There is a file with a vast amount of old data.

IgnoreOlderThan:This setting filters files for indexing based on their age. It does not prevent indexing of old data already in the file.

allowList:This setting allows specifying patterns to include files for monitoring, but it does not control indexing of pre-existing data.

monitor:This is the default method for monitoring files but does not address indexing pre-existing data.

followTail:This attribute, when set in inputs.conf, ensures that Splunk starts reading a file from the end (tail) and does not index existing old data. It is ideal for scenarios with large files where only new updates are relevant.