If I have a directory containing many files to be added for file monitoring inputs, Splunk reads the files one by one. It'll take a long time if the files have a big size. Is there any way Splunk can read multiple files simultaneously to improve the inputs speed(not with multiple forwarders, just for one Splunk instance or one Forwarder instance )? Thanks!
Not really, splunk indexers already go full speed by default.
Check your indexing queues queues with the sos app to find any bottleneck.
One remark about universal and lighweight forwarders : they have a limit of 256 kbps for the network speed. You can remove this limit.