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• have_symlink 

YES  if symbolic link support is enabled, NO  if not. This is required on Unix for support of the DATA DIRECTORY  and INDEX DIRECTORY  table options. If the server is started with the --skip-symbolic- links  option, the value is DISABLED . 

This variable has no meaning on Windows. 

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• histogram_generation_max_mem_size 

## Note 

Symbolic link support, along with the --symbolic-links  option that controls it, is deprecated; expect these to be removed in a future version of MySQL. In addition, the option is disabled by default. The related have_symlink  system variable also is deprecated and you should expect it to be removed in a future version of MySQL. 

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The maximum amount of memory available for generating histogram statistics. See Section 8.9.6, “Optimizer Statistics” , and Section 13.7.3.1, “ANALYZE TABLE Statement” . 

Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges” . 

• host_cache_size 

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