Re: I'd like to discuss scaleout at PGCon

From: Ashutosh Bapat
> In order to normalize parse trees, we need to at
> least replace various OIDs in parse-tree with something that the
> foreign server will understand correctly like table name on the
> foreign table pointed to by local foreign table OR (schema
qualified)
> function names  and so on.

Yes, that's the drawback of each node in the cluster having different
OIDs for the same object.  That applies to XL, too.  In XL, the data
node returns the data type names of the columns in the result set to
the coordinator.  Then the coordinator seemed to parse each data type
name with base_yyparse() to convert the name to its OID on the
coordinator.  That's why base_yyparse() appeared at the top in the
perf profile.  That repeated typename-to-OID conversion would be
reduced by caching the conversion result, like the logical replication
of PostgreSQL does.  But managing the catalog at one place and using
the same OID values seems to concise to me as a concept.


Regards
MauMau


-----Original Message----- 
From: Ashutosh Bapat
Sent: Saturday, June 2, 2018 1:00 AM
To: Tom Lane
Cc: MauMau ; Robert Haas ; PostgreSQL Hackers
Subject: Re: I'd like to discuss scaleout at PGCon

On Fri, Jun 1, 2018 at 11:27 AM, Tom Lane  wrote:
> Ashutosh Bapat  writes:
>> In order to avoid double parsing, we might want to find a way to
pass
>> a "normalized" parse tree down to the foreign server. We need to
>> normalize the OIDs in the parse tree since those may be different
>> across the nodes.
>
> I don't think this is a good idea at all.  It breaks any hope of
> supporting remote servers that are not the identical version to the
local
> one (since their parsetrees might be different).  And "normalized
OIDs"
> sounds like "pie in the sky".  You might get away with asssuming
that
> built-in functions have stable OIDs, but you can't expect that for
> functions in extensions.

Sorry for confusing writeup. I didn't mean "normalized OIDs" as I
mentioned in my last sentence. I meant "normalized parse-tree" as in
the first sentence. In order to normalize parse trees, we need to at
least replace various OIDs in parse-tree with something that the
foreign server will understand correctly like table name on the
foreign table pointed to by local foreign table OR (schema qualified)
function names  and so on. There might be more things to "normalize"
in the parse tree other than OIDs, but I can't think of anything right
now.


-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company