Re: Index on a Decrypt / Bytea2Text Function

In response to Anthony Presley <anthony(at)resolution(dot)com>:

> Hi all,
>
> We tend to do a lot of lookups on our database that look something like:
>
> select
> e.id
> from
> employee e ,app_user au
> where
> au.id=user_id and
> au.corporation_id=$1 and
> e.ssn is not null and
> e.ssn!=' ' and
> e.ssn!='' and
> e.deleted='N'and
> bytea2text(DECRYPT(decode(e.ssn,'hex'), text2bytea(cast(e.id as text)),
> 'bf'))=$2
>
> The analyze here looks like:
>
> > explain analyze select e.id from employee e ,app_user au where
> au.id=user_id and au.corporation_id=41197 and e.ssn is not null and
> e.ssn!=' ' and e.ssn!='' and e.deleted='N'and
> bytea2text(DECRYPT(decode(e.ssn,'hex'), text2bytea(cast(e.id as text)),
> 'bf'))='188622250';
>
> QUERY
> PLAN
> --------------------------------------------------------------------------
> Nested Loop (cost=0.00..19282.05 rows=122 width=8) (actual
> time=24.591..192.435 rows=1 loops=1)
> -> Index Scan using emp_del on employee e (cost=0.00..18625.99
> rows=122 width=16) (actual time=24.556..192.398 rows=1 loops=1)
> Index Cond: (deleted = 'N'::bpchar)
> Filter: ((ssn IS NOT NULL) AND (ssn <> ' '::text) AND (ssn <>
> ''::text) AND (bytea2text(decrypt(decode(ssn, 'hex'::text),
> text2bytea((id)::text), 'bf'::text)) = '188622250'::text))
> -> Index Scan using app_user_pkey on app_user au (cost=0.00..5.36
> rows=1 width=8) (actual time=0.032..0.033 rows=1 loops=1)
> Index Cond: (au.id = e.user_id)
> Filter: (au.corporation_id = 41197)
> Total runtime: 192.565 ms
> (8 rows)
>
> It would appear that almost 100% of this time is taken up by doing the
> bytea2text and decrypt() functions.
>
> How would I create an index based on the results of the decrypt and
> bytea2text function to improve this select statement?

The best way would be to unencrypt the column and use a normal index.

Since you're simply using a value in another column as the key anyway,
your design has created all the performance headaches of encryption
with no actual security.

--
Bill Moran
http://www.potentialtech.com
http://people.collaborativefusion.com/~wmoran/