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 + F7
keyboard shortcut or Query -> Explain analyze
. Then, at the bottom of the explain output you get something like this:
Total runtime: 0.269 ms
I have dealt with this issue before.
When you ran
select count(1) UserTableColumnCount from information_schema.columns
where table_schema='mysql' and table_name='user';
you should have gotten 42. That's how many columns MySQL 5.5 has for mysql.user
. Since you got 39, that means you must have upgraded from MySQL 5.1. That has 39 columns.
I wrote an earlier post about the number of columns in mysql.user
in different versions : MySQL service stops after trying to grant privileges to a user
Here is the post where I dealt with this : mysql: Restore All privileges to admin user
Hopefully you could run
# mysql_upgrade --upgrade-system-tables
to realign mysql.user
and have it autofill missing permissions with Y
.
Give it a Try !!!
If you want to try to fix the mysql.user manually, here are the steps:
#
# Backup the mysql.user table
#
CREATE TABLE mysql.user_backup LIKE mysql.user;
INSERT INTO mysql.user_backup SELECT * FROM mysql.user;
#
# Add Missing Columns
#
ALTER TABLE mysql.user
ADD COLUMN Create_tablespace_priv enum('N','Y') NOT NULL DEFAULT 'N'
AFTER Trigger_Priv
;
ALTER TABLE mysql.user ADD COLUMN plugin char(64);
ALTER TABLE mysql.user ADD COLUMN authentication_string text DEFAULT NULL;
#
# Give root user all privileges
#
UPDATE mysql.user SET
Select_priv='Y',Insert_priv='Y',Update_priv='Y',Delete_priv='Y',
Create_priv='Y',Drop_priv='Y',Reload_priv='Y',Shutdown_priv='Y',
Process_priv='Y',File_priv='Y',Grant_priv='Y',References_priv='Y',
Index_priv='Y',Alter_priv='Y',Show_db_priv='Y',Super_priv='Y',
Create_tmp_table_priv='Y',Lock_tables_priv='Y',Execute_priv='Y',
Repl_slave_priv='Y',Repl_client_priv='Y',Create_view_priv='Y',
Show_view_priv='Y',Create_routine_priv='Y',Alter_routine_priv='Y',
Create_user_priv='Y',Event_priv='Y',Trigger_priv='Y',
Create_tablespace_priv='Y'
WHERE user='root';
FLUSH PRIVILEGES;
That's it !!!
Best Answer
Assuming that "user" does not include any roles with superuser privileges (who can do everything), run this as owner of the table or superuser:
Users also need the
USAGE
privilege for theSEQUENCE
attached to theserial
column:About
serial
:.. and the
USAGE
privilege on the schema andCONNECT
of the database, both of which are the case for schemapublic
by default.If you only want a subset of users to be affected, grant privileges to a group role instead of
public
and grant membership in that role to those users. You still need to revoke privileges from the pseudo-rolepublic
, which can be viewed as the default group role granting membership to all (irrevocably). And grant whatever is still needed to others (by way of another group role, for instance).Related: