how can I speed up my queries? - mysql

Question

so I have a 560mb db with the largest table 500mb(over 10 million rows)
my query hase to join 5 tables and takes about 10 seconds to finish....
SELECT DISTINCT trips.tripid AS tripid,
stops.stopdescrption AS "perron",
Date_format(segments.segmentstart, "%H:%i") AS "time",
Date_format(trips.tripend, "%H:%i") AS "arrival",
Upper(routes.routepublicidentifier) AS "lijn",
plcend.placedescrption AS "destination"
FROM calendar
JOIN trips
ON calendar.vsid = trips.vsid
JOIN routes
ON routes.routeid = trips.routeid
JOIN places plcstart
ON plcstart.placeid = trips.placeidstart
JOIN places plcend
ON plcend.placeid = trips.placeidend
JOIN segments
ON segments.tripid = trips.tripid
JOIN stops
ON segments.stopid = stops.stopid
WHERE stops.stopid IN ( 43914, 23899, 23925, 23908,
23913, 19899, 23871, 43902,
23876, 25563, 18956, 19912,
23889, 23861, 23879, 23884,
23856, 19920, 19898, 23916,
23894, 20985, 23930, 20932,
20986, 22434, 20021, 19893,
19903, 19707, 19935 )
AND calendar.vscdate = Str_to_date('25-10-2011', "%e-%c-%Y")
AND segments.segmentstart >= Str_to_date('15:56', "%H:%i")
AND routes.routeservicetype = 0
AND segments.segmentstart > "00:00:00"
ORDER BY segments.segmentstart
what are things I can do to speed this up? any tips are welcome, i'm pretty new to sql...
but I can't change the structure of the db because it's not mine...

Answer 1

Use EXPLAIN to find the bottlenecks: http://dev.mysql.com/doc/refman/5.0/en/explain.html
Then perhaps, add indexes.
If you don't need to select ALL rows, use LIMIT to limit returned result count.

Answer 2

Just looking at the query, I would say that you should make sure that you have indexes on trips.vsid, calendar.vscdate, segments.segmentstart and routes.routeservicetype. I assume that there is already indexes on all the primary keys in the tables.
Using explain as Briedis suggested would show you how well the indexes work.
You might want to add covering indexes for some tables, like for example an index on trips.vsid where tripid and routeid are included. That way the database can use only the index for the data that is needed from the table, and not read from the actual table.
Edit:
The execution plan tells you that it successfully uses indexes for everything except the segments table, where it does a table scan and filters by the where condition. You should try to make a covering index for segments.segmentstart by including tripid and stopid.

Answer 3

Try adding a clusters index to the routes table on both routeservicetype and routeid.
Depending on the frequency of the data within the routeservicetype field, you may get an improvement by shrinking the amount of data being compared in the join to the trips table.
Looking at the explain plan, you may also want to force the sequence of the table usage by using STRAIGHT_JOIN instead of JOIN (or INNER JOIN), as I've had real improvements with this technique.
Essentially, put the table with the smallest row-count of extracted data at the beginning of the query, and the largest row count table at the end (in this case possibly the segments table?), with the exception of simple lookups (eg. for descriptions).
You may also consider altering the WHERE clause to filter the segments table on stopid instead of the stops table, and creating a clustered index on the segments table on (stopid, tripid and segmentstart) - this index will be effectively able to satisfy two joins and two where clauses from a single index...
To build the index...
ALTER TABLE segments ADD INDEX idx_qry_helper ( stopid, tripid, segmentstart );
And the altered WHERE clause...
WHERE segments.stopid IN ( 43914, 23899, 23925, 23908,
23913, 19899, 23871, 43902,
23876, 25563, 18956, 19912,
23889, 23861, 23879, 23884,
23856, 19920, 19898, 23916,
23894, 20985, 23930, 20932,
20986, 22434, 20021, 19893,
19903, 19707, 19935 )
:
:
At the end of the day, a 10 second response for what appears to be a complex query on a fairly large dataset, isn't all that bad!