The RecoveryLogSyncMode parameter controls how the Recovery Log is synchronized across Unity servers. The parameter default value is async. You can change the parameter to: near-sync or sync.
For near-sync, the Active Sequencer waits for all entries to be written to the Recovery Log of the Standby Sequencer before it sends the writes to the Teradata Database system. Performance impact for this operation depends on the network latency between the two Unity servers. In this mode, the operating system periodically writes to the Recovery Log cache on the Standby Sequencer, and writes to the disk. If both Unity servers fail at the same time, the Recovery Log on the Standby Sequencer might be missing entries, because the writes were not flushed to the disk.
For sync, the Standby Sequencer pushes all writes to the disk before responding to the Active Sequencer. This mode has the most data protection and the largest performance impact.
For near-sync or sync, the RecoveryLogSyncTimeout parameter specifies the maximum amount of time the Active Sequencer waits for a response from the Standby Sequencer before continuing. If the Active Sequencer does not receive a response from the Standby Sequencer, it continues sending requests to the Teradata Database systems. If the RecoveryLogSyncTimeout is set to 0 , then the Active Sequencer waits indefinitely for a response. Setting this parameter to 0 is not recommended.
Unity creates the Recovery Log when the Sequencer process starts. The RecoveryLogFullyCreate parameter determines the space allocation for the Recovery Log file on startup. The parameter can be set to one of the following values: true or false.
If true, this parameter does not result in a sparse file; space is allocated on initial startup. Startup time for the Sequencer increases the first time the Sequencer is started; startup time is not impacted for the subsequent restarts of the Sequencer. This also guarantees that there is sufficient space available for the Recovery Log and Writes will not fail due to out-of-disk errors. Use to ensure sufficient space for the Recovery Log.
If false, this parameter results in a sparse file; space is allocated for the Recovery Log as it receives data Writes. Use when there is sufficient disk space for the Recovery Log and another process is not using the disk space to enable faster process startup. This does not impact the Sequencer process startup time. Unity only detects insufficient disk space for the entire Recovery Log during operation, resulting in a fatal error.