What Are Histsize, Histfilesize, Histsize in Linux

All of these are shell enviroment varibales that determines the location and size of your current shell history.
HISTFILE
Indicates the history file, that stores your shell commands.
SAVEHIST (HISTFILESIZE)
Indicates the size of your history file, meaning how many command/events it can store. By defauat zsh
only sets in to 30, while not setting the HITFILE
at all, meaning no history is persisted.
HISTSIZE
Indicates the size of your current history session; how many commands from your history file can be loaded into your shell's memory in a session.