RE: [Patch] Optimize dropping of relation buffers using dlist

From: Jamison, Kirk/ジャミソン カーク <k.jamison@fujitsu.com>
> Apologies for the delay, but attached are the updated versions to simplify the
> patches.

Looks good for me.  Thanks to Horiguchi-san and Andres-san, the code bebecame further compact and easier to read.  I've
markedthis ready for committer. 


To the committer:
I don't think it's necessary to refer to COMMIT/ROLLBACK PREPARED in the following part of the 0003 commit message.
Theysurely call DropRelFileNodesAllBuffers(), but COMMIT/ROLLBACK also call it. 

the full scan threshold. This improves the DropRelationFiles()
performance when the TRUNCATE command truncated off any of the empty
pages at the end of relation, and when dropping relation buffers if a
commit/rollback transaction has been prepared in FinishPreparedTransaction().


Regards
Takayuki Tsunakawa