Hi, On 2017-01-25 05:45:24 +0100, Pavel Stehule wrote: > 2017-01-25 1:35 GMT+01:00 Andres Freund <and...@anarazel.de>: > > > On 2017-01-24 21:32:56 -0300, Alvaro Herrera wrote: > > > Andres Freund wrote: > > > > Hi, > > > > > > > > On 2017-01-24 17:38:49 -0300, Alvaro Herrera wrote: > > > > > +static Datum ExecEvalTableExpr(TableExprState *tstate, ExprContext > > *econtext, > > > > > + bool *isnull); > > > > > +static Datum ExecEvalTableExprFast(TableExprState *exprstate, > > ExprContext *econtext, > > > > > + bool *isNull); > > > > > +static Datum tabexprFetchRow(TableExprState *tstate, ExprContext > > *econtext, > > > > > + bool *isNull); > > > > > +static void tabexprInitialize(TableExprState *tstate, ExprContext > > *econtext, > > > > > + Datum doc); > > > > > +static void ShutdownTableExpr(Datum arg); > > > > > > > > To me this (and a lot of the other code) hints quite strongly that > > > > expression evalution is the wrong approach to implementing this. What > > > > you're essentially doing is building a vulcano style scan node. Even > > if > > > > we can this, we shouldn't double down on the bad decision to have these > > > > magic expressions that return multiple rows. There's historical reason > > > > for tSRFs, but we shouldn't add more weirdness like this. > > > > > > Thanks for giving it a look. I have long thought that this patch would > > > be at odds with your overall executor work. > > > > Not fundamentally, but it makes it harder. > > > > If you plan to hold support SRFin target list, then nothing is different. > In last patch is executed under nodeProjectSet.
It is, because we suddenly need to call different functions - and I'm revamping most of execQual to have an opcode dispatch based execution model (which then also can be JITed). > > > XMLTABLE is specified by the standard to return multiple rows ... but > > > then as far as my reading goes, it is only supposed to be supported in > > > the range table (FROM clause) not in the target list. I wonder if > > > this would end up better if we only tried to support it in RT. I asked > > > Pavel to implement it like that a few weeks ago, but ... > > > > Right - it makes sense in the FROM list - but then it should be an > > executor node, instead of some expression thingy. > > > > The XMLTABLE function is from user perspective, from implementation > perspective a form of SRF function. I use own executor node, because fcinfo > is complex already and not too enough to hold all information about result > columns. > The implementation as RT doesn't reduce code - it is just moving to > different file. You're introducing a wholly separate callback system (TableExprRoutine) for the new functionality. And that stuff is excruciatingly close to stuff that the normal executor already knows how to do. > I'll try to explain my motivation. Please, check it and correct me if I am > wrong. I don't keep on my implementation - just try to implement XMLTABLE > be consistent with another behave and be used all time without any > surprise. > > 1. Any function that produces a content can be used in target list. We > support SRF in target list and in FROM part. Why XMLTABLE should be a > exception? targetlist SRFs were a big mistake. They cause a fair number of problems code-wise. They permeated for a long while into bits of both planner and executor, where they really shouldn't belong. Even after the recent changes there's a fair amount of uglyness associated with them. We can't remove tSRFs for backward compatibility reasons, but that's not true for XMLTABLE Greetings, Andres Freund -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
