Hi Pavel
Thanks you for your answer. here is a procedure that works :
- CREATE TABLE cartedecredit(card_id SERIAL PRIMARY KEY, username
VARCHAR(100), cc bytea);
- INSERT INTO cartedecredit(username,cc) SELECT 'individu ' || x.id,
pgp_sym_encrypt('test value ' || x.id, 'motdepasse','compress-algo=2,
cipher-algo=aes256') FROM generate_series(1,100000) AS x(id);
- CREATE INDEX idx_cartedecredit_cc02 ON
cartedecredit(pgp_sym_decrypt(cc, 'motdepasse','compress-algo=2,
cipher-algo=aes256'));
- SELECT pgp_sym_decrypt(cc, 'motdepasse') FROM cartedecredit WHERE
pgp_sym_decrypt(cc, 'motdepasse','compress-algo=2, cipher-algo=aes256')='test
value 32';
pgp_sym_decrypt
-----------------
test value 32
(1 row)
Time: 2.237 ms
- explain analyze SELECT pgp_sym_decrypt(cc, 'motdepasse') FROM
cartedecredit WHERE pgp_sym_decrypt(cc, 'motdepasse','compress-algo=2,
cipher-algo=aes256')='test value 32';
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
Index Scan using idx_cartedecredit_cc02 on cartedecredit (cost=0.42..8.44
rows=1 width=32) (actual time=1.545..1.546 rows=1 loops=1)
Index Cond: (pgp_sym_decrypt(cc, 'motdepasse'::text, 'compress-algo=2,
cipher-algo=aes256'::text) = 'test value 32'::text)
Planning time: 0.330 ms
Execution time: 1.580 ms
(4 rows)
OK that works great.
Thank you for the recommendation
Best Regards
[cid:image002.png@01D14E0E.8515EB90]
Didier ROS
Expertise SGBD
DS IT/IT DMA/Solutions Groupe EDF/Expertise Applicative - SGBD
Nanterre Picasso - E2 565D (aile nord-est)
32 Avenue Pablo Picasso
92000 Nanterre
didier....@edf.fr<mailto:didier....@edf.fr>
support-postgres-nive...@edf.fr<mailto:support-postgres-nive...@edf.fr>
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De : pavel.steh...@gmail.com [mailto:pavel.steh...@gmail.com]
Envoyé : samedi 6 octobre 2018 12:14
À : ROS Didier <didier....@edf.fr>
Cc : pgsql-...@lists.postgresql.org; pgsql-performa...@lists.postgresql.org;
pgsql-general@lists.postgresql.org
Objet : Re: Why the index is not used ?
so 6. 10. 2018 v 11:57 odesílatel ROS Didier
<didier....@edf.fr<mailto:didier....@edf.fr>> napsal:
Hi
I would like to submit the following problem to the PostgreSQL community. In my
company, we have data encryption needs.
So I decided to use the following procedure :
(1) Creating a table with a bytea type column to store the encrypted data
CREATE TABLE cartedecredit(card_id SERIAL PRIMARY KEY, username VARCHAR(100),
cc bytea);
(2) inserting encrypted data
INSERT INTO cartedecredit(username,cc) SELECT 'individu ' ||
x.id<http://x.id>, pgp_sym_encrypt('test value ' || x.id<http://x.id>,
'motdepasse','compress-algo=2, cipher-algo=aes256') FROM
generate_series(1,100000) AS x(id);
(3) Querying the table
SELECT pgp_sym_decrypt(cc, 'motdepasse') FROM cartedecredit WHERE
pgp_sym_decrypt(cc, 'motdepasse')='test value 32';
pgp_sym_decrypt
-----------------
test value 32
(1 row)
Time: 115735.035 ms (01:55.735)
-> the execution time is very long. So, I decide to create an index
(4) Creating an index on encrypted data
CREATE INDEX idx_cartedecredit_cc02 ON cartedecredit(cc);
this index cannot to help.
but functional index can cartedecredit(pgp_sym_decrypt(cc, 'motdepasse').
Unfortunately index file will be decrypted in this case.
CREATE INDEX ON
(5) Querying the table again
SELECT pgp_sym_decrypt(cc, 'motdepasse') FROM cartedecredit WHERE
pgp_sym_decrypt(cc, 'motdepasse')='test value 32';
pgp_sym_decrypt
-----------------
test value 32
(1 row)
Time: 118558.485 ms (01:58.558) -> almost 2 minutes !!
postgres=# explain analyze SELECT pgp_sym_decrypt(cc, 'motdepasse') FROM
cartedecredit WHERE pgp_sym_decrypt(cc, 'motdepasse')='test value 32';
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------
Seq Scan on cartedecredit (cost=0.00..3647.25 rows=500 width=32) (actual
time=60711.787..102920.509 rows=1 loops=1)
Filter: (pgp_sym_decrypt(cc, 'motdepasse'::text) = 'test value 32'::text)
Rows Removed by Filter: 99999
Planning time: 0.112 ms
Execution time: 102920.585 ms
(5 rows)
==> the index is not used in the execution plan. maybe because of the use of a
function in the WHERE clause. I decide to modify the SQL query
(6) Querying the table
SELECT pgp_sym_decrypt(cc, 'motdepasse') FROM cartedecredit WHERE
cc=pgp_sym_encrypt('test value 32', 'motdepasse');
it is strange - this should to use index, when there is usual index over cc
column.
What is result of explain analyze when you penalize seq scan by
set enable_seqscan to off
pgp_sym_decrypt
-----------------
(0 rows)
Time: 52659.571 ms (00:52.660)
==> The execution time is very long and I get no result (!?)
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------
Seq Scan on cartedecredit (cost=0.00..3646.00 rows=1 width=32) (actual
time=61219.989..61219.989 rows=0 loops=1)
Filter: (cc = pgp_sym_encrypt('test value 32'::text, 'motdepasse'::text))
Rows Removed by Filter: 100000
Planning time: 0.157 ms
Execution time: 61220.035 ms
(5 rows)
==> My index is not used.
QUESTIONS :
- why I get no result ?
- why the index is not used?
Thanks in advance
Best Regards
Didier
[cid:image002.png@01D14E0E.8515EB90]
Didier ROS
Expertise SGBD
DS IT/IT DMA/Solutions Groupe EDF/Expertise Applicative - SGBD
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