Re: FW: performance issue with a 2.5gb joinded table

-----Original Message-----
From: Heikki Linnakangas [mailto:hlinnakangas(at)vmware(dot)com]
Sent: Donnerstag, 3. Januar 2013 18:02
To: Daniel Westermann
Cc: 'pgsql-performance(at)postgresql(dot)org'
Subject: Re: [PERFORM] FW: performance issue with a 2.5gb joinded table

On 03.01.2013 15:30, Daniel Westermann wrote:
> What additionally makes me wonder is, that the same table in oracle is taking much less space than in postgresql:
>
> SQL> select sum(bytes) from dba_extents where segment_name =
> SQL> 'TEST1';
> SUM(BYTES)
> ----------
> 1610612736
>
> select pg_relation_size('mgmtt_own.test1');
> pg_relation_size
> ------------------
> 2502082560
> (1 row)
>
> (sysdba(at)[local]:7777) [bi_dwht]> \d+ mgmtt_own.test1
> Table "mgmtt_own.test1"
> Column | Type | Modifiers | Storage | Description
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> ------------------------------+---------------+-----------+---------+-
> slsales_batch | numeric(8,0) | | main |
> slsales_checksum | numeric(8,0) | | main |
> slsales_reg_id | numeric(8,0) | | main |
> slsales_prod_id | numeric(8,0) | | main |
> slsales_date_id | numeric(8,0) | | main |
> slsales_pos_id | numeric(8,0) | | main |
> slsales_amt_sales_gross | numeric(16,6) | | main |
> slsales_amt_sales_discount | numeric(16,6) | | main |
> slsales_units_sales_gross | numeric(8,0) | | main |
> slsales_amt_returns | numeric(16,6) | | main |
> slsales_amt_returns_discount | numeric(16,6) | | main |
> slsales_units_returns | numeric(8,0) | | main |
> slsales_amt_est_winnings | numeric(16,6) | | main |
> Indexes:
> "itest1" btree (slsales_date_id) CLUSTER, tablespace "mgmtt_idx"
> "itest2" btree (slsales_prod_id), tablespace "mgmtt_idx"
> Has OIDs: no
> Tablespace: "mgmtt_dat"

One difference is that numerics are stored more tightly packed on Oracle. Which is particularly good for Oracle as they don't have other numeric data types than number. On PostgreSQL, you'll want to use int4 for ID-fields, where possible. An int4 always takes up 4 bytes, while a numeric holding an integer value in the same range is typically 5-9 bytes.

- Heikki

Thanks for poiting that out, Heikki.