tuple statistics function

Here is a revised version of pg_stattuple, which shows how many tuples
are "dead" etc. Per Tom's suggestion, a statistic of free/resuable
space is now printed.

test=# select pgstattuple('accounts');
NOTICE: physical length: 39.06MB live tuples: 100000 (12.59MB, 32.23%) dead tuples: 200000 (25.18MB, 64.45%) free/reusable space: 0.04MB (0.10%) overhead: 3.22%
pgstattuple
-------------
64.453125

What I'm not sure is:

o Should I place any kind of lock after reading buffer?

o Should I use similar algorithm to the one used in vacuum to determin
whether the tuple is "dead" or not?

Suggestions?
--
Tatsuo Ishii

-------------------------------------------------------------------------
/*
* $Header: /home/t-ishii/repository/pgstattuple/pgstattuple.c,v 1.2 2001/08/30 06:21:48 t-ishii Exp $
*
* Copyright (c) 2001 Tatsuo Ishii
*
* Permission to use, copy, modify, and distribute this software and
* its documentation for any purpose, without fee, and without a
* written agreement is hereby granted, provided that the above
* copyright notice and this paragraph and the following two
* paragraphs appear in all copies.
*
* IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT,
* INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
* LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
* DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
* THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS
* IS" BASIS, AND THE AUTHOR HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
* SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
*/

#include "postgres.h"
#include "fmgr.h"
#include "access/heapam.h"
#include "access/transam.h"

PG_FUNCTION_INFO_V1(pgstattuple);

extern Datum pgstattuple(PG_FUNCTION_ARGS);

/* ----------
* pgstattuple:
* returns the percentage of dead tuples
*
* C FUNCTION definition
* pgstattuple(NAME) returns FLOAT8
* ----------
*/
Datum
pgstattuple(PG_FUNCTION_ARGS)
{
Name p = PG_GETARG_NAME(0);

Relation rel;
HeapScanDesc scan;
HeapTuple tuple;
BlockNumber nblocks;
BlockNumber block = InvalidBlockNumber;
double table_len;
uint64 tuple_len = 0;
uint64 dead_tuple_len = 0;
uint32 tuple_count = 0;
uint32 dead_tuple_count = 0;
double tuple_percent;
double dead_tuple_percent;

Buffer buffer = InvalidBuffer;
uint64 free_space = 0; /* free/reusable space in bytes */
double free_percent; /* free/reusable space in % */

rel = heap_openr(NameStr(*p), NoLock);
nblocks = RelationGetNumberOfBlocks(rel);
scan = heap_beginscan(rel, false, SnapshotAny, 0, NULL);

while ((tuple = heap_getnext(scan,0)))
{
if (HeapTupleSatisfiesNow(tuple->t_data))
{
tuple_len += tuple->t_len;
tuple_count++;
}
else
{
dead_tuple_len += tuple->t_len;
dead_tuple_count++;
}

if (!BlockNumberIsValid(block) ||
block != BlockIdGetBlockNumber(&tuple->t_self.ip_blkid))
{
block = BlockIdGetBlockNumber(&tuple->t_self.ip_blkid);
buffer = ReadBuffer(rel, block);
free_space += PageGetFreeSpace((Page)BufferGetPage(buffer));
ReleaseBuffer(buffer);
}
}
heap_endscan(scan);
heap_close(rel, NoLock);

table_len = (double)nblocks*BLCKSZ;

if (nblocks == 0)
{
tuple_percent = 0.0;
dead_tuple_percent = 0.0;
free_percent = 0.0;
}
else
{
tuple_percent = (double)tuple_len*100.0/table_len;
dead_tuple_percent = (double)dead_tuple_len*100.0/table_len;
free_percent = (double)free_space*100.0/table_len;
}

elog(NOTICE,"physical length: %.2fMB live tuples: %u (%.2fMB, %.2f%%) dead tuples: %u (%.2fMB, %.2f%%) free/reusable space: %.2fMB (%.2f%%) overhead: %.2f%%",

table_len/1024/1024, /* phsical length in MB */

tuple_count, /* number of live tuples */
(double)tuple_len/1024/1024, /* live tuples in MB */
tuple_percent, /* live tuples in % */

dead_tuple_count, /* number of dead tuples */
(double)dead_tuple_len/1024/1024, /* dead tuples in MB */
dead_tuple_percent, /* dead tuples in % */

(double)free_space/1024/1024, /* free/available space in MB */

free_percent, /* free/available space in % */

/* overhead in % */
(nblocks == 0)?0.0: 100.0
- tuple_percent
- dead_tuple_percent
- free_percent);

PG_RETURN_FLOAT8(dead_tuple_percent);
}