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Re: xlog location arithmetic

From: Euler Taveira de Oliveira <euler(at)timbira(dot)com>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: xlog location arithmetic
Date: 2011-12-20 13:08:50
Message-ID: 4EF088E2.3090607@timbira.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 20-12-2011 07:27, Magnus Hagander wrote:
> On Tue, Dec 6, 2011 at 19:06, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Tue, Dec 6, 2011 at 1:00 PM, Euler Taveira de Oliveira
>> <euler(at)timbira(dot)com> wrote:
>>> On 06-12-2011 13:11, Robert Haas wrote:
>>>> On Tue, Dec 6, 2011 at 5:14 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
>>>>> I've been considering similar things, as you can find in the archives,
>>>>> but what I was thinking of was converting the number to just a plain
>>>>> bigint, then letting the user apply whatever arithmetic wanted at the
>>>>> SQL level. I never got around to acutally coding it, though. It could
>>>>> easily be extracted from your patch of course - and I think that's a
>>>>> more flexible approach. Is there some advantage to your method that
>>>>> I'm missing?
>>>>
>>>> I went so far as to put together an lsn data type.  I didn't actually
>>>> get all that far with it, which is why I haven't posted it sooner, but
>>>> here's what I came up with.  It's missing indexing support and stuff,
>>>> but that could be added if people like the approach.  It solves this
>>>> problem by implementing -(lsn,lsn) => numeric (not int8, that can
>>>> overflow since it is not unsigned), which allows an lsn => numeric
>>>> conversion by just subtracting '0/0'::lsn.
>>>>
>>> Interesting approach. I don't want to go that far. If so, you want to change
>>> all of those functions that deal with LSNs and add some implicit conversion
>>> between text and lsn data types (for backward compatibility). As of int8, I'm
> 
> As long as you have the conversion, you don't really need to change
> them, do you? It might be nice in some ways, but this is still a
> pretty internal operation, so I don't see it as critical.
> 
For correctness, yes.

At this point, my question is: do we want to support the lsn data type idea or
a basic function that implements the difference between LSNs?


-- 
   Euler Taveira de Oliveira - Timbira       http://www.timbira.com.br/
   PostgreSQL: Consultoria, Desenvolvimento, Suporte 24x7 e Treinamento

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