Re: proposal: lob conversion functionality

On 12.08.2013 21:08, Pavel Stehule wrote:
> 2013/8/10 Tom Lane<tgl@sss.pgh.pa.us>:
>> Pavel Stehule<pavel.stehule@gmail.com>  writes:
>>> I found so there are no simple API for working with LO from PL without
>>> access to file system.
>>
>> What?  See lo_open(), loread(), lowrite(), etc.
>
> yes, so there are three problems with these functions:
>
> a) probably (I didn't find) undocumented

It's there, although it's a bit difficult to find by searching. See:
http://www.postgresql.org/docs/devel/static/lo-funcs.html.

I don't actually agree with this phrase on that page:

> The ones that are actually useful to call via SQL commands are
> lo_creat, lo_create, lo_unlink, lo_import, and lo_export

Calling lo_open, loread and lowrite seems equally useful to me.

> b) design with lo handler is little bit PL/pgSQL unfriendly.

It's a bit awkward, I agree.

> c) probably there is a bug - it doesn't expect handling errors
>
> postgres=# select fbuilder.attachment_to_xml(0);
> WARNING:  Snapshot reference leak: Snapshot 0x978f6f0 still referenced
>   attachment_to_xml
> ───────────────────
>   [null]
> (1 row)

Yeah, that's a server-side bug. inv_open() registers the snapshot before
checking if the large object exists. If it doesn't, the
already-registered snapshot is not unregistered, hence the warning.

I've committed the attached fix for that bug.

- Heikki