Setting Transmit Durability on DATASTORE Element
A master database configured for asynchronous or return receipt replication is durable
by default. This means that log records are committed to the file system when transactions are
committed. The master database can be set to nondurable by including the TRANSMIT
NONDURABLE
clause in the element description.
Transaction records in the master database log buffer are, by default, flushed to the file system before they are forwarded to subscribers. If the entire master database is replicated (ELEMENT
is of type DATASTORE
), you can improve replication performance by eliminating the master's flush-log-to-disk operation from the replication cycle. This is done by including a TRANSMIT NONDURABLE
clause in the element description. The TRANSMIT
setting has no effect on the subscriber. The transaction records on the subscriber database are always flushed to the file system.
Master databases configured for return twosafe replication are nondurable by default and cannot be made durable. Setting TRANSMIT DURABLE
on a database that is configured for return twosafe replication has no effect on return twosafe transactions.
For example, you can replicate the entire contents of the master database (masterds
) to the subscriber database (subscriberds
) and eliminate the flush-log-to-disk operation by using TRANSMIT
NONDURABLE
. Your element description (named a
) might look like the following:
ELEMENT a DATASTORE MASTER masterds ON "system1" TRANSMIT NONDURABLE SUBSCRIBER subscriberds ON "system2"
In general, if a master database fails, you have to initiate the
ttRepAdmin
-duplicate
operation described in Recovering a Failed Database
to recover the failed master from the subscriber database. This is always true for a master
database configured with TRANSMIT DURABLE
.
A database configured as TRANSMIT NONDURABLE
is recovered
automatically by the subscriber replication agent if it is configured in the specific type of
bidirectional scheme described in Automatic Catch-Up of a Failed Master Database. Otherwise, you must follow the procedures
described in Recovering Nondurable Databases to recover a failed nondurable database.