CHECKPOINT
Forces the
system to take a checkpoint.
SYNTAX
DESCRIPTION
The CHECKPOINT
command forces DBMaker to take a checkpoint. You may want to take a checkpoint
if database activity is very high and you infrequently back up or restart
your database. To execute the CHECKPOINT command, you must have DBA or
SYSADM security privileges.
A checkpoint
is a system event in which the database is brought to a clean state. DBMaker
writes all journal records and all dirty data pages in memory buffers
to disk, and reclaims journal blocks that are no longer required for backup
or recovery purposes. DBMaker can reclaim journal blocks that contain
non-active transactions that completed before the start of the oldest
active transaction.
Startup
time after an instance failure is reduced after taking a checkpoint. DBMaker
writes the time of the last checkpoint and a list of all transactions
active at the time of the checkpoint to the journal file header. During
database recovery, DBMaker uses this information to determine which transactions
should be undone, which should be redone, and which should be ignored.
DBMaker
will automatically take a checkpoint when a database starts or terminates,
when you perform an online backup, or when the journal is full. This may
require a significant amount of time to complete, depending on the size
and number of transactions since the last checkpoint. Any transactions
that are active when an automatic checkpoint occurs must wait until the
checkpoint operation completes. DBMaker will also abort the current transaction
if the journal is full and issuing a checkpoint cannot reclaim enough
space to complete the transaction. In this situation, you must redo all
commands in the aborted transaction.
To avoid
any unnecessary delay in transaction processing, you should periodically
take manual checkpoints using the CHECKPOINT command. Periodic manual
checkpoints reduce the amount of time required to start, terminate, and
back up a database, the amount of time transactions must wait for individual
checkpoint operations to complete, and the possibility that you will encounter
a full journal. The optimal time interval between manual checkpoints depends
on the frequency of activity in the database.
EXAMPLE
The following
example forces the system to take a checkpoint.
RELATED
COMMANDS
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