Re: proposal: lob conversion functionality
От | Pavel Stehule |
---|---|
Тема | Re: proposal: lob conversion functionality |
Дата | |
Msg-id | CAFj8pRCv5-rN2jj8X51QYiNgq6Y0ekkmr_845+W86E3NEg0Xuw@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: proposal: lob conversion functionality (Noah Misch <noah@leadboat.com>) |
Список | pgsql-hackers |
2013/10/21 Noah Misch <noah@leadboat.com>
On Mon, Sep 30, 2013 at 01:06:15PM +0300, Heikki Linnakangas wrote:All the other large object functions are named like lo*, so I think new ones
> 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.
should also be lo* rather than *_lo. One of the key benefits of large
objects, compared to a bytea column in some table, is their efficiency when
reading or writing only a subset of the object. However, the proposed
functions only deal with the large object as a whole. We could easily fix
that. Consider this list of new functions in their place:
lo_create(oid, bytea) RETURNS oid -- new LO with content (similar to make_lo)
lo_get(oid) RETURNS bytea -- read entire LO (same as load_lo)
lo_get(oid, bigint, int) RETURNS bytea -- read from offset for length
lo_put(oid, bigint, bytea) RETURNS void -- write data at offset
Anything we do here effectively provides wrappers around the existing
functions tailored toward the needs of libpq. A key outstanding question is
whether doing so provides a compelling increment in usability. On the plus
side, adding such functions resolves the weirdness of having a variety of
database object that is easy to access from libpq but awkward to access from
plain SQL. On the minus side, this could easily live as an extension module.
I have not used the large object facility to any significant degree, but I
generally feel this is helpful enough to justify core inclusion. Any other
opinions on the general suitability or on the specifics of the API offered?
fast reply - I reply again later in my office.
I don't think so new functions (for bytea type) has any sense in libpq. From C is usually better to use a native C interface than ensure conversion to bytea. Probably the interface libpq should be modernized, but it complete and enough now. I don't have a motivation to enhance a API now. And a fact, so proposed bytea functions are not in libpq is a reason why I used different naming convention. A main motivation was a access from PL to LO without obscure patterns - mainly for PL/pgSQL. For other languages it is available - but maybe better direction is direct mapping to related primitives based on host environment possibilities.
Today evening I'll look on your proposal with some more time.
Regards
Pavel
Thanks,
nm
--
Noah Misch
EnterpriseDB http://www.enterprisedb.com
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