Re: [HACKERS] Avoiding io penalty when updating large objects

Tom Lane wrote:
> Alvaro Herrera <alvherre(at)surnet(dot)cl> writes:
>
>>On Tue, Jun 28, 2005 at 07:38:43PM -0700, Mark Dilger wrote:
>>
>>>If, for a given row, the value of c is, say, approximately 2^30 bytes
>>>large, then I would expect it to be divided up into 8K chunks in an
>>>external table, and I should be able to fetch individual chunks of that
>>>object (by offset) rather than having to detoast the whole thing.
>
>
>>I don't think you can do this with the TOAST mechanism. The problem is
>>that there's no API which allows you to operate on only certain chunks
>>of data.
>
>
> There is the ability to fetch chunks of a toasted value (if it was
> stored out-of-line but not compressed). There is no ability at the
> moment to update it by chunks. If Mark needs the latter then large
> objects are probably the best bet.
>
> I'm not sure what it'd take to support chunkwise update of toasted
> fields. Jan, any thoughts?
>
> regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
> subscribe-nomail command to majordomo(at)postgresql(dot)org so that your
> message can get through to the mailing list cleanly

Ok,

If there appears to be a sane path to implementing this, I may be able to
contribute engineering effort to it. (I manage a group of engineers and could
spare perhaps half a man year towards this.) But I would like direction as to
how you all think this should be done, or whether it is just a bad idea.

I can also go with the large object approach. I'll look into that.

Mark Dilger