help:how to write a planner_hook and other hooks in pg

<div class="Section1" style="layout-grid:15.6pt"><p class="MsoNormal"><font face="Arial" size="1"><span lang="EN-US"
style="font-size:
9.0pt;font-family:Arial">Hi all:</span></font><p class="MsoNormal"><font face="Arial" size="1"><span lang="EN-US"
style="font-size:
9.0pt;font-family:Arial">I am doing some experiments programming on PG. I tried to modify planner and I find the
‘planner_hook’in source code, but I don’t know how to use it.</span></font><p class="MsoNormal"><font face="Arial"
size="1"><spanlang="EN-US" style="font-size: 
9.0pt;font-family:Arial">Anybody knows? If any code sample, very precious.</span></font><p class="MsoNormal"><font
face="Arial"size="1"><span lang="EN-US" style="font-size: 
9.0pt;font-family:Arial">Thanks</span></font><p class="MsoNormal"><font face="Arial" size="1"><span lang="EN-US"
style="font-size:
9.0pt;font-family:Arial"> </span></font><p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><fontface="宋体" size="2"><span
style="font-size:10.5pt;font-family:宋体">张茂森</span></font><spanlang="EN-US"> ZhangMaosen</span><p
class="MsoNormal"><fontface="Times New Roman" size="2"><span lang="EN-US"> </span></font></div>