The problem of du Statistical File size

as mentioned, I found that the command

du -h
The file size obtained by

differs greatly from the actual file size, as shown in the following figure (the distribution version of linux is centos7)
screenshot 2019-01-20 afternoon 3.03.22.png
clipboard.png

test1 files actually use only 77 bytes, but 4.0k is counted with du-h. I don"t know why?
in addition, I would also like to ask if this 4.0k has any special meaning under linux? Because I see that many folders are 4.0kb after ll-h, but the size of these folders is not 4kb at all

May.09,2022

du shows the amount of disk space occupied by default. The folder itself has no physical content, but it also takes up a disk block (the smallest unit of the file system). The size of your file system is 4KB, so you will often see this number.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b319ed-2bda2.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b319ed-2bda2.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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