From: Luke Lonergan <llonergan@greenplum.com>
To: Mark Kirkwood <markir@paradise.net.nz>
Cc: pgsql-performance@postgresql.org, "eng@intranet.greenplum.com" <eng@intranet.greenplum.com>
Subject: Re: Hardware/OS recommendations for large databases (
Date: Wed, 23 Nov 2005 18:29:49 -0800
Message-ID: <BFAA659D.145E5%llonergan@greenplum.com> (raw)
In-Reply-To: <4382A840.3030401@paradise.net.nz>
Mark,
This is an excellent idea unfortunately I¹m in Maui right now (Mahalo!)
and I¹m not getting to testing with this. My first try was with 8.0.3 and
it¹s 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@paradise.net.nz> 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);
> }
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To: pgsql-performance@postgresql.org
Cc: llonergan@greenplum.com, markir@paradise.net.nz, eng@intranet.greenplum.com
Subject: Re: Hardware/OS recommendations for large databases (
In-Reply-To: <BFAA659D.145E5%llonergan@greenplum.com>
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