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Re: Status of server side Large Object support?

From: Joe Conway <mail(at)joeconway(dot)com>
To: Thomas Hallgren <thhal(at)mailblocks(dot)com>
Cc: Peter Eisentraut <peter_e(at)gmx(dot)net>,"pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>,bryan(at)bulten(dot)ca
Subject: Re: Status of server side Large Object support?
Date: 2004-11-28 18:50:16
Message-ID: 41AA1DE8.9050202@joeconway.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Thomas Hallgren wrote:
> Peter Eisentraut wrote:
>> Am Sonntag, 28. November 2004 12:33 schrieb Thomas Hallgren:
>>
>>> Hmm, ok. But there's no way to stream them in and out from disk. From
>>> what I can see, you have to bring all of it into memory. Not so ideal
>>> perhaps if you want to provide streaming media for thousands of users.
>>
>> You can use the substring function to read the pieces you need.
>>
> Won't the substring function bring the whole thing into memory in the 
> backend before it pass you the piece you need? Let's assume I want to 
> stream 4k at a time of a 40mb image, that's a whole lot of byte swapping 
> if that's the case.

Not if the column is storage type EXTERNAL. See a past discussion here:
http://archives.postgresql.org/pgsql-general/2003-07/msg01447.php


> How do you handle writes without first creating the whole image in memory?

You can't currently, but it would be a nice addition ;-)

I agree with Peter -- I think effort is better spent improving bytea.

BTW, someone on GENERAL just started a very similar thread 
("implementing a lo_truncate operation, and possibly a lo_size"). I've 
cc'd him here.

Joe

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