Allow WAL information to recover corrupted pg_controldata - Mailing list pgsql-hackers

<div class="WordSection1"><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">I am
planningto work on the below Todo list item for this CommitFest</span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">AllowWAL information to recover corrupted pg_controldata
</span><br/><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><a
href="http://archives.postgresql.org/pgsql-patches/2006-06/msg00025.php">http://archives.postgresql.org/pgsql-patches/2006-06/msg00025.php</a></span><br
/><spanstyle="font-size:10.0pt;font-family:"Arial","sans-serif"">   </span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Iwanted to confirm my understanding about the work involved
forthis patch:</span><br /><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">The existing patch has
followingset of problems:</span><br /><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">   1. Memory leak
andlinked list code path is not proper</span><br /><span style="font-size:10.0pt;font-family:"Arial","sans-serif""> 
 2.lock check for if the server is already running, is removed in patch which needs to be reverted</span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">  3. Refactoring of the code.</span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">  </span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Apartfrom above what I understood from the patch is that its
intentionis to generate values for ControlFile using WAL logs when -r option is used.</span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">  </span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Thechange in algorithm from current will be if control file
iscorrupt which</span> <span style="font-size:10.0pt;font-family:"Arial","sans-serif"">essentialy means
ReadControlFile()will return False, then it should</span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">generatevalues (checkPointCopy, checkPoint, prevCheckPoint,
state)using WAL if -r option is enabled.</span><p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Alsofor -r option, it doesn't need to call function
FindEndOfXLOG()as the that work will be achieved</span> <span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">byabove point. </span><p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Itwill just rewrite the control file and don’t do other
resets.</span><br/><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">   </span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif""> </span><br/><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Thealgorithm of restoring the pg_control value from old xlog
file:</span><br/><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">   1. Retrieve all of the active xlog
filesfrom xlog direcotry into a list by increasing order, according their timeline, log id, segment id.</span><br
/><spanstyle="font-size:10.0pt;font-family:"Arial","sans-serif"">   2. Search the list to find the oldest xlog file of
thelastest time line.</span><br /><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">   3. Search the
recordsfrom the oldest xlog file of latest time line</span> <span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">tothe latest xlog file of latest time line, if the checkpoint
record</span><br/><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">      has been found, update the
latestcheckpoint and previous checkpoint.</span><p class="MsoNormal"> <p class="MsoNormal">Apart from above some
changesin code will be required after the Xlog patch by Heikki.<br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">     </span><br /><span
style="font-size:10.0pt;font-family:"Arial","sans-serif"">Suggestme if my understanding is correct?</span><p
class="MsoNormal"> <pclass="MsoNormal"> <p class="MsoNormal"> </div>