Re: double precision[] storage space questions

greg <gregory.jevardat@unige.ch> writes:
> I cannot find any documentation on the space taken by a double precision
> array. And the few tests I did surprise me.

> Here are a few tries I did to understand
> select pg_column_size(1.1::double precision)              return 8    --- as
> expected
> select pg_column_size('{}'::double precision[])           return 16  --- ok
> maybe an array header
> select pg_column_size('{1.111}'::double precision[])   return 32  --- I
> expected 16+ sizeof(double) = 24

'{}' is a zero-dimensional array so it doesn't have the same
dimensionality information that your third case does.  See
the comments at the head of
http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/include/utils/array.h;hb=HEAD

> The whole point is that in the application I work on, we store double arrays
> as bytea (using some serialization before storing the data).

TBH, that seems like a pretty silly decision.  It guarantees that you
cannot do any useful manipulations of the array on the database side.

            regards, tom lane