From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Jim Nasby <jim(at)nasby(dot)net>, Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: estimating # of distinct values |
Date: | 2011-01-18 17:32:11 |
Message-ID: | 27305.1295371931@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Jan 18, 2011 at 12:23 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
>> On Jan 17, 2011, at 8:11 PM, Robert Haas wrote:
> On Mon, Jan 17, 2011 at 7:56 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
>>> - Forks are very possibly a more efficient way to deal with TOAST than having separate tables. There's a fair amount of overhead we pay for the current setup.
>
> That seems like an interesting idea, but I actually don't see why it
> would be any more efficient, and it seems like you'd end up
> reinventing things like vacuum and free space map management.
>>
>> The FSM would take some effort, but I don't think vacuum would be that hard to deal with; you'd just have to free up the space in any referenced toast forks at the same time that you vacuumed the heap.
> How's that different from what vacuum does on a TOAST table now?
Even more to the point: Jim hasn't provided one single reason to suppose
that this would be better-performing than the existing approach. It
looks to me like a large amount of work, and loss of on-disk
compatibility, for nothing at all except the sake of change.
regards, tom lane
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