[HACKERS] Writing values to relation using bytearray ...
Hi,
I am trying to write values of different types to relation using following
code.
if(typbyval)
{
min_ba = (bytea *) palloc(len+1+VARHDRSZ);
memcpy(VARDATA(min_ba), min_datum, len);
SET_VARSIZE(min_ba, len+VARHDRSZ);
VARDATA(min_ba)[len] = '\0';
values[Anum_pg_partition_minval-1]= (Datum)min_ba ;
max_ba = (bytea *) palloc(len+1+VARHDRSZ);
memcpy(VARDATA(max_ba), max_datum, len);
SET_VARSIZE(max_ba, len+VARHDRSZ);
VARDATA(max_ba)[len] = '\0';
values[Anum_pg_partition_maxval-1]=(Datum)max_ba;
}
else
{
values[Anum_pg_partition_minval-1]=min_datum;
values[Anum_pg_partition_maxval-1]=max_datum;
}
These values are then written to relation using heap_form_tuple() and
simple_heap_insert() functions.
I am using following code to read the values from relation.
part_attr = heap_getattr (pg_parttup,Anum_pg_partition_maxval,
pg_partrel-rd_att,isnull);
if ( typbyval )
{
short_datum = 0;
memcpy(short_datum, VARDATA_ANY(part_attr), len);
part_attr = short_datum;
}
else if (len != -1 )
part_attr = (Datum)VARDATA_ANY(part_attr);
The aforementioned code works fine for types like int, data, text and I can
read values from the relation correctly. The problem arises for type
float8 which is not by value type and it has fixed length (8) where I
can't read the values written to relation correctly.
Am i missing something here?
Thanking you in anticipation.
With warm regards,
--
Kedar.
Re: [HACKERS] Writing values to relation using bytearray ...
On Fri, Mar 6, 2009 at 10:03 AM, Kedar Potdar kedar.pot...@gmail.com wrote: The aforementioned code works fine for types like int, data, text and I can read values from the relation correctly. The problem arises for type float8 which is not by value type and it has fixed length (8) where I can't read the values written to relation correctly. Am i missing something here? Well as you've correctly diagnosed, not all byvalue data types are variable-length. This code all seems unnecessary. The whole point of heap_form_datum and heap_deform_datum/heap_getattr is that you don't have to worry about all this. there are also functions like datumCopy() but you probably don't even need them here, you can just put the datums you have handy into the values[] array and pass that to heap_form_tuple -- it'll copy them into the resulting tuple so once you've formed the tuple you don't have to worry about the lifetime of the original datums. heap_deform_tuple() and heap_getattr can return pointers into the original tuple so you do have to be careful to copy them if you need them to survive the original tuple -- but you might not be anyways. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Writing values to relation using bytearray ...
Thanks Greg, for showing interest. The problem here is I need to store values of different types into bytearray column of relation. On Fri, Mar 6, 2009 at 4:33 PM, Greg Stark st...@enterprisedb.com wrote: On Fri, Mar 6, 2009 at 10:03 AM, Kedar Potdar kedar.pot...@gmail.com wrote: The aforementioned code works fine for types like int, data, text and I can read values from the relation correctly. The problem arises for type float8 which is not by value type and it has fixed length (8) where I can't read the values written to relation correctly. Am i missing something here? Well as you've correctly diagnosed, not all byvalue data types are variable-length. This code all seems unnecessary. The whole point of heap_form_datum and heap_deform_datum/heap_getattr is that you don't have to worry about all this. there are also functions like datumCopy() but you probably don't even need them here, you can just put the datums you have handy into the values[] array and pass that to heap_form_tuple -- it'll copy them into the resulting tuple so once you've formed the tuple you don't have to worry about the lifetime of the original datums. heap_deform_tuple() and heap_getattr can return pointers into the original tuple so you do have to be careful to copy them if you need them to survive the original tuple -- but you might not be anyways. -- greg
Re: [HACKERS] Writing values to relation using bytearray ...
On Fri, Mar 6, 2009 at 11:41 AM, Kedar Potdar kedar.pot...@gmail.com wrote: Thanks Greg, for showing interest. The problem here is I need to store values of different types into bytearray column of relation. Oh, hm. I think you need to look at typlen instead of typbyval. But you have an additional problem for typbyval types: the pointer to Datum isn't necessarily pointing at the right bytes. I think you have to use the GET_[1248]_BYTES macros depending on typlen. There may be a helper function for this but I don't know of one. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Writing values to relation using bytearray ...
On Fri, Mar 6, 2009 at 12:01 PM, Greg Stark st...@enterprisedb.com wrote: But you have an additional problem for typbyval types: the pointer to Datum isn't necessarily pointing at the right bytes. I think you have to use the GET_[1248]_BYTES macros depending on typlen. There may be a helper function for this but I don't know of one. Actually on further thought I think I would suggest just storing the whole datum for all typbyval types setting your bytea length to SIZEOF_DATUM. And use datumGetSize() for non-typbyval datums. Assuming you have typbyval and typlen handy. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Writing values to relation using bytearray ...
Kedar Potdar kedar.pot...@gmail.com writes: The problem here is I need to store values of different types into bytearray column of relation. Perhaps you should study the ANALYZE code. AFAICS your requirements are not different from those of the pg_statistic data store. You should do things the same way they are done there, if only to reduce the surprise factor for readers of the code. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Writing values to relation using bytearray ...
Thanks Tom for your interest. I could find a workaround for the issue wherein the value of type which is not stored by value and has fixed data length, is being stored in string format to the relation. While retrieving from relation, this value is converted by using coerce_to_specific_type() to its native type datum represation as required. This is a bit of overhead and I'd like to find more efficient solution and will look pg_statistics data store. Regards, - Kedar - sent from a mobile device. On 3/6/09, Tom Lane t...@sss.pgh.pa.us wrote: Kedar Potdar kedar.pot...@gmail.com writes: The problem here is I need to store values of different types into bytearray column of relation. Perhaps you should study the ANALYZE code. AFAICS your requirements are not different from those of the pg_statistic data store. You should do things the same way they are done there, if only to reduce the surprise factor for readers of the code. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Writing values to relation using bytearray ...
Kedar Potdar kedar.pot...@gmail.com writes: I could find a workaround for the issue wherein the value of type which is not stored by value and has fixed data length, is being stored in string format to the relation. The answer is simple: don't do that. You do not need to, and should not, convert to string format. Again, please look at how ANALYZE does it. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
