You write:
Each customer can have multiple sites, but only one should be
displayed in this list.
Yet, your query retrieves all rows. That would be a point to optimize. But you also do not define which site is to be picked.
Either way, it does not matter much here. Your EXPLAIN shows only 5026 rows for the site scan (5018 for the customer scan). So hardly any customer actually has more than one site. Did you ANALYZE your tables before running EXPLAIN?
From the numbers I see in your EXPLAIN, indexes will give you nothing for this query. Sequential table scans will be the fastest possible way. Half a second is rather slow for 5000 rows, though. Maybe your database needs some general performance tuning?
Maybe the query itself is faster, but "half a second" includes network transfer? EXPLAIN ANALYZE would tell us more.
If this query is your bottleneck, I would suggest you implement a materialized view.
After you provided more information I find that my diagnosis pretty much holds.
The query itself needs 27 ms. Not much of a problem there. "Half a second" was the kind of misunderstanding I had suspected. The slow part is the network transfer (plus ssh encoding / decoding, possibly rendering). You should only retrieve 100 rows, that would solve most of it, even if it means to execute the whole query every time.
If you go the route with a materialized view like I proposed you could add a serial number without gaps to the table plus index on it - by adding a column row_number() OVER (<your sort citeria here>) AS mv_id.
Then you can query:
SELECT *
FROM materialized_view
WHERE mv_id >= 2700
AND mv_id < 2800;
This will perform very fast. LIMIT / OFFSET cannot compete, that needs to compute the whole table before it can sort and pick 100 rows.
pgAdmin timing
When you execute a query from the query tool, the message pane shows something like:
Total query runtime: 62 ms.
And the status line shows the same time. I quote pgAdmin help about that:
The status line will show how long the last query took to complete. If
a dataset was returned, not only the elapsed time for server execution
is displayed, but also the time to retrieve the data from the server
to the Data Output page.
If you want to see the time on the server you need to use SQL EXPLAIN ANALYZE or the built in Shift + F7keyboard shortcut or Query -> Explain analyze. Then, at the bottom of the explain output you get something like this:
Total runtime: 0.269 ms
It sounds like what you probably want is to:
Create a role to own all the common tables and schema, or just use your own if you really will always be the only one with full control of the main tables.
Create another role you intend to give only read-only access to the shared tables and schemas. GRANT that role rights using GRANT SELECT ON ALL TABLES IN SCHEMA [x] for each shared schema. You may also want to ALTER DEFAULT PRIVILEGES to make sure this role has read rights on any new tables created in these schemas too.
Now GRANT each user membership of the read-only access role with INHERIT.
For the private schemas, create a schema the same as the user's username with CREATE SCHEMA [username] AUTHORIZATION [username] or the older style where you create the schema then ALTER SCHEMA ... OWNER TO.
See the postgresql manual for the detailed syntax of all of the above commands. Start with user management, part of the broader database administration topic that includes grant management etc. The PostgreSQL manual is detailed, comprehensive and readable: reading it is strongly recommended.
Best Answer
Made a backup of the database, restrored it.
In the new database the invalid, nameless view has been dropped by pgadmin.