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          
                        
                            DB_TXN_NOSYNC using the
                            
                            DbEnv::set_flags()
                        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 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 flag for all of the environment handles used in your application.
                    You can achieve this behavior on a transaction by transaction basis by
                        
                            specifying DB_TXN_NOSYNC to the
                                
                                DbTxn::commit()
                                
                            method.
                        
                        
                
                    Specify
                    
                        DB_TXN_WRITE_NOSYNC using the
                            
                            DbEnv::set_flags()
                        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
                             crashes, but not against OS
                            crashes.  This method offers less room for the possibility of data loss than does
                            DB_TXN_NOSYNC.
                            
                
This behavior is specified on a per-environment handle basis. In order for your application to exhibit consistent behavior, you need to specify this flag for all of the environment handles used in your application.
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.