Re: Tupple statistics function

> Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp> writes:
> > I have written a small function that show how many tuples are dead
> > etc. in a specified table.
>
> Dead according to whose viewpoint? Under MVCC this seems to be
> in the eye of the beholder...
>
> > Shall I add this function into contrib directory?
>
> No real objection, but you should carefully document exactly what
> the results mean.
>
> BTW, I'd suggest accounting for free, reusable space separately from
> "overhead".
>
> regards, tom lane

Ok, here are the source code...

/*
* $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.
*/

#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;
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;

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++;
}
}
heap_endscan(scan);
heap_close(rel, NoLock);

table_len = (double)nblocks*BLCKSZ;

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

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

table_len/1024/1024,

tuple_count,
(double)tuple_len/1024/1024,
tuple_percent,

dead_tuple_count,
(double)dead_tuple_len/1024/1024,
dead_tuple_percent,

(nblocks == 0)?0.0: 100.0 - tuple_percent - dead_tuple_percent);

PG_RETURN_FLOAT8(dead_tuple_percent);
}