Hi all
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
select pg_column_size('{1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0}'::double
precision[]) return 104 --- I'am lost because I expected 10*16 + 16 = 176.
It is neither 16+10*8 (96)
So what is happening behind the scene, I did not found any documentation.
Since the queries are done in memory I suppose no compression is going on.
Furthermore select
pg_column_size('{1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0}'::double
precision[]) return 104 as well. So I discard compression.
The whole point is that in the application I work on, we store double arrays
as bytea (using some serialization before storing the data).
I was very surprised to see that the storage of an array of double take more
space using double precision[] than serializing it and storing it into a
bytea.
Thanks for any help and docs
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