| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>, pgsql-bugs(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: [HACKERS] Cursor with hold emits the same row more than once across commits in 8.3.7 |
| Date: | 2009-06-09 17:47:14 |
| Message-ID: | 23358.1244569634@sss.pgh.pa.us |
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| Lists: | pgsql-bugs pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> This seems like the only option that will produce correct answers, so
> it gets my vote. How much is the performance penalty for
> materializing the tuplestore? I'm inclined to think that whatever it
> is, you just have to pay it if you ask for a WITH HOLD cursor.
I don't mind paying it for a WITH HOLD cursor, since by definition
you're asking for a more expensive behavior there. The thing that is
bothering me more is whether we want to pay a price for a *non* WITH
HOLD cursor. You can get instability for seqscan or volatile functions
if you just try MOVE BACKWARD ALL and re-read.
regards, tom lane
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