Thanks a lot. 

oops, indeed, the clean up stage is not in the XLog replay, So there is no 



发件人: Tom Lane 
发送时间: 2012-07-18  10:05:26 
收件人: xu2002261 
抄送: pgsql-hackers 
主题: Re: [HACKERS] During Xlog replaying, is there maybe emitted xlog? 
"xu2002261" <> writes:
> Hi all,
>      I reviewed the source code, and saw the following calling path:
>      StartupXLOG() > StartupDatabase() > RmgrTable[rmid].rm_cleanup() > 
> btree_xlog_cleanup() > _bt_insert_parent > _bt_insertonpg() > XLogInsert()
> As we can see, during xlog replaying, XLog may be emitted. So whether there 
> are some *ISSUE* in above calling stack?
No, it's entirely correct.  That path isn't "during" replay, it's upon
completion of replay, where we're cleaning up anything that failed to be
completed before the crash.  Emitting more WAL is allowed then.  Note
the comment a few lines above the rm_cleanup calls:
 * Resource managers might need to write WAL records, eg, to record
 * index cleanup actions.  So temporarily enable XLogInsertAllowed in
 * this process only.
regards, tom lane

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