Обсуждение: Determine dead tuples size

Hello guys,

is it possible to determine dead tuples size for table?

--
Alexey Romanchuk

Try the contrib module pgstattuple.

2007/3/15, Alexey Romanchuk <aromanchuk@swsoft.com>:
> Hello guys,
>
> is it possible to determine dead tuples size for table?
>
> --
> Alexey Romanchuk
>
>
>
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--
Daniel Cristian Cruz
Analista de Sistemas

On Thu, Mar 15, 2007 at 01:58:47PM +0600, Alexey Romanchuk wrote:
> is it possible to determine dead tuples size for table?

See contrib/pgstattuple.

--
Michael Fuhr

Hello, Michael.

> On Thu, Mar 15, 2007 at 01:58:47PM +0600, Alexey Romanchuk wrote:
>> is it possible to determine dead tuples size for table?

> See contrib/pgstattuple.

thanks, i install contribs and try to analyze result of pgstattuple
function and found it strange.

Here it is output:
                             pgstattuple
----------------------------------------------------------------------
 (233242624,1186804,206555428,88.56,20707,3380295,1.45,13896816,5.96)

When i try to sum all size (live, dead and free) the sum is not equal
total size. For this table 206555428 + 3380295 + 13896816 = 223832539.
The difference between total and sum is 9410085. It is near 5%.

Is it ok?

--
Alexey Romanchuk

Alexey Romanchuk wrote:
> thanks, i install contribs and try to analyze result of pgstattuple
> function and found it strange.

Try "SELECT * FROM pgstattuple('foo')", that'll tell you what the
columns are. Take a look at README.pgstattuple as well for more details.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

Alexey Romanchuk <aromanchuk@swsoft.com> writes:
> When i try to sum all size (live, dead and free) the sum is not equal
> total size. For this table 206555428 + 3380295 + 13896816 = 223832539.
> The difference between total and sum is 9410085. It is near 5%.

pgstattuple is a bit simplistic: it doesn't count the page headers or
item pointers at all.  It looks to me like it also fails to consider
the effects of alignment padding --- if a tuple's length is shown as
63, that's what it counts, even though the effective length is 64.
(This might not be a problem in practice --- I'm not sure if the stored
t_len has always been maxaligned or not.)

            regards, tom lane