On Wed, Dec 23, 2020 at 1:07 PM k.jami...@fujitsu.com <k.jami...@fujitsu.com> wrote: > > On Tuesday, December 22, 2020 9:11 PM, Amit Kapila wrote: > > > In this code, I am slightly worried about the additional cost of each time > > checking smgrexists. Consider a case where there are many relations and only > > one or few of them have not cached the information, in such a case we will > > pay the cost of smgrexists for many relations without even going to the > > optimized path. Can we avoid that in some way or at least reduce its usage > > to > > only when it is required? One idea could be that we first check if the > > nblocks > > information is cached and if so then we don't need to call smgrnblocks, > > otherwise, check if it exists. For this, we need an API like > > smgrnblocks_cahced, something we discussed earlier but preferred the > > current API. Do you have any better ideas? > > Right. I understand the point that let's say there are 100 relations, and > the first 99 non-local relations happen to enter the optimization path, but > the last > one does not, calling smgrexist() would be too costly and waste of time in > that case. > The only solution I could think of as you mentioned is to reintroduce the new > API > which we discussed before: smgrnblocks_cached(). > It's possible that we call smgrexist() only if smgrnblocks_cached() returns > InvalidBlockNumber. > So if everyone agrees, we can add that API smgrnblocks_cached() which will > Include the "cached" flag parameter, and remove the additional flag > modifications > from smgrnblocks(). In this case, both DropRelFileNodeBuffers() and > DropRelFileNodesAllBuffers() will use the new API. >
Yeah, let's do it that way unless anyone has a better idea to suggest. -- With Regards, Amit Kapila.
