Re: Why could different data in a table be processed with different performance?

On 28/09/18 11:56, Vladimir Ryabtsev wrote:
>
> > It could affect space storage, for the smaller blocks.
> But at which extent? As I understand it is not something about "alignment" to block size for rows? Is it only low-level IO thing with datafiles?
>

Maybe 'for the smaller blocks' was not very meaningful.
What i mean is 'in terms of wasted disk space: '

In an example:

create table test_space (i int);

empty table:

select pg_total_relation_size('test_space');
 pg_total_relation_size
------------------------
                      0
(1 row)

insert one single record:

insert into test_space values (1);

select pg_total_relation_size('test_space');
 pg_total_relation_size
------------------------
                   8192

select pg_relation_filepath('test_space');
 pg_relation_filepath
----------------------
 base/16384/179329

ls -alh base/16384/179329
-rw------- 1 postgres postgres 8.0K Sep 28 16:09 base/16384/179329

That means, if your block size was bigger, then you would have bigger space allocated for one single record.

regards,

fabio aprdi