
    2. Convert page sets to use the extended 10-byte format.
      Important: In particular, you need to convert all catalog and directory page sets to extended format as soon as possible. When the hard limit is reached, it might not be possible to convert the catalog and directory.

      For information on how to convert page sets to extended format, see Converting page sets to the 10-byte RBA or LRSN format.