SQL/MX 3.2.1 Reference Manual (H06.26+, J06.15+)

SQL/MX Statements
HP NonStop SQL/MX Release 3.2.1 Reference Manual—691117-005
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Considerations for MODIFY
You can temporarily increase the TMF time limit and the size of the audit trail to allow
the operations to complete with a larger num-of-rows. However, increasing TMF
limits degrades system performance and increases disk space usage for the audit trail.
Default Value for Online Partition Operations
For online partition operations, avoid choosing a value greater than 500, because DP2
escalates locking from selected rows to the entire partition if the partition has more
than 511 row and file locks.
Concurrency and Timeout Considerations
When you use MODIFY, avoid long-running concurrent transactions on the same
object. Concurrency issues arise in two phases: during the data movement phase and
during the commit phase.
During the data movement phase, if MODIFY is writing to an existing partition,
MODIFY obtains row locks on data as it is written. If a concurrent application is also
writing to the same partition, contention can occur. Either MODIFY or the application
might experience timeouts if they each seek to access a row the other has locked. This
situation is especially true if the application holds so many locks that DP2 attempts to
escalate to a file lock or if the application transaction is long-running. If MODIFY times
out, the command is terminated.
During the commit phase, MODIFY attempts to obtain exclusive locks on all partitions
to update file labels. Again, if concurrent applications hold locks for long durations,
MODIFY times out in its attempt, and the MODIFY command fails.
Rename
The Guardian rename operation affects the file labels and the metadata. TMF recovery
is limited after the rename operation is performed. Rename of a location invalidates
TMF online dumps of that location (data fork and RFork). File recovery cannot cross a
rename operation.
TMF backout and volume recovery are both fully supported after the rename
operations are performed.
MODIFY and RDF
Rename
RDF does not replicate the file label changes occurred due to Guardian rename
operations on the SQL/MX objects. You must perform corresponding rename
operations on the backup system to synchronize primary and backup systems. You
Note. To retain recoverability, HP recommends making new TMF online dumps, immediately
after a Guardian rename operation is performed.