Обсуждение: does timestamp precision affect storage size?

i'm cleaning up some queries for performance, and noticed that we never use precision beyond the second (ie,
`timestamp(0)`)in our business logic. 

would there be any savings in storage or performance improvements from losing the resolution on fractional seconds, or
are`timestamp(precision)` effectively the same for storage as `timestamp`?  (based on docs, I assume the latter but
wantedto check) 

On 21/06/16 22:39, Jonathan Vanasco wrote:
> i'm cleaning up some queries for performance, and noticed that we never use precision beyond the second (ie,
`timestamp(0)`)in our business logic. 
>
> would there be any savings in storage or performance improvements from losing the resolution on fractional seconds,
orare `timestamp(precision)` effectively the same for storage as `timestamp`?  (based on docs, I assume the latter but
wantedto check) 

No, there are no space savings here.

=# select pg_column_size('now'::timestamptz(0)),
pg_column_size('now'::timestamptz);

 pg_column_size | pg_column_size
----------------+----------------
              8 |              8
(1 row)

--
Vik Fearing                                          +33 6 46 75 15 36
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support

Jonathan Vanasco <postgres@2xlp.com> writes:
> would there be any savings in storage or performance improvements from losing the resolution on fractional seconds,

Storage-wise, no.  If you have a resolution spec on your columns now,
I think dropping the resolution spec would save you a few nanoseconds per
row insertion due to not having to apply the roundoff function.  Adding
one would certainly not improve speed.

            regards, tom lane

On Jun 21, 2016, at 4:50 PM, Tom Lane wrote:

> Storage-wise, no.  If you have a resolution spec on your columns now,
> I think dropping the resolution spec would save you a few nanoseconds per
> row insertion due to not having to apply the roundoff function.  Adding
> one would certainly not improve speed.


On Jun 21, 2016, at 4:47 PM, Vik Fearing wrote:
> No, there are no space savings here.
>
> =# select pg_column_size('now'::timestamptz(0)),
> pg_column_size('now'::timestamptz);


Thanks.  I thought that was happening, but wanted to make sure.  the allure of shaving a byte or two off some rows
couldn'tbe ignored ;)