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