On Fri, Apr 24, 2020 at 5:24 PM David Rowley <dgrowle...@gmail.com> wrote:
> On Fri, 24 Apr 2020 at 15:26, Andy Fan <zhihui.fan1...@gmail.com> wrote: > > > > Actually I have a different opinion to handle this issue, to execute the > > a > (select avg(a) from tinner where x = touer.x); The drawback of > current > > path is because it may calculates the same touer.x value multi-times. So > > if we cache the values we have calculated before, we can avoid the cost. > > Material path may be the one we can reference but it assumes all the > tuples > > in the tuplestore matches the input params, which is not the fact here. > > > > But what if the input params doesn't change? If so we can use Material > path > > to optimize this case. But since we don't know if the if the input > params changed > > or not during plan time, we just add the path (let's assume we can add > it with some > > rules or cost calculation). If the input params is not changed, we use > the cached > > values, if the input params changed, we can ReScan the Material node. > To optimize > > the the cache invalidation frequent issue like (1, 2, 1, 2, 1, 2) case, > we may consider > > a sort path to change the input values to (1, 1, 1, 2, 2, 2). But > overall it is a big effort. > > This does not seem quite right to me. What you need is some sort of > parameterized materialize. Materialize just reads its subnode and > stores the entire thing input and reuses it any time that it > rescanned. > > You likely need something more like what is mentioned in [1]. There's > also a bunch of code from Heikki in the initial email in that thread. > Heikki put it in nodeSubplan.c. I think it should be a node of its > own. > > Glad to see your feedback, David:). Actually I thought about this idea some time ago, but since we have to implement a new path and handle the cached data is too huge case, I gave it up later. When I am working on some other stuff, I found Material path with some chgParam change may get a no harmful improvement with less effort, based on we know how to add the material path and we can always get a correct result. I will check the link you provide when I get time, It's a nice feature and it will be a good place to continue working on that feature. Best Regards Andy Fan
