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

[k.jami...@fujitsu.com]

On Monday, September 28, 2020 5:08 PM, Tsunakawa-san wrote:

>       From: Jamison, Kirk/ジャミソン カーク <k.jami...@fujitsu.com>
> > Is my understanding above correct?
> 
> No.  I simply meant DropRelFileNodeBuffers() calls the following function,
> and avoids the optimization if it returns InvalidBlockNumber.
> 
> 
> BlockNumber
> smgrcachednblocks(SMgrRelation reln, ForkNumber forknum) {
>       return reln->smgr_cached_nblocks[forknum];
> }

Thank you for clarifying. 

So in the new function, it goes something like:
        if (InRecovery)
        {
                if (reln->smgr_cached_nblocks[forknum] != InvalidBlockNumber)
                        return reln->smgr_cached_nblocks[forknum];
                else
                        return InvalidBlockNumber;
        }

I've revised the patch and added the new function accordingly in the attached 
file.
I also did not remove the duplicate code from smgrnblocks because Amit-san 
mentioned
that when the caching for non-recovery cases is implemented, we can use it
for non-recovery cases as well.

Although I am not sure if the way it's written in DropRelFileNodeBuffers is 
okay.
BlockNumberIsValid(nTotalBlocks)
 
                        nTotalBlocks = smgrcachednblocks(smgr_reln, forkNum[j]);
                        nBlocksToInvalidate = nTotalBlocks - firstDelBlock[j];

                        if (BlockNumberIsValid(nTotalBlocks) &&
                                nBlocksToInvalidate < 
BUF_DROP_FULLSCAN_THRESHOLD)
                        {
                                //enter optimization loop
                        }
                        else
                        {
                                //full scan for each fork  
                        }

Regards,
Kirk Jamison

v17-Optimize-DropRelFileNodeBuffers-during-recovery.patch
Description: v17-Optimize-DropRelFileNodeBuffers-during-recovery.patch

v1-Prevent-invalidating-blocks-in-smgrextend-during-recovery.patch
Description: v1-Prevent-invalidating-blocks-in-smgrextend-during-recovery.patch