Shows the progress of "Updating" and allows output debugging log

[yfdyh000]

I want to find out why sometimes the update process consumes hundreds of seconds or more for 1500k files on HDD, and rebuild is done faster.

[void]

There are file system changes that occurred while Everything was not running.
When you launch Everything, Everything needs to read the USN Journals for the list of changes that occurred.
Everything has to go to disk for this information which is slow. (If Everything is running this information is usually cached by the OS).
Renaming folders is expensive in Everything (every subfolder and subfile needs to be reinserted into the database). Usually a folder rename takes less than a second. However, if you rename 1000+ this can add up..

Updating the database can take longer than a full rebuild when:

• There is more changes to your disk than there are files on your disk. (Windows updates, changing attributes to every file)
• There are many folder renames. (10,000+)
• Retrieving file information out of sequence might be slow. A rebuild will read all file information in sequence and is generally faster.

Please try starting Everything in debug mode:
Everything.exe -debug

This will start Everything with a debug console that will log what Everything is doing during startup.
Look for Cyan colored lines starting with USN. These are the updates that Everything is currently processing.