From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Mark Dilger <hornschnorter@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Missing dependency tracking for TableFunc nodes
Date: Tue, 12 Nov 2019 15:32:14 -0500
Message-ID: <27162.1573590734@sss.pgh.pa.us> (raw)
In-Reply-To: <20191112194720.ffzotjwcx6hgcnyy@alap3.anarazel.de>
References: <18427.1573508501@sss.pgh.pa.us>
<352b500b-9bf5-6e6a-fcf4-d9847738e977@gmail.com>
<42282535-a0a2-f2cf-c769-262f870bec9b@gmail.com>
<1690.1573571970@sss.pgh.pa.us>
<20191112194720.ffzotjwcx6hgcnyy@alap3.anarazel.de>
Andres Freund <andres@anarazel.de> writes:
> On 2019-11-12 10:19:30 -0500, Tom Lane wrote:
>> I could imagine annotations that say "this field contains a function OID"
>> or "this list contains collation OIDs" and then the find_expr_references
>> logic could be derived from that.
> I want to attach some annotations to types, rather than fields. I
> e.g. introduced a Location typedef, annotated as being ignored for
> equality purposes, instead of annotating each 'int location'. Wonder if
> we should also do something like that for your hypothetical "function
> OID" etc. above - seems like it also might give the human reader of code
> a hint.
Hm. We could certainly do "typedef FunctionOid Oid;",
"typedef CollationOidList List;" etc, but I think it'd get pretty
tedious pretty quickly --- just for this one purpose, you'd need
a couple of typedefs for every system catalog that contains
query-referenceable OIDs. Maybe that's better than comment-style
annotations, but I'm not convinced.
> Wonder if there's any way to write an assertion check that verifies we
> have the necessary dependencies. But the only idea I have - basically
> record all the syscache lookups while parse analysing an expression, and
> then check that all the necessary dependencies exist - seems too
> complicated to be worthwhile.
Yeah, it's problematic. One issue there that I'm not sure how to
resolve with autogenerated code, much less automated checking, is that
quite a few cases in find_expr_references know that we don't need to
record a dependency on an OID stored in the node because there's an
indirect dependency on something else. For example, in FuncExpr we
needn't log funcresulttype because the funcid is enough dependency,
and we needn't log either funccollid or inputcollid because those are
derived from the input expressions or the function result type.
(And giving up those optimizations would be pretty costly, 4x more
dependency checks in this example alone.)
For sure I don't want both "CollationOid" and "RedundantCollationOid"
typedefs, so it seems like annotation is the solution for this, but
I see no reasonable way to automatically verify such annotations.
Still, just writing down the annotations would be a way to expose
such assumptions for manual checking, which we don't really have now.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, andres@anarazel.de, hornschnorter@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: Missing dependency tracking for TableFunc nodes
In-Reply-To: <27162.1573590734@sss.pgh.pa.us>
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