This is an excellent idea – unfortunately I’m in Maui right now (Mahalo!) and I’m not getting to testing with this. My first try was with 8.0.3 and it’s an 8.1 function I presume.
Not to be lazy – but any hint as to how to do the same thing for 8.0?
- Luke
On 11/21/05 9:10 PM, "Mark Kirkwood" <markir@xxxxxxxxxxxxxxx> wrote:
Luke Lonergan wrote:
> So that leaves the question - why not more than 64% of the I/O scan rate?
> And why is it a flat 64% as the I/O subsystem increases in speed from
> 333-400MB/s?
>
It might be interesting to see what effect reducing the cpu consumption
entailed by the count aggregation has - by (say) writing a little bit
of code to heap scan the desired relation (sample attached).
Cheers
Mark
/*
* fastcount.c
*
* Do a count that uses considerably less CPU time than an aggregate.
*/
#include "postgres.h"
#include "funcapi.h"
#include "access/heapam.h"
#include "catalog/namespace.h"
#include "utils/builtins.h"
extern Datum fastcount(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(fastcount);
Datum
fastcount(PG_FUNCTION_ARGS)
{
text *relname = PG_GETARG_TEXT_P(0);
RangeVar *relrv;
Relation rel;
HeapScanDesc scan;
HeapTuple tuple;
int64 result = 0;
/* Use the name to get a suitable range variable and open the relation. */
relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
rel = heap_openrv(relrv, AccessShareLock);
/* Start a heap scan on the relation. */
scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
{
result++;
}
/* End the scan and close up the relation. */
heap_endscan(scan);
heap_close(rel, AccessShareLock);
PG_RETURN_INT64(result);
}
