Re: type unknown - how important is it? - Mailing list pgsql-hackers

Shachar,

I think with type oid 705 (unknown) it's safe to treat it as text. 
Certainly better than punting.

On another note are you aware of any issues with transactions? 
Specifically with using the dated autocommit mode ?

Dave

Shachar Shemesh wrote:

> Tom Lane wrote:
>
>> Dave Cramer <pg@fastcrypt.com> writes:
>>  
>>
>>> I just had a customer complain about this. My understanding is that 
>>> unkown is a constant which has not been typed yet. Is it possible 
>>> for it to be a binary type, if so how ?
>>> I would think it should only ever be a string?
>>>   
>>
>>
>> You can read "unknown" as "string literal for which the query does not
>> provide sufficient context to assign a definite type".  I dunno what the
>> OLE driver really needs to do with the datatype info, but I suppose that
>> treating this as equivalent to "text" is not unreasonable.  Ask the
>> complainant what *he* thinks it should do.
>>
>>             regards, tom lane
>>  
>>
> If JDBC can postpone the understanding what the type is until it's 
> being requested, all I can say is "lucky them". OLE DB isn't so lucky. 
> We need to actually report what type each column of a query is.
>
> To make matters worse, there is almost not a single type that can 
> simply be passed along from PG to the caller. PG sends numbers in 
> network byte order, while OLE DB typically reports them in little 
> endian. We do our queries in UTF-8, while we need to return them in 
> UTF-16, and so on and so forth. Typically, just about any type you 
> would care to mention would need conversion of one type or another. I 
> shudder to remember what I had to do with dates.
>
> So OLE DB performs the query in binary mode. Anything else would not 
> make much sense anyways. The "unknown" error may be a result of PG not 
> recognizing the type, as Tom mentioned, but it may also be a result of 
> OLE DB not recognizing the type. If the later is the case, OLE DB of 
> sufficiently late versions should report what OID the missing type 
> has, if not through the usual OLE error mechanisms, then through a log 
> file you can set through the registry. Read the docs for more info.
>
> Most new types are actually fairly easy to add. With some types, 
> however, one would need to understand what is the expected behavior. 
> This is not as simple as one would expect, as most people use ADO 
> rather than OLE DB directly. Still, a question (to the oledb-dev list, 
> preferably) saying "PG type #696 should be returned as DBTYPE_UINT4" 
> would almost guarantee quick response, as it's fairly easy to handle 
> (in most cases). If this is not a PG built in type then things are a 
> little more complicated. Non-built in types have non-constant OIDs, 
> and are identified by name on session startup. This means that OLE DB 
> cannot handle a type that is only added to the database after the 
> session started (not normally a problem). Also, I cannot possibly 
> report non-standard types unless I know how to parse them. I'll 
> probably add code to handle all unknown types as BLOBs or something, 
> but I cannot give a time frame for that. I'm also not certain how 
> helpful that would be for most cases.
>
> On the good news front, Version 1.0.0.17 is about ready to be released 
> (initial schema support). I am resuming development after about half a 
> year of doing other stuff.
>
>             Shachar
>

-- 
Dave Cramer
http://www.postgresintl.com
519 939 0336
ICQ#14675561