Using array instead of sub table (storage and speed)

Hi,

I have two tables

s {

id bigint NOT NULL PRIMARY KEY,

...

}

sp {

id bigint PRIMARY KEY,

sid bigint REFERENCES s (id),

i numeric,

m numeric

...

}

I have for each entry in [s] on average around 120 entries in [sp]. And
that table has become the largest table in my database (8.81565*10^09
entries).

Data in [sp] are never changed. I can probably reduce the size by
changing datatypes from numeric to float but I was wondering if it would
be more efficient - primarily in terms of storage - to change the
structure to have two arrays in [s]. E.g.

s {

id bigint NOT NULL PRIMARY KEY,

i numeric[],

m numeric[],

...

}

I can probably reduce the size by changing datatypes from numeric to
float/double. so final table would look like this:

s {

id bigint NOT NULL PRIMARY KEY,

i float[],

m double[],

...

}

I haven't really found anything yet how much space (e.g. how many bytes)
an array will use compared to a table row in postgresql.

Thanks

Lutz

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