If the database is shut down in an orderly fashion,
will not leak unused
preallocated values. Instead, any unused values will be thrown away, and the
sequence generator will continue where it left off once the database reboots.
However, if the database exits unexpectedly, the sequence generator will
skip the unused preallocated values when the database comes up again. This will
leave a gap between the last NEXT VALUE FOR (issued before the database exited
unexpectedly) and the next NEXT VALUE FOR (issued after the database
reboots).
Syntax
derby.language.sequence.preallocator=number
or
derby.language.sequence.preallocator=className
If set to a positive number, that is the number of values which
preallocates for each sequence. A higher value may improve the concurrency of
sequences.
If set to a class name, that class must implement
org.apache.derby.catalog.SequencePreallocator. The class
customizes the size of the preallocation range for each sequence. For more
information, see the public API documentation for
org.apache.derby.catalog.SequencePreallocator.
Default
100
By default,
preallocates 100 values for each sequence.
Example
derby.language.sequence.preallocator=125
Scope
system-wide,
database-wide
Dynamic or static
This property is semi-static; changing it while
is running
will not affect sequences which are already
being used. However, the new value will be picked up by sequences which weren't being used before the value was
changed. In addition, DDL causes the old value to be forgotten. After
performing DDL, the new value will be picked up by all sequences.