RE: [Patch] Optimize dropping of relation buffers using dlist - Mailing list pgsql-hackers

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

>     From: Jamison, Kirk/ジャミソン カーク <k.jamison@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