The indexes that can be useful and should be considered deal with
WHERE c.root = 100
AND cs.catalog = c.id
AND cs.securitygroup = 200
AND cu.catalog = c.id
AND cu.university = 300
So the following fields can be interesting for indexes
c: id, root
cs: catalog, securitygroup
cu: catalog, university
So, try creating
(catalog_securitygroup.catalog, catalog_securitygroup.securitygroup)
and
(catalog_university.catalog, catalog_university.university)
EDIT:
I missed the ORDER BY - these fields should also be considered, so
(catalog.name, catalog.id)
might be beneficial (or some other composite index that could be used for sorting and the conditions - possibly (catalog.root, catalog.name, catalog.id))
EDIT2
Although another question is accepted I'll provide some more food for thought.
I have created some test data and run some benchmarks.
The test cases are minimal in terms of record width (in catalog_securitygroup and catalog_university the primary keys are (catalog, securitygroup) and (catalog, university)). Here is the number of records per table:
test=# SELECT (SELECT COUNT(*) FROM catalog), (SELECT COUNT(*) FROM catalog_securitygroup), (SELECT COUNT(*) FROM catalog_university);
?column? | ?column? | ?column?
----------+----------+----------
500000 | 1497501 | 500000
(1 row)
Database is postgres 8.4, default ubuntu install, hardware i5, 4GRAM
First I rewrote the query to
SELECT c.id, c.name, c.owner
FROM catalog c, catalog_securitygroup cs, catalog_university cu
WHERE c.root < 50
AND cs.catalog = c.id
AND cu.catalog = c.id
AND cs.securitygroup < 200
AND cu.university < 200
ORDER BY c.name
LIMIT 50 OFFSET 100
note: the conditions are turned into less then to maintain comparable number of intermediate rows (the above query would return 198,801 rows without the LIMIT clause)
If run as above, without any extra indexes (save for PKs and foreign keys) it runs in 556 ms on a cold database (this is actually indication that I oversimplified the sample data somehow - I would be happier if I had 2-4s here without resorting to less then operators)
This bring me to my point - any straight query that only joins and filters (certain number of tables) and returns only a certain number of the records should run under 1s on any decent database without need to use cursors or to denormalize data (one of these days I'll have to write a post on that).
Furthermore, if a query is returning only 50 rows and does simple equality joins and restrictive equality conditions it should run even much faster.
Now let's see if I add some indexes, the biggest potential in queries like this is usually the sort order, so let me try that:
CREATE INDEX test1 ON catalog (name, id);
This makes execution time on the query - 22ms on a cold database.
And that's the point - if you are trying to get only a page of data, you should only get a page of data and execution times of queries such as this on normalized data with proper indexes should take less then 100ms on decent hardware.
I hope I didn't oversimplify the case to the point of no comparison (as I stated before some simplification is present as I don't know the cardinality of relationships between catalog and the many-to-many tables).
So, the conclusion is
- if I were you I would not stop tweaking indexes (and the SQL) until I get the performance of the query to go below 200ms as rule of the thumb.
- only if I would find an objective explanation why it can't go below such value I would resort to denormalisation and/or cursors, etc...
Best Answer
I discovered the answer! It was tricky.
In "apache2.conf", I originally had
ServerName 74.181.105.228
, which makes accessing 74.181.105.228 via a browser load the default page for my server.Changing this value in "apache2.conf" to
ServerName mydomain.com
solves the problem since Apache no longer directs 74.181.105.228 to the default page of my server. In turn, I can direct 74.181.105.228 to load a page from a certain directory in my file system.My virtual host block still remains