| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Boszormenyi Zoltan <zb(at)cybertec(dot)at> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Meskes <meskes(at)postgresql(dot)org>, Noah Misch <noah(at)leadboat(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, PG Hackers <pgsql-hackers(at)postgresql(dot)org>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Hans-Jürgen Schönig <hs(at)cybertec(dot)at> |
| Subject: | Re: Modify the DECLARE CURSOR command tag depending on the scrollable flag |
| Date: | 2013-11-27 20:47:13 |
| Message-ID: | 1996.1385585233@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Boszormenyi Zoltan <zb(at)cybertec(dot)at> writes:
> If you consider all these:
> - certain combinations of query and DECLARE stmt flags fail;
> - adding NO SCROLL is breaking backward compatibility;
> - the readahead code has to really know whether the cursor is
> scrollable so it can behave just like the server;
If you're claiming that readahead inside ECPG will behave absolutely
transparently in all cases, I think that's bogus anyway. Consider for
example a query that will get a divide-by-zero error when it computes
the 110th row --- but the application stops after fetching 100 rows.
Everything's fine, until you insert some readahead logic. Queries
containing volatile functions might also not be happy about readahead.
Given these considerations, I think it'd be better to allow explicit
application control over whether read-ahead happens for a particular
query. And I have no problem whatsoever with requiring that the cursor
be explicitly marked SCROLL or NO SCROLL before read-ahead will occur.
regards, tom lane
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