As previously noted, by default transaction commits are durable because they cause the modifications performed under the transaction to be synchronously recorded in your on-disk log files. However, it is possible to use non-durable transactions.
You may want non-durable transactions for performance reasons. For example, you might be using transactions simply for the isolation guarantee. In this case, you might not want a durability guarantee and so you may want to prevent the disk I/O that normally accompanies a transaction commit.
There are several ways to remove the durability guarantee for your transactions:
Specify
true to the
EnvironmentConfig.setTxnNoSync()
method.
This causes DB to not synchronously force any log
data to disk upon transaction commit. That is, the modifications are held entirely
in the in-memory cache and the logging information is not forced to the filesystem for
long-term storage.
Note, however, that the logging
data will eventually make it to the filesystem (assuming no
application or OS crashes) as a part of DB's
management of its logging buffers and/or cache.
This form of a commit provides a weak durability guarantee because data loss can occur due to an application, JVM, or OS crash.
This behavior is specified on a per-environment handle basis. In order for your application to exhibit consistent behavior, you need to specify this method for all of the environment handles used in your application.
You can achieve this behavior on a transaction by transaction basis by
using Transaction.commitNoSync()
to commit your transaction, or by specifying true to the
TransactionConfig.setNoSync() method when starting the
transaction.
Specify
true to the
EnvironmentConfig.setTxnWriteNoSync()
method.
This causes
logging
data to be synchronously
written to the OS's file system buffers upon
transaction commit. The data will eventually be
written to disk, but this occurs when the
operating system chooses to schedule the
activity; the transaction commit can complete
successfully before this disk I/O is performed
by the OS.
This form of commit protects you against application
and JVM crashes, but not against OS
crashes. This method offers less room for the possibility of data loss than does
EnvironmentConfig.setTxnNoSync().
This behavior is specified on a per-environment handle basis. In order for your application to exhibit consistent behavior, you need to specify this method for all of the environment handles used in your application.
You can achieve this behavior on a transaction by transaction basis by
using Transaction.commitWriteNoSync()
to commit your transaction, or by specifying true to
TransactionConfig.setWriteNoSync() method when starting the
transaction.
Maintain your logs entirely in-memory. In this case, your logs are never written to disk. The result is that you lose all durability guarantees. See Configuring In-Memory Logging for more information.