From: Joe Conway <mail@joeconway.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Hackers (PostgreSQL) <pgsql-hackers@postgresql.org>
Subject: Re: VALUES clause memory optimization
Date: Sat, 26 Aug 2006 13:08:03 -0700
Message-ID: <44F0AA23.9030800@joeconway.com> (raw)
In-Reply-To: <200608260335.k7Q3ZeJ04955@momjian.us>
References: <200608260335.k7Q3ZeJ04955@momjian.us>
Bruce Momjian wrote:
> Has this been addressed?
>
>>Tom Lane wrote:
>>>The reason we could safely list_free inside transformInsertRow is that
>>>we know all its callers have just built the passed-in list and so there
>>>are no other pointers to it. That doesn't apply in the general case of
>>>grammar output.
After another look, even in this case there could be other pointers.
Starting around line 667 of analyze.c:
8<------------------
foreach(lc, selectQuery->targetList)
{
TargetEntry *tle = (TargetEntry *) lfirst(lc);
Expr *expr;
if (tle->resjunk)
continue;
if (tle->expr &&
(IsA(tle->expr, Const) ||IsA(tle->expr, Param)) &&
exprType((Node *) tle->expr) == UNKNOWNOID)
expr = tle->expr;
else
expr = (Expr *) makeVar(rtr->rtindex,
tle->resno,
exprType((Node *) tle->expr),
exprTypmod((Node *) tle->expr),
0);
exprList = lappend(exprList, expr);
}
/* Prepare row for assignment to target table */
exprList = transformInsertRow(pstate, exprList,
stmt->cols,
icolumns, attrnos);
8<------------------
So in the UNKNOWNOID case, it wouldn't be safe to free the node after
transformation because it originates in the grammar output. The *only*
safe thing to free up would be a the input exprList itself. Not much to
be saved there.
>>>My advice is to get that low-hanging fruit
>>>in transformInsertRow and leave the other ideas for 8.3.
This one case doesn't provide that much memory savings by itself anyway.
I guess we'll just live with it until we can come up with a safe way to
free grammar output.
Joe
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Subject: Re: VALUES clause memory optimization
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