max concurrently recovered db determines the degree of parallelism. The minimum value is 1, but you can also use the default value of 0, directing Adaptive Server to use a self-tuning apparoach. The maximum value is the number of engines at startup minus 1. max concurrently recovered db is also limited by the value of the configuration parameter number of open databases.
The default value is 0, which indicates automatic self-tuning by the server to determine the appropriate number of recovery tasks. A value of 1 indicates serial recovery.
