Write Ahead FlowFile Repository

WriteAheadFlowFileRepository is the default implementation. It persists FlowFiles to disk, and can optionally be configured to synchronize all changes to disk. This is very expensive and can significantly reduce NiFi performance. However, if it is false, there could be the potential for data loss if either there is a sudden power loss or the operating system crashes. The default value is false.


Property	Description
`nifi.flowfile.repository.wal.implementation`	If the repository implementation is configured to use the `WriteAheadFlowFileRepository`, this property can be used to specify which implementation of the Write-Ahead Log should be used. The default value is `org.apache.nifi.wali.SequentialAccessWriteAheadLog`. This version of the write-ahead log was added in version 1.6.0 of Apache NiFi and was developed in order to address an issue that exists in the older implementation. In the event of power loss or an operating system crash, the old implementation was susceptible to recovering FlowFiles incorrectly. This could potentially lead to the wrong attributes or content being assigned to a FlowFile upon restart, following the power loss or OS crash. However, one can still choose to opt into using the previous implementation and accept that risk, if desired (for example, if the new implementation were to exhibit some unexpected error). To do so, set the value of this property to `org.wali.MinimalLockingWriteAheadLog`. Another available implementation is `org.apache.nifi.wali.EncryptedSequentialAccessWriteAheadLog`. If the value of this property is changed, upon restart, NiFi will still recover the records written using the previously configured repository and delete the files written by the previously configured implementation.
`nifi.flowfile.repository.directory`*	The location of the FlowFile Repository. The default value is `./flowfile_repository`.
`nifi.flowfile.repository.checkpoint.interval`	The FlowFile Repository checkpoint interval. The default value is `2 mins`.
`nifi.flowfile.repository.always.sync`	If set to `true`, any change to the repository will be synchronized to the disk, meaning that NiFi will ask the operating system not to cache the information. This is very expensive and can significantly reduce NiFi performance. However, if it is `false`, there could be the potential for data loss if either there is a sudden power loss or the operating system crashes. The default value is `false`.