Re: Postgres delays function returning large set of data - Mailing list pgsql-hackers

Pavel Stehule wrote:
> 
> Hello
> 
> can you send source code? There are two types of C SRF functions. One
> returns row ro by row, second store returned rows and returns block.
> What did you use?
> 

I had originally used the style that returns row by row, but after reading
the page i created a new function which returns a block.  This version runs
slightly faster (12.5 seconds to run my test case) but it is still far
slower than expected.

A few notes on the code:
getdata function returns an array with length 2*size, the first size
elements are one colum the other size elements are the next column.
I have timed the call getdata and determined it consumes on average around
30ms of my test case's run time.

<code>
PG_FUNCTION_INFO_V1(getTableFastHDF5);

Datum
getTableFastHDF5(PG_FUNCTION_ARGS)
{ /*{{{*//* Locals */ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;FuncCallContext *fcc;TupleDesc
tupdesc;Tuplestorestate*tupstore;MemoryContext per_query_ctx;MemoryContext oldcontext;AttInMetadata *attinmeta;int
*data;intsize;int i;
 
if (!connections)    ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("No
connections open, use openHDF5 to open a file first")));
data = getdata(textToStr(PG_GETARG_TEXT_P(0)), PG_GETARG_INT32(1),
PG_GETARG_INT32(2), &size, TEMPORARY_CONTEXT);
per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;oldcontext = MemoryContextSwitchTo(per_query_ctx);
tupdesc = rsinfo->expectedDesc;tupstore = tuplestore_begin_heap(true, false, SortMem);

if (data == NULL)    ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("Could not
find specified data in file")));

for (i = 0; i < size; i++){   /*{{{*/    Datum val[2];    bool nulls[2];    HeapTuple tup;
    MemoryContextSwitchTo(oldcontext);

    MemSet(nulls, false, 2 * sizeof(bool));

    /* fill strings to be turned into tuple */    val[0] = Int32GetDatum(data[i]);    val[1] = Int32GetDatum(data[i +
size]);
    /* make tuple */    tup = heap_form_tuple(tupdesc, val, nulls);
    /* make tuple to datum so it can be returned */    MemoryContextSwitchTo(per_query_ctx);
tuplestore_puttuple(tupstore,tup);
 
    /* return, but there is more to send */   /*}}}*/}/* return and finish sending */
tuplestore_donestoring(tupstore);
MemoryContextSwitchTo(oldcontext);
rsinfo->returnMode = SFRM_Materialize;rsinfo->setResult = tupstore;rsinfo->setDesc = tupdesc;
return (Datum) 0;

/*}}}*/
}
</code>


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