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

The code doesn't seem to be working correctly.


(1)
+				for (block_num = 0; block_num <= nblocks; block_num++)

should be

+				for (block_num = firstDelBlock[fork_num]; block_num < nblocks; block_num++)

because:

* You only want to invalidate blocks >= firstDelBlock[fork_num], don't you?
* The relation's block number ranges from 0 to nblocks - 1.


(2)
+					INIT_BUFFERTAG(newTag, rnode.node, forkNum[fork_num],
+								   firstDelBlock[block_num]);

Replace firstDelBlock[fork_num] with block_num, because you want to process the current block of per-block loop.  Your code accesses memory out of the bounds of the array, and doesn't invalidate any buffer.


(3)
+					if (RelFileNodeEquals(bufHdr->tag.rnode, rnode.node) &&
+						bufHdr->tag.forkNum == forkNum[fork_num] &&
+						bufHdr->tag.blockNum >= firstDelBlock[block_num])
+						InvalidateBuffer(bufHdr);	/* releases spinlock */
+					else
+						UnlockBufHdr(bufHdr, buf_state);

Replace
bufHdr->tag.blockNum >= firstDelBlock[fork_num]
with
bufHdr->tag.blockNum == block_num
because you want to check if the found buffer is for the current block of the loop.


(4)
+				/*
+				 * We've invalidated the nblocks already. Scan the shared buffers
+				 * for each fork.
+				 */
+				if (block_num > nblocks)
+				{
+					DropRelFileNodeBuffersOfFork(rnode.node, forkNum[fork_num],
+												 firstDelBlock[fork_num]);
+				}

This part is unnecessary.  This invalidates all buffers that (2) failed to process, so the regression test succeeds.


Regards
Takayuki Tsunakawa